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Unit 2 – Unit 2 – Physics for your FuturePhysics for your Future

(EdExcel)

19/04/2319/04/23Topic 1 – Static and Current ElectricityTopic 1 – Static and Current Electricity

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The structure of the atomThe structure of the atom

ELECTRON – negative,

mass nearly nothing

PROTON – positive,

same mass as neutron

(“1”)

NEUTRON – neutral,

same mass as proton

(“1”)

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The structure of the atomThe structure of the atom

Particle Relative Mass Relative Charge

Proton 1 +1

Neutron 1 0

Electron 0 -1

MASS NUMBER = number of protons + number of neutrons

SYMBOL

PROTON NUMBER = number of protons (obviously)

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Static ElectricityStatic ElectricityStatic electricity is when charge “builds up” on an object and then stays “static”. How the charge builds up depends on what materials are used and the insulator can be charged up by friction by “transferring electrons”:

+ -

+-

+

+-

-

-+

+

+

-

-

+

+

+-

-

-

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Static ElectricityStatic Electricity

++

+ --

-

--

---

-

Short Static ExperimentsShort Static Experiments19/04/23

Try the following quick static electricity experiments:

1) Rubbing a balloon on your jumper and “sticking” it to the wall

2) Charging a plastic rod by rubbing it with a cloth and then holding it near the water from a smooth-running tap

3) Charging a plastic rod and trying to pick up small pieces of paper (or someone else’s hair!) with it

4) Rubbing a balloon on someone else’s head – you might want to ask their permission first…

Can you explain what you saw in each of these experiments?

Static Electricity in LightningStatic Electricity in Lightning19/04/23

e-e-

e-

e-

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Van de Graaf generatorsVan de Graaf generators

When a charge is neutralised by the movement of electrons either from the Earth or to the Earth we call this “earthing”

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Using Static in Paint SprayersUsing Static in Paint Sprayers

Connected to negative voltage

Connected to positive voltage

1) Why is the paint sprayer given a negative charge?

2) Why is the car given a positive charge?

19/04/23Dangers of Static – fuelling Dangers of Static – fuelling lineslines

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Electric CurrentElectric CurrentElectric current is a flow of negatively charged particles (i.e. electrons).

Note that electrons go from negative to positive-+ e-

e-

By definition, current is “the rate of flow of

charge”

Notice that the electrons from this battery only went in one direction around the circuit – this is called “direct current” (d.c.).

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Charge (Q)Charge (Q)

As we said, electricity is when electrons move around a circuit and carry energy with them. Each electron has a negative CHARGE. Charge is measured in Coulombs (C). We can work out how much charge flows in a circuit using the equation:

Q

TI

Charge = current x time

(in C) (in A) (in s)

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Example questionsExample questions

Charge (C) Current (A) Time (s)

5 2

0.4 1

20 0.5

50 250

3 60

1) A circuit is switched on for 30s with a current of 3A. How much charge flowed?

2) During electrolysis 6A was passed through some copper chloride and a charge of 1200C flowed. How long was the experiment on for?

3) A bed lamp is switched on for 10 minutes. It works on a current of 0.5A. How much charge flowed?

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Example questionsExample questions

Charge (C) Current (A) Time (s)

10 5 2

0.4 1 0.4

20 0.5 40

50 0.2 250

180 3 60

1) A circuit is switched on for 30s with a current of 3A. How much charge flowed?

2) During electrolysis 6A was passed through some copper chloride and a charge of 1200C flowed. How long was the experiment on for?

3) A bed lamp is switched on for 10 minutes. It works on a current of 0.5A. How much charge flowed?

90C

200s

300C

19/04/2319/04/23Topic 2 – Controlling and Using Electric CurrentTopic 2 – Controlling and Using Electric Current

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Circuit SymbolsCircuit Symbols

VA

Battery

Cell

Fuse

Resistor

LDR

Voltmeter

Ammeter

Variable resistor

Diode

Switch

Bulb

Thermistor

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Basic ideas…Basic ideas…Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____.

Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta.

Resistance is anything that resists an electric current. It is measured in _____.

Words: volts, amps, ohms, voltage, ammeter, voltmeter

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More basic ideas…More basic ideas…If a battery is added the current will ________ because there is a greater _____ on the electrons caused by a greater potential difference

If a bulb is added the current will _______ because there is greater ________ in the circuit

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Current in a series circuitCurrent in a series circuit

If the current here is 2 amps…

The current here will be…

The current here will be…

And the current here will be…

In other words, the current in a series circuit is THE SAME at any

point

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Current in a parallel circuitCurrent in a parallel circuitA PARALLEL circuit is one where the current has a “choice of routes”. Notice how current is “conserved” at each junction:

Here comes the current…

And the rest will go down here…

Half of the current will go down here (assuming the bulbs are the same)…

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Current in a parallel circuitCurrent in a parallel circuit

If the current here is 6 amps

The current here will be…

The current here will be…

The current here will be…

And the current here will be…

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Some example questions…Some example questions…

3A

6A

1A each

4A

2A

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Voltage in a series circuitVoltage in a series circuit

V

V V

If the voltage across the battery is 6V…

…and these bulbs are all identical…

…what will the voltage across each bulb be? 2V

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Voltage in a series circuitVoltage in a series circuit

V

V

If the voltage across the battery is 6V…

…what will the voltage across two bulbs be?

