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TAKS Objective 5
Motion , Forces
and Energy
Energy
Is defined as the Ability to do Work
Energy has Two
Types: Kinetic (Energy of Motion) Kinetic (Energy of Motion) and and Potential (Stored Energy)Potential (Stored Energy)
Kinetic Energy
KE = ½ m v 2 Ex: A moving car
has the ability to
do work on the light pole if it hits it.
Gravitational Potential Energy
or Will it fall?
GPE = m g h
m is the mass of the
object in Kg,
g is the acceleration
due to gravity which is
9.8 m/s2 on earth and
h is the height in meters
Use the formula page! PE = mgh
41 What is the potential energy of the rock?
A 59,900 joules
B 64,600 joules
C 93,100 joules
D 121,600 joules
m = 95 kg g = 9.8 m/s2 h = 100 m
95 kg x 9.8 m/s2 x 100 =
93,100 joules C
Electrical Energy - Moving electrons in a path is electricity
Electrical Potential Difference (v) is measured in Volts The rate of moving electric charges, Electric Current
(I), is measured in Amperes Resistance or opposition to the movement of the
energy is called Resistance (R).
Circuits – 2 types
Series circuits are the most simple.
One (1) path for the current to travel.
Contains an energy source, a path, and a load (something for it to do, like a lamp)
Circuits – 2 types Parallel circuits
provide more than one path for the current to travel.
Most circuits are parallel, since if one lamp goes out, the others can stay lit.
F. QG. RH. SJ. T
6. Which switches, if opened, will cause the light bulb to stop
glowing?
It is the only switch in series to both the battery and light.
USE THE FORMULA SHEET!!
What is the current in a copper wire that has a resistance of 2 ohms and is connected to a 9 volt electrical source?
A. 0.22 amp
B. 4.5 amps
C. 11.0 amps
D. 18.0 amps
V = I R so,
9V = I x 2 ohms or 4.5 amps
Heat- Transfer of Thermal Energy
1. Conduction-direct contact, a pot heating on a stove (solids)
2. Convection- heating by circulating fluids, (gas and liquid) heating from a fireplace
And. . .
Three forms of heating:Three forms of heating:
3. Radiation – Transfer of Electromagnetic (E.M.) Energy
Objects are heated when exposed to infrared radiation
The suns heats the earth by sending infrared radiation along with other forms of E.M. energy 3.0 x 108 meters through empty space
Heat moves by conduction in solids since the particles are close together and vibrate. . .
43 Heat convection occurs in gases and liquids. Heat convection does not occur in solids because solids are unable to —
A absorb heat by vibrating
B transfer heat by fluid motion
C emit radiation by reflecting light
D exchange heat by direct contact
Solids do radiate heat to their surroundings
2 The primary way liquids and gases transmit heat is by the process of —
F reflection
G conduction
H radiation
J convection
Fluid heat movement is convection. Fluid motion occurs in liquids and gases.
F improve emission of infrared radiation
G reduce the heat loss by convection currents
H improve absorption of infrared radiation
J reduce the heater’s conducting properties
50 A solar heater uses energy from the sun to heat water. The heater’s panel is painted black to —
Emission is giving off – we want to absorb: Not F
Convection is movement of heat in fluid matter, heat loss would be from a solid exterior – Not GPainting a substance will not change its conductivity
– That is a property of metals. It would have to be made of a different substance to change that: Not J
Waves - Energy carried by rhythmic disturbances
Two types: 1. E.M. radiation
move through empty space
2. Mechanical require a medium (air, water or any type of matter) for movement
Waves - 2 Types
All waves have similar properties
Frequency- the number of vibrations per second or the speed of the movement of the vibrating particles
Amplitude – the size of the movement of the vibrating particles
Both are controlled by the disturbance that created the waves
Velocity of all waves - v=f λ
f-frequency and λ is wavelength (distance between identical points on two consecutive waves)
Reflection- bounce off barriers in regular ways
Refraction- waves can change direction when speed changes
And the answer is?
38 At 0°C sound travels through air at a speed of 330 m/s. If a sound wave is produced with a wavelength of 0.10 m, what is the wave’s frequency?
F 0.0033 Hz
G 33 Hz
H 330 Hz
J 3300 Hz
Use the formula chart!!!
Velocity = f λ OR f λ OR
330 m/s = f x 0.10 m330 m/s = f x 0.10 m
JJ 3300 Hz 3300 Hz
Sound Waves move through matter not through empty space.
32 One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because of —
F interference
G the Doppler effect
H resonance
J standing waves
Resonance is the vibration of another object struck by a wave of the correct frequency. Since the forks are identical, the second one receives the correct frequency to begin vibrating.
Forces and Motion Forces can create
changes in motion (acceleration)
Deceleration is negative acceleration
Velocity Graphs V = distance
time
Velocity (v) is the slope (rise over run) of a position (d) vs. time (t) graph
Velocity
0
20
40
60
1 3 5 7 9 11 13 15
Time (sec)
Dista
nce (
m) Series1
Series2
40 The diagram represents the total travel of a teacher on a Saturday. Which part of the trip is made at the greatest average speed?F QG RH SJ T
How do we work this one?
