Forces, Waves and Electricity26%

Speed and Velocity

Speed = distance divided by time

s = d/t Units of speed = m/s Velocity = speed in a given direction Example:

55 mph = speed 55 mph north = velocity

Acceleration

Acceleration = rate at which velocity changes Involves a change in speed OR direction

a = (vf – vi )/ t Units of acceleration = m/s2

Example: 0 to 60 mph in 5 seconds For acceleration to occur a net

(unbalanced) force must be applied

Sample Question #1

Use the equations for velocity and acceleration to solve the following examples: A ball rolls in a straight line very slowly across the

floor traveling 1.0 meter in 2.0 seconds. Calculate the velocity of the ball. Answer: v = 0.50 m/s

If the ball from the above question rolls to a stop in 2.0 seconds, calculate the acceleration (deceleration) of the ball. Answer: a = -0.25 m/s2

Newton’s 1st Law of Motion An object at rest will

remain at rest and an object in constant motion will remain in constant motion unless acted on by an unbalanced force.

Reason for seatbelts

Newton’s 2nd Law of Motion Force = mass x acceleration

F = ma

Newton’s 3rd Law of Motion

For every action, there is an equal but opposite reaction

Examples: Punch a wall, it

punches back Rocket propulsion

Mass- stays the same

Weight- changesgravity decreases, weight decreases

Mass- stays the sameMass- stays the same

Weight- changesWeight- changesgravity decreases,gravity decreases, weight decreases weight decreases

Mass is in g, kgMass is in g, kgWeight is is NewtonsWeight is is Newtons

Falling objects and gravity

Force, mass, and acceleration are interdependent. A change in any one of these affects the others.

Friction is an ever present force that opposes motion.

All objects fall at the same speed independent of its mass if there are not frictional forces acting upon them.

Falling objects and gravity

An astronaut on the moon drops a feather and a rock from the same height. They reach the ground at the same time. Why does this happen on the moon but NOT on Earth?

The moon has no atmosphere. The moon’s weaker gravity pulls each with less

force. Objects dropped on Earth are not influenced by

lunar gravity. On Earth, the rock has more mass due to Earth’s

stronger gravity

Energy and Work Energy = The ability to do work Work = transfer of energy by applying a

force to move an object

W = Fd

where force and distance are in same direction

Both work and energy are measured in Joules(J)

Static Equilibrium

If the combined effect of all the forces acting on a body is zero and the body is in the state of rest then its equilibrium is termed as static equilibrium.

Examples of Work and No Work

Hammer applies a force to move the nail in the same direction = WORK

Waiter applies a force upward while the tray moves forward = NO WORK

Types of Mechanical Energy

Kinetic = energy of motion

Potential = stored energy due to position

Light

Light is a form of electromagnetic radiation (EM) EM spectrum shows the forms of radiation in order

of increasing frequency (and energy) and decreasing wavelength

Electromagnetic Wave (EM) versus Mechanical Wave

EM WAVE does not require

matter to transfer energy

CAN travel through a vacuum

example: light

MECHANICAL WAVE does require matter to

transfer energy CANNOT travel

through a vacuum example: sound

A scientist investigates the type of radiation being emitted by a radioactive sample. An apparatus is constructed using a radiation detector, a radioactive sample, and two different types of absorbers placed between the detector and the sample.

Absorber used Average counts per second

No absorber 33

Paper 1 mm thick 20

Metal 3 mm thick 1

Question

Which type(s) of radiation does the sample emit?

A. The sample emits alpha radiation. B. The sample emits beta radiation. C.*The sample emits both alpha and beta

radiation. D. The sample emits neither alpha nor beta

radiation.

vacuum of space

Light but NO sound

Speed of Sound

solidliquid

gas

emptyspace

fastest

slowestnone

Thunder

thunder and lightningL then T

Light faster than Sound

Thunder & lightningL then T

Light faster than sound

Reflection of Light

When light strikes a boundary, it reflects.

The angle at which the wave approaches a flat reflecting surface is equal to the angle at which the wave leaves the surface (like a bounce pass of a basketball).

Reflection results in image formation.

Refraction of Light Light waves travel

faster in air than in water and slower in glass than water.

More dense = slower light

When light enters a different medium, speed changes and it bends.

Bending of light due to change in speed = REFRACTION

refraction

Wave Interference

the phenomenon which occurs when two waves meet while traveling along the same medium

constructive = waves add to produce a larger wave

destructive = waves cancel to produce a smaller wave

CONSTRUCTIVE

DESTRUCTIVE

This diagram shows two overlapping waves with the same wavelength and amplitude.

Which statement correctly explains the diagram?

A. The waves overlap and increase in frequency.

B. The wave frequencies overlap and increase refraction.

C. Diffraction between the waves increases the amplitude.

D. Interference between the waves increases the amplitude.

Which diagram represents interference?

Doppler Effect

Increase frequency, Decrease frequencyincoming departing

Electricity Electrons carry a negative charge. Lost electrons = positive charge Gained electrons = negative charge REMEMBER:

Like charges repel Opposites attract

Ohm’s Law and electricity

In a direct current (DC) circuit, the relationship between the current (I) passing through a resistor, the potential difference (V) across the resistor, and the resistance (R ) of the resistor is described by Ohm’s Law:V = IR.

Find this formulaOn your Formula Sheet

Direct Circuits (DC)

The force motivating electrons to "flow" in a circuit is called voltage. Voltage is a specific measure of potential energy that is always relative between two points

Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance

The "I" is thought to have been meant to represent "Intensity" (of electron flow)

What is the amount of voltage provided by the battery?

V= IR V= (2A) X 7 V=14

Practice

What formula do you use? How many volts is in this circuit? How many Ohms? How much current?

Electrical Circuits

Current flows in a closed circuit

Ohm’s Law V = IR

Two types of circuits: Series (single path)-

Christmas tree lights Parallel (many paths)-houses

SERIES

PARALLEL

Permanent Magnets

Stronger: more loops stronger battery

ELECTROMAGNET

.

“Mag”nificent Information

Even the most powerful permanent magnet is not as strong as the stronger electromagnets, so their applications are limited, but they still have many uses.

Magnets can be found everywhere, including your computer, ATM and credit cards, speakers and microphones, electric motors, and toys.

Electric motors work through an interaction between an electromagnet and a permanent magnet

Waves – Hertz – frequency

Electricity

Volts- Potential Difference Voltage V Amps- Current A Ohms- ResistanceΩ

Remember to…. 1.WRITE DOWN

WHAT YOU KNOW BEFORE YOU START!!!!

2.Take your time3.Guess if you need to