4V

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Voltage in a parallel circuitVoltage in a parallel circuit

If the voltage across the batteries is 4V…

What is the voltage here?

And here?

V

V4V

4V

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SummarySummary

In a SERIES circuit:

Current is THE SAME at any point

Voltage SPLITS UP over each component

In a PARALLEL circuit:

Current SPLITS UP down each “strand”

Voltage is THE SAME across each”strand”

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An example question:An example question:

V1

V2

6V

3A

A2

A3

V3

A1

3A

2A

1A

6V

3V 3V

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Another example question:Another example question:

V1

V2

10V3A

A2

A3

V3

A1

3A

1.2A

1.8A

6.7V

5V 5V

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Energy and chargeEnergy and charge

The amount of energy that flows in a circuit will depend on the amount of charge carried by the electrons and the voltage pushing the charge around:

W

QV

Energy transferred = charge x voltage

(in J) (in C) (in V)

By definition then, voltage means “energy transferred per

unit charge” and 1V = 1J/C

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Example questionsExample questions1) In a radio circuit a voltage of 6V is applied and

a charge of 100C flows. How much energy has been transferred?

2) In the above circuit the radio drew a current of 0.5A. How long was it on for?

3) A motor operates at 6V and draws a current of 3A. The motor is used for 5 minutes. Calculate: a) the charge flowing through it, b) the energy supplied to it

4) A lamp is attached to a 12V circuit and a charge of 1200C flows through it. If the lamp is on for 10 minutes calculate a) the current, b) the energy supplied to the bulb.

600J

200s

2A, 14,400J

900C, 5400J

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Georg Simon Ohm 1789-1854

ResistanceResistance

Resistance is anything that will RESIST a current. It is

measured in Ohms, a unit named after me.

The resistance of a component can be calculated using Ohm’s Law:

Resistance = Voltage (in V)

(in ) Current (in A)

V

RI

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An example question:An example question:

V

A

1) What is the resistance across this bulb?

2) Assuming all the bulbs are the same what is the total resistance in this circuit?

Voltmeter reads 10V

Ammeter reads 2A

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More examples…More examples…

12V

3A

3A

6V

4V

2A

1A

2V

What is the resistance of these bulbs?

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ResistanceResistanceResistance is anything that opposes an electric current.Resistance (Ohms, ) = Potential Difference (volts, V)

Current (amps, A)What is the resistance of the following:

1) A bulb with a voltage of 3V and a current of 1A.

2) A resistor with a voltage of 12V and a current of 3A

3) A diode with a voltage of 240V and a current of 40A

4) A thermistor with a current of 0.5A and a voltage of 10V

20

3

4

6

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Varying ResistanceVarying ResistanceRecall our earlier idea that if you increase the number of bulbs in a circuit you increase the resistance and therefore decrease the current:The same effect is seen when using a variable resistor:

Increase the

resistance:

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Resistors, bulbs and diodesResistors, bulbs and diodes

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Current-Voltage GraphsCurrent-Voltage Graphs

Voltage on powerpack/V

Current/A Voltage/V

1210…0…-10-12

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Current-voltage graphsCurrent-voltage graphsI

V

I

V

I

V

1. Resistor 3. Diode2. Bulb

Current increases in proportion to _______, provided the temperature doesn’t change

As voltage increases the bulb gets ______ and _______ increases due to increased vibrations in the ions in the filament

A diode only lets current go in one _______ – it has very _____ resistance in the other direction

Words – resistance, high, voltage, hotter, direction

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LDRs and ThermistorsLDRs and Thermistors

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Two simple components:Two simple components:

2) Thermistor – resistance DECREASES when temperature INCREASES

1) Light dependant resistor – resistance DECREASES when light intensity INCREASES

Resistance

Amount of light

Resistance

Temperature

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Understanding ResistanceWhen a voltage is applied it basically causes electrons to move towards the positive end of the battery:

Notice that the ions were vibrating and getting in the way of the electrons – this is resistance. This effect causes the metal to heat up.

IonsElectronsNegative Positive

Using this heating effectUsing this heating effect19/04/23

This heating effect can have its advantages and its disadvantages. For example, consider an old-fashioned light bulb:

This heating effect causes the filament to emit light…

…but it also causes a lot of energy to be wasted to the environment

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Electrical Power revisionElectrical Power revision

The amount of power being transferred in an electrical device is given by: P

IVPower = voltage x

current

in W in V in A1) How much power is transferred by a 230V fire that

runs on a current of 10A?

2) An electric motor has a power rating of 24W. If it runs on a 12V battery what current does it draw?

3) An average light bulb in a home has a power rating of 60W and works on 230V. What current does it draw?

Power is defined as “the rate of transferring energy” and is measured in units called “Watts” (W).

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Energy and PowerEnergy and PowerThe POWER RATING of an appliance is simply how much

energy it uses every second.

In other words, 1 Watt = 1 Joule per second

Energy transferred (J) = power (W) x time (s)

OR

Energy (J) = current (A) x voltage (V) x time (s)

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Some example questionsSome example questions1) A battery gives out a current of 0.2A and

has a voltage of 1.5V. If it is used for 30 seconds how much energy has it transferred?

2) An electric fire runs at a voltage of 230V and a current of 8A. If it is left on for 2 hours how much electrical energy has it transferred?

3) A toaster transfers 20,000J of electrical energy. If it runs at a voltage of 230V and a current of 2A how long was it on for?

4) A light bulb is left on overnight for 8 hours. If it transfers 1,000,000J of energy and runs on a voltage of 230V what current did it draw?

9J

13.2MJ

43.5s

0.15A

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Topic 3 – Motion and ForcesTopic 3 – Motion and Forces

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Some subtle differences…Some subtle differences…“Distance” is how far you have gone, “displacement” is how far you are from a point and can be positive or negative:

Start

1 metre-1 metre

Distance =

Displacement =

Distance =

Displacement =

Distance =

Displacement =

Distance =

Displacement =

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Some subtle differences…Some subtle differences…“Speed” means “how fast you are going”, “velocity” means “how far you are going in a certain direction”. If the following journeys take 1 second then work out:

Start

1 metre-1 metre

Speed =

Velocity =

Speed =

Velocity =

Speed =

Velocity =

Speed =

Velocity =

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Speed vs. VelocitySpeed vs. Velocity

1) Is this car travelling at constant speed?

2) Is this car travelling at constant velocity?

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Vector vs. scalarVector vs. scalarScalar quantities have size (“magnitude”) only and no

direction.

Vector quantities have both size and direction.

Scalar or vector???

Scalar Vector

1. Mass2. Distance

3. Displacement4. Speed

5. Velocity

6. Energy7. Time

8. Current9. Force

10. Acceleration

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Distance, Speed Distance, Speed and Timeand Time

Speed = distance (in metres)

time (in seconds)

D

TS

1) Freddie walks 200 metres in 40 seconds. What is his speed?

2) Hayley covers 2km in 1,000 seconds. What is her speed?

3) How long would it take Lauren to run 100 metres if she runs at 10m/s?

4) Jake travels at 50m/s for 20s. How far does he go?

5) Izzy drives her car at 85mph (about 40m/s). How long does it take her to drive 20km?

5m/s

2m/s

10s

1000m

500s

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Distance, Speed Distance, Speed and Timeand Time

Speed = distance (in metres)

time (in seconds)

D

TS

1) Sarah walks 2000m in 50 minutes. What is her speed in m/s?

2) Jack tries to walk the same distance at a speed of 5m/s. How long does he take?

3) James drives at 60mph (about 100km/h) for 3 hours. How far has he gone?

4) The speed of sound in air is 330m/s. Molly shouts at a mountain and hears the echo 3 seconds later. How far away is the mountain? (Careful!)

0.67m/s

400s

300km

495m

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Distance-time graphsDistance-time graphs

40

30

20

10

0 20 40 60 80 100

4) Diagonal line

downwards =

3) Steeper diagonal line =1) Diagonal line =

2) Horizontal line =

Distance

(metres)

Time/s

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40

30

20

10

0 20 40 60 80 100

1) What is the speed during the first 20 seconds?

2) How far is the object from the start after 60 seconds?

3) What is the speed during the last 40 seconds?

4) When was the object travelling the fastest?

Distance

(metres)

Time/s

0.5m/s

40m

1m/s

40-60s

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AccelerationAcceleration V-U

TA

Acceleration = change in velocity (in m/s)

(in m/s2) time taken (in s)1) A cyclist accelerates from 0 to 10m/s in 5 seconds.

What is her acceleration?

2) A ball is dropped and accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by?

3) A car accelerates from 10 to 20m/s with an acceleration of 2m/s2. How long did this take?

4) A rocket accelerates from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?

2m/s2

120m/s

5s

2000m/s2

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AccelerationAcceleration V-U

TA

Acceleration = change in velocity (in m/s)

(in m/s2) time taken (in s)1) Will accelerates from standstill to 50m/s in 25 seconds.

What is his acceleration?

2) Pierre accelerates at 5m/s2 for 5 seconds. He started at 10m/s. What is his new speed?

3) Elliott is in trouble with the police. He is driving up the A29 and sees a police car and brakes from 50m/s to a standstill. His deceleration was 10m/s2. How long did he brake for?

4) Another boy racer brakes at the same deceleration but only for 3 seconds. What speed did he slow down to?

2m/s2

35m/s

5s

20m/s

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Velocity-time graphsVelocity-time graphs

80

60

40

20

0 10 20 30 40 50

Velocity

m/s

T/s

1) Upwards line =

2) Horizontal line =

3) Upwards line =

4) Downward line =

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80

60

40

20

0

1) How fast was the object going after 10 seconds?

2) What is the acceleration from 20 to 30 seconds?

3) What was the deceleration from 30 to 50s?

4) How far did the object travel altogether?

10 20 30 40 50

Velocity

m/s

T/s

40m/s

2m/s2

3m/s2

1700m

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80

60

40

20

0

1) How fast was the object going after 10 seconds?

2) What is the acceleration from 20 to 30 seconds?

3) What was the deceleration from 40 to 50s?

4) How far did the object travel altogether?

10 20 30 40 50

Velocity

m/s

T/s

10m/s

4m/s2

6m/s2

1500m

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80

60

40

20

010 20 30 40 50

Velocity

m/s

T/s

This velocity-time graph shows Coryn’s journey to school. How far away does she live?

2500m

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Introduction to ForcesIntroduction to ForcesA force is a “push” or a “pull”. Some common examples:

Weight (mg) – pulls things towards the centre of the Earth

Air resistance/drag – a contact force that acts against

anything moving through air or liquid

Upthrust – keeps things afloat

Friction – a contact force that acts against anything

moving

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Free body force diagramsFree body force diagrams

The Earth pulls Newton down with a gravitational force of 700N.

Newton pulls the Earth up with a gravitational force of 700N.

what on what

direction

type

size

Action and reaction are equal and opposite!!

19/04/2319/04/23Balanced and unbalanced Balanced and unbalanced forcesforces

Consider a camel standing on a road. What forces are acting on it?

Weight

Reaction

These two forces would be equal – we say that they are BALANCED. The camel doesn’t move anywhere.

19/04/2319/04/23Balanced and unbalanced Balanced and unbalanced forcesforces

What would happen if we took the road away?

Weight

Reaction

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Air ResistanceAir ResistanceAir resistance is a force that opposes motion through air. The quicker you travel, the bigger the air resistance:

The same applies to a body falling through a liquid (called “drag” or “upthrust”).

19/04/2319/04/23Balanced and unbalanced Balanced and unbalanced forcesforces

19/04/2319/04/23Balanced and unbalanced Balanced and unbalanced forcesforces

1) This animal is either ________ or moving with _______ _____…

4) This animal is also either _______ or moving with ________ ______..

2) This animal is getting ________…

3) This animal is getting _______….

Words - Stationary, faster, slower or constant speed?

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SummarySummaryIf an object is stationary and has NO resultant force on it the object will…

If an object is stationary and a resultant force acts on it the object will…

If an object is already moving and NO resultant force acts on it the object will…

If an object is already moving and a resultant force acts on it the object will…

Complete these sentences…

…continue to stay stationary …accelerate in the direction of the resultant force

…continue to move at the same speed and the same direction

…accelerate in the direction of the resultant force

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Resultant ForceResultant ForceCalculate the resultant force of the following:

500N 100N 700N 600N

700N 700N

200N

800N 800N

100N

50N

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Force and accelerationForce and acceleration

If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:

Force (in N) = Mass (in kg) x Acceleration (in m/s2)

F

AM

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Force, mass and accelerationForce, mass and acceleration

1) A force of 1000N is applied to push a mass of 500kg. How quickly does it accelerate?

2) A force of 3000N acts on a car to make it accelerate by 1.5m/s2. How heavy is the car?

3) A car accelerates at a rate of 5m/s2. If it weighs 500kg how much driving force is the engine applying?

4) A force of 10N is applied by a boy while lifting a 20kg mass. How much does it accelerate by?

F

AM

2m/s2

2000kg

2500N

0.5m/s2

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Weight vs. MassWeight vs. MassEarth’s Gravitational Field Strength is 10N/kg. In other

words, a 1kg mass is pulled downwards by a force of 10N.

W

gM

Weight = Mass x Gravitational Field Strength

(in N) (in kg) (in N/kg)

1) What is the weight on Earth of a book with mass 2kg?

2) What is the weight on Earth of an apple with mass 100g?

3) James weighs 700N on the Earth. What is his mass?

4) On the moon the gravitational field strength is 1.6N/kg. What will James weigh if he stands on the moon?

20N

1N

70kg

112N

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Terminal VelocityTerminal VelocityConsider a skydiver:

1) At the start of his jump the air resistance is _______ so he _______ downwards.

2) As his speed increases his air resistance will _______

3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY

Words – increase, small, constant, balance,

accelerates

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Terminal VelocityTerminal Velocity

Consider a skydiver:

4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____.

5) Because he is slowing down his air resistance will _______ again until it balances his _________. The skydiver has now reached a new, lower ________ _______.

Words – slowing down, decrease, increases, terminal

velocity, weight

19/04/2319/04/23Velocity-time graph for terminal Velocity-time graph for terminal velocity…velocity…

Velocity

Time

Speed increases…

Terminal velocity reached…

Parachute opens – diver slows down

New, lower terminal velocity reached

Diver hits the ground

On the Moon

19/04/2319/04/23Topic 4 – Momentum, Energy, Work and PowerTopic 4 – Momentum, Energy, Work and Power

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Stopping a car…Stopping a car…

What two things must the driver of the car do in order to stop in time?

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Stopping a car…Stopping a car…

Braking distance

Too much alcoholThinking

distance

(reaction time)

Tiredness

Too many drugs

Wet/icy roads

Driving too fast

Tyres/brakes worn out

Heavy vehicle

Poor visibility

Total Stopping Distance = Thinking Distance + Braking Distance

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MomentumMomentumAny object that has both mass and velocity has MOMENTUM. Momentum (symbol “p”) is simply given by the formula:

Momentum = Mass x Velocity (in kgm/s) (in kg) (in m/s)

P

VM

What is the momentum of the following?

1) A 1kg football travelling at 10m/s

2) A 1000kg Ford Capri travelling at 30m/s

3) A 20g pen being thrown across the room at 5m/s

4) A 70kg bungi-jumper falling at 40m/s

10kgm/s

30,000kgm/s

0.1kgm/s

2800kgm/s

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Conservation of MomentumConservation of MomentumIn any collision or explosion momentum is conserved (provided that there are no external forces have an effect). Example question:

Two cars are racing around the M25. Car A collides with the back of car B and the cars stick together. What speed do they move at after the collision?

Mass = 1000kg

Mass = 800kg

Speed = 50m/s Speed = 20m/s

Momentum before = momentum after…

…so 1000 x 50 + 800 x 20 = 1800 x V…

…V = 36.7m/s

Mass = 1800kg

Speed = ??m/s

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Momentum in different directionsMomentum in different directionsWhat happens if the bodies are moving in opposite directions?

Speed = 50m/s

Mass = 1000kg

Speed = 20m/s

Mass = 800kg

Momentum is a VECTOR quantity, so the momentum of the second car is negative…

Total momentum = 1000 x 50 – 800 x 20 = 34000 kgm/s

Speed after collision = 34000 kgm/s / 1800 = 18.9m/s

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Another exampleAnother example

Consider the nuclear decay of Americium-241:

Am24195

α42

If the new neptunium atom moves away at a speed of 5x105 m/s what was the speed of the alpha particle?

Np23793

2.96x107 m/s

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More questions…More questions…1. A car of mass 1000kg heading up the M1 at 50m/s

collides with a stationary truck of mass 8000kg and sticks to it. What velocity does the wreckage move forward at?

2. A defender running away from a goalkeeper at 5m/s is hit in the back of his head by the goal kick. The ball stops dead and the player’s speed increases to 5.5m/s. If the ball had a mass of 500g and the player had a mass of 70kg how fast was the ball moving?

3. A white snooker ball moving at 5m/s strikes a red ball and pots it. Both balls have a mass of 1kg. If the white ball continued in the same direction at 2m/s what was the velocity of the red ball?

4. A gun has a recoil speed of 2m/s when firing. If the gun has a mass of 2kg and the bullet has a mass of 10g what speed does the bullet come out at?

5.6m/s

70m/s

400m/s

3m/s

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Recap question on momentumRecap question on momentum

1. Matt and Dan are racing against each other over 400m at Sports Day. Matt is running at 8m/s and catches up with Dan who is running at 6m/s. After the collision Matt stops and Dan moves slightly faster. If Matt’s mass is 60kg and Dan’s is 70kg calculate how fast Dan moves after the collision.

2. Bobbie is driving her 5kg toy car around. It is travelling at 10m/s when it hits the back of Heather’s (stationary) leg and sticks to it. Assuming Heather’s leg can move freely and has a mass of 10kg calculate how fast it will move after the collision.

12.9m/s

3.3m/s

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Safety featuresSafety featuresHow do air bags and crumple zones work?

Basically:

1) The change in momentum is the same with or without an airbag

2) But having an airbag increases the time of the collision and therefore reduces the “rate of change of momentum”

3) Therefore the force is reduced

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Force and momentumForce and momentumNewton’s second law of motion says that the force acting on an object is that object’s rate of change of momentum. In other words…

mv-mu

TF

Force = Change in momentum Time(in N)

(in kgm/s)

(in s)

For example, Ronaldo takes a free kick by kicking a stationary football with a force of 40N. If the ball has a mass of 0.5kg and his foot is in contact with the ball for 0.1s calculate:

1) The change in momentum of the ball (its impulse),

2) The speed the ball moves away with

Also called “impulse”

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Example questionsExample questions1) Paddy likes playing golf. He strikes a golf ball with a

force of 80N. If the ball has a mass of 200g and the club is in contact with it for 0.2s calculate a) the change in momentum of the golf ball, b) its speed.

2) Courtney thinks it’s funny to hit tennis balls at Kit. She strikes a serve with a force of 30N. If the ball has a mass of 250g and the racket is in contact with it for 0.15s calculate the ball’s change in momentum and its speed.

3) Tom takes a dropkick by kicking a 0.4kg rugby ball away at 10m/s. If his foot was in contact with the ball for 0.1 seconds calculate the force he applied to the ball.

4) Jenny strikes a 200g golf ball away at 50m/s. If she applied a force of 50N calculate how long her club was in contact with the ball for.

16Kgm/s, 80m/s

4.5Kgm/s, 18m/s

40N

0.2s

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Work doneWork done

When any object is moved around work will need to be done on it to get it to move (obviously).

We can work out the amount of work done in moving an object using the formula:

Work done = Force x distance moved

in J in N in m

E

DF

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Example questionsExample questions1. Hannah pushes a book 5m along the table with a force

of 5N. She gets tired and decides to call it a day. How much work did he do?

2. Courtney lifts a laptop 2m into the air with a force of 10N. How much work does she do? What type of energy did the book gain?

3. Tom does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? What type of energy did the wheelbarrow gain?

4. Dan cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use?

5. Simon drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do?

25J

20J, GPE

4m, KE

50N

2MJ

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Stopping a car…Stopping a car…

Recall our earlier situation regarding stopping distances…

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Energy and PowerThe POWER RATING of an appliance is simply how much energy it uses every second.

In other words, 1 Watt = 1 Joule per second

E

TP

E = Energy (in joules)

P = Power (in watts)

T = Time (in seconds)

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Some example questions1) What is the power rating of a light bulb that transfers

120 joules of energy in 2 seconds?

2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds?

3) Rob runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating?

4) How much energy does a 150W light bulb transfer in a) one second, b) one minute?

5) Jonny’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute physics lesson?

6) Lloyd’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day?

60W

2KW

150J, 9KJ

120KJ

1.73MJ

0.2MW

19/04/23Gravitational Potential Energy

To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…

GPE = Weight x Change in height

(Joules) (newtons) (metres)

GPE

Hmg

(Remember - W=mg)

19/04/23Some example questions…How much gravitational potential energy have the

following objects gained?:

1. A brick that weighs 10N lifted to the top of a house (10m),

2. A 1,000kg car lifted by a ramp up to a height of 2m,

3. A 70kg person lifted up 50cm by a friend.

How much GPE have the following objects lost?:

1. A 2N football dropping out of the air after being kicked up 30m,

2. A 0.5N egg falling 10m out of a bird nest,

3. A 1,000kg car falling off its 200cm ramp.

100J

20KJ

60J

5J

20KJ

350J

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Kinetic energyKinetic energyAny object that moves will have kinetic energy.

The amount of kinetic energy an object has can be found using the formula:

Kinetic energy = ½ x mass x velocity squared

in J in kg in m/s

KE = ½ mv2

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Example questionsExample questions

1) Bex drives her car at a speed of 30m/s. If the combined mass of her and the car is 1000kg what is her kinetic energy?

2) Emma rides her bike at a speed of 10m/s. If the combined mass of Emma and her bike is 80kg what is her kinetic energy?

3) Rob is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running?

4) Josh is walking to town. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass?

450,000J

4000J

5m/s

75kg

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Stopping a car…Stopping a car…

What happens inside the car when it stops?

In order to stop this car the brakes must “do work”. This work is used to reduce the

kinetic energy of the vehicle and the brakes will warm up.

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An example question…An example question…

15m/s = 11.25m stopping distance

30m/s = 45m stopping distance (4 times greater)

This car can apply a maximum braking force of 10,000N. If the car’s

mass is 1000Kg how far is its stopping distance when it is

travelling at a speed of 15m/s (roughly 30mph) and 30m/s (roughly

60mph)?

19/04/23A Practical Example of Doing Work

Consider a rocket re-entering the Earth’s atmosphere:

The rocket would initially have a very high _______ energy. This energy would then _____ due to friction caused by collisions with _______ in the atmosphere. These collisions would cause the rocket to ____ up (_____ is “being done” on the rocket). To help deal with this, rockets have special materials that are designed to lose heat quickly.Words – work, kinetic,

particles, heat, decrease

19/04/23Energy Changes in Roller Energy Changes in Roller CoastersCoasters1) Electrical energy is

transferred into gravitational potential energy

2) Gravitational potential energy is transferred into kinetic energy

3) Kinetic energy is transferred back into gravitational potential energy

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Test questions…Test questions…1) Julia tries to run 100m in 12 seconds and succeeds. How

fast did she run?

2) Isabelle accelerates at a rate of 2m/s2 for 3 seconds. If she started at 10m/s what was her final speed?

3) Jake decides to lift his book up into the air. His book has a mass of 100g and he lifts it 50cm. Calculate the work done.

4) Jamie accelerates from 0 to 10m/s in 5 seconds. If her mass is 60kg how much force did her legs apply?

5) Lily rides 1km at a speed of 20m/s. How long did the journey take?

6) Rob thinks it’s funny to push Jack with a force of 140N. If Jack has a mass of 70kg calculate his acceleration.

7) Vicky slams on the brakes on her bike and her brakes do 20,000J of work. If the combined mass is 100kg what speed was she travelling at?

8) Paddy has a mass of 75kg. If he accelerates from 10 to 20m/s in 2s how much force did he apply?

8.3m/s

16m/s

120N

50s

2m/s2

0.5J

20m/s

375N

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Test questions…Test questions…9) Bex amuses herself by throwing things at Kit. If she throws a

ball with a speed of 20m/s and the distance between her and Kit is 5m how long will it take to reach him?

10) Dave throws calculators around the room with a force of 20N. If each calculator has a mass of 200g calculate the acceleration.

11) Max has a mass of 70kg. What is his weight on Earth, where the gravitational field strength is 10N/kg?

12) Kathryn does some work by pushing a box around with a force of 1N. She does 5J of work and decides to call it a day. How far did she push it?

13) On the moon Jake might weigh 112N. If the gravitational field strength on the moon is 1.6N/kg what is his mass?

14) Heather likes bird watching. She sees a bird fly 100m in 20s. How fast was it flying?

15) How much kinetic energy would Simon have if he travelled at a speed of 5m/s and has a mass of 70kg?

0.25s

100m/s2

5m

70kg

5m/s

700N

875J

19/04/2319/04/23Topic 5 – Nuclear Fission and Nuclear FusionTopic 5 – Nuclear Fission and Nuclear Fusion

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The structure of the atomThe structure of the atomELECTRON –

negative, mass nearly

nothing

PROTON – positive,

same mass as neutron

(“1”)

NEUTRON – neutral,

same mass as proton

(“1”)

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The structure of the atomThe structure of the atom

Particle Relative Mass Relative Charge

Proton 1 +1

Neutron 1 0

Electron 1/2000 (i.e. 0) -1

NUCLEON/MASS NUMBER = number of protons + number of

neutrons

SYMBOL

ATOMIC/PROTON NUMBER = number of protons (obviously)

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Introduction to RadioactivitySome substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation at random intervals:

Radiation

The nucleus is more stable after emitting some radiation – this is called “radioactive decay”. This process is NOT affected by temperature or other physical conditions.

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IonisationRadiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons:

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Types of radiationTypes of radiation

1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom)

2) Beta () – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle.

3) Gamma – after or decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed.

Unstable nucleus

Unstable nucleus

Unstable nucleus

New nucleus

New nucleus

New nucleus

Alpha particle

Beta particle

Gamma radiation

Words – frequency, proton, energy, neutrons, helium, beta

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Blocking RadiationEach type of radiation can be blocked by different materials:

Sheet of paper (or 6cm of air

will do)

Few mm of aluminium

Few cm of lead

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SummaryProperty Alpha Beta Gamma

Charge

Mass

Penetration ability

Range in air

What is it?

Ionising ability

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Nuclear power stationsNuclear power stationsNuclear fission reactions can be a source of energy, like in a nuclear power station:

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Nuclear fissionNuclear fission

Uranium or

plutonium nucleus

Unstable

nucleus New nuclei (e.g. barium

and krypton)

More neutron

s

Neutron

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Chain reactionsChain reactions

Each fission reaction releases neutrons that are used in further reactions.

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Nuclear power stationsNuclear power stations

Notice that the heat from these reactions is used to heat water and turn it into steam, which then drives turbines.

Fission in Nuclear power stations

These fission reactions occur in the fuel rods and they become very hot.

Water cools the rods (which then turns to steam) and the control rods (made

of boron) are moved in and out to control the amount of fission reactions

taking place. This is called a Pressurised Water Reactor (PWR)

How are control rods used to control the rate of these reactions?

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Nuclear Fusion in starsNuclear Fusion in starsProton Neutron

Nuclear fusion basically combines smaller nuclei to make larger nuclei. It happens in stars but it’s not possible to use it in power stations yet as it needs temperatures of around 10,000,000OC. At lower

temperatures, electrostatic repulsion of protons occurs (i.e. they repel each other due to their positive charges).

Cold FusionCold Fusion19/04/23

Stanley Pons and Martin Fleishmann

In 1989 we claimed that we had enabled “cold fusion”, i.e. we had created fusion reactions in lab temperatures. However, no one else could verify our findings so our theories have not been accepted.

Topic 6 – Advantages and Topic 6 – Advantages and Disadvantages of using Radioactive Disadvantages of using Radioactive

MaterialsMaterials

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Background RadiationBackground Radiation

Radon gas

Food

Cosmic rays

Gamma rays

Medical

Nuclear power

13% are man-made

Notice that the amount of radon gas in the atmosphere varies according to location so some areas in the UK are

more radioactive than others!

19/04/23Background Radiation by Location

In 1986 an explosion occurred at the Chernobyl nuclear power plant. Here is a “radiation map” showing the background radiation immediately after the event:

Other “risky” areas could be mining underground, being in a plane, working in an x-ray department etc

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Uses of radioactivity 1

Sterilising medical instruments

Gamma rays can be used to kill and sterilise germs without the need for heating. The same technique can be used to kill microbes in food so that it lasts longer.

19/04/23Uses of radioactivity 2 - Tracers

A tracer is a small amount of radioactive material used to detect things, e.g. a leak in a pipe:

Gamma source

Tracers can also be used in medicine to detect tumours:

The radiation from the radioactive source is picked up above the ground, enabling the leak in the pipe to be detected.

For medicinal tracers, you would probably use a beta source with a short half life – why?

19/04/23Uses of radioactivity 3 – Smoke Detectors

Smoke detectors

Alarm

+ve electrode -ve

electrode

Alpha emitter

Ionised air particlesIf smoke enters here a current no longer flows

Uses of radioactivity 4 – Determining thickness

Rollers

Beta emitter

Beta detector

Paper

19/04/23Uses of Radioactivity 5 - Treating Cancer

High energy gamma radiation can be used to kill cancerous cells. However, care must be taken in order to enure that the gamma radiation does not affect normal tissue as well.

Radioactive iodine can be used to treat thyroid cancer. Iodine is needed by the thyroid so it naturally collects there. Radioactive iodine will then give out beta radiation and kill cancerous cells.

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A radioactive decay graph

Time

Activity (Bq) “1 Becquerel” means “1 radioactive count per

second”

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Half life

The decay of radioisotopes can be used to measure the material’s age. The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay…

At start there are 16 radioisotope

s

After 1 half life half have

decayed (that’s 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

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A radioactive decay graph

Time

Count

1 half life

1 half life

1 half life

19/04/23Dating materials using half-livesQuestion: Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample.

8

8

Answer: The sample was originally completely uranium…

…of the sample

was uranium

4

8

2

8

1

8Now only 4/8 of

the uranium remains – the

other 4/8 is lead

Now only 2/8 of uranium

remains – the other 6/8 is

lead

Now only 1/8 of uranium

remains – the other 7/8 is

leadSo it must have taken 3 half lives for the sample to decay until only 1/8 remained (which means that there is 7 times as much lead). Each half life is 4,000,000,000 years so the sample is 12,000,000,000 years old.

1 half life later…

1 half life later…

1 half life later…

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An exam question…

Potassium decays into argon. The half life of potassium is 1.3 billion years. A sample of rock from Mars is found to contain three argon atoms for every atom of potassium. How old is the rock?

(3 marks)

The rock must be 2 half lives old – 2.6 billion years

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IonisationRadiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons:

Alpha radiation is the most ionising (basically, because it’s the biggest). Ionisation causes cells in living tissue to mutate, usually causing cancer.

Understanding Radioactivity over History

Task: Find out about the work of Marie Curie, including:

1) Which elements she discovered

2) Brief details of the work she did

3) What prizes she won

4) How her work eventually caused her death

5) How our understanding of radioactivity has changed due to her work

Disposing of radioactive waste

High level waste is immobilised by mixing with ____ making ingredients, melting and pouring the glass into steel containers.

Intermediate waste is set in cement in _____ drums.

The key to dealing with radioactive waste is to IMMOBILISE it. There are a number of ways of doing this depending on how __________ the waste is:

The containers are then kept in stores, often _________.

Words – glass, steel, underground, radioactive

Nuclear Power StationsAdvantages Disadvantages

Don’t produce greenhouse

gases

Low levels of waste

Low fuel costs

More jobs for local people

Risk of accident

Radioactive waste

Visual pollution

More traffic

Why use nuclear power?