Calculate v = d/t for each segment.
Acceleration Graphs Acceleration (a) is
the slope of a velocity (v) vs. time (t) graph
Plotted on a distance vs. time graph, acceleration is an exponential curve
Acceleration
0
20
40
60
1 3 5 7 9 11 13 15
Time (sec)
Velo
city
((m
/s)(m
)
Acceleration is a change in an objects velocity (speed or direction)
When an object’s speed changes over time it is accelerating (or decelerating)
A = vfinal – vinitial time Units for acceleration
m/s/s or m/s2
Definition of a Force
A Force is a push or a pull
Balanced Force
A force that produces no change in an object’s motion because it is balanced by an equal, opposite force.
4 The picture shows the position of a ball every 0.25 second on a photogram. Using a ruler, determine the velocity of the ball.
F 3.5 cm/s
G 10.5 cm/s
H 14.0 cm/s
J 28.0 cm/s
Use the ruler on the side of the chart and the equation for velocity. The answer was H.
Measure from the center of ball 1 to the center of ball 2 and divide by .25.
Unbalanced Forces
Are forces that results in an object’s motion being changed.
+
Friction
A force that acts in a direction opposite to the motion of two surfaces in contact with each other.
Friction
Friction causes an object to slow down and stop.
Since the amount of energy stays constant, the energy becomes heat.
Newton’s 1st Law of Motion
Object in motion stays in motion
Newton’s 1st Law of Motion
And Objects at rest stay at rest
Newton’s 1st Law of Motion
Until they are acted upon by unbalanced forces.
Inertia or Newtons 1st Law
Tendency for an object to stay at rest or moving in a straight line at a constant speed.
The mass (m measured in kg) of an object determines its inertia
Newton’s 2nd Law of Motion
Force = Mass X AccelerationF=maWeight (pull of gravity) is a commonly measured force,
calculated by F=mg, g is the acceleration due to gravity 9.8 m/s2
Newton’s 2nd Law of Motion
The greater the mass of an object, the greater the force required to change its motion.
Newton’s 2nd Law of Motion
The greater the acceleration of an object, the greater the force required to change its motion.
A 0.2 N B 0.8 N C 1.5 N D 6.0 N
11 The frog leaps from its resting position at the lake’s bank onto a lily pad. If the frog has a mass of 0.5 kg and the acceleration of the leap is 3 m/s2, what is the force the frog exerts on the lake’s bank when leaping?
Formula chart says F=ma, m is mass in kg, a is acceleration in m/s2.
So, .5 kg x 3 m/s2= 1.5 N
Newton’s 3rd Law of Motion
For every action force there is an equal and opposite reaction force.
Newton’s 3rd Law of Motion
All forces come in action-reaction pairs
Ex: feet push backward on floor, the floor pushes forward on feet
27 A ball moving at 30 m/s has a momentum of 15 kg·m/s. The mass of the ball is —
A 45 kg
B 15 kg
C 2.0 kg
D 0.5 kg
Formula Page says that Momentum = Mass x Velocity
So 15 kg.m/s = M x 30 m/s solving for M it is:
Work Work: using a force
for a distance W = F x d The work done by forces on an object
= changes in energy for that object. Work and Energy are measured in
Joules 1 Joule=1 Newton • meter
42 How much work is performed when a 50 kg crate is pushed 15 m with a force of 20 N?
F 300 JG 750 JH 1,000 JJ 15,000 J
Use the formula Work = Force x distance
Force of 20 N x 15 meters = 300 Joules Answer:
Machines make work easier
The ideal mechanical advantage of a machine (IMA) of a machine is the number of times the output force is larger than the input
force IMA=Fout/Fin A machine can only make this
happen by moving the input force through a farther distance than the output force
Fin • din=Fout • dout
48 The diagram shows an electric motor lifting a 6 N block a distance of 3 m. The total amount of electrical energy used by the motor is 30 J. How much energy does the motor convert to heat?
F 9 J
G 12 J
H 18 J
J 21 J
Work Output = Resistance Force x Resistance Distance
Workout = 18J = 6N x 3m
Work Input = 30J done by the motor
The difference is lost as heat due to friction, which is 30J – 18J = 12J
Answer G
Real Machines use Energy No real machine is
100 % efficient. i.e. none put out more work than is put in
Efficiency of a machine is work output/work input X 100 %
Eff = Wout X 100%
Win
Machines use power Power: the rate at
which energy is used (work is done)
P=Work/time Power is measured in
H.P. or watts 1 watt = 1 Joule
1 sec
A accelerated rapidly
B remained motionless
C decreased its velocity
D gained momentum
45 If a force of 100 newtons was exerted on an object and no work was done, the object must have —
Work = Force x Distance
Work = 0 Force = 100 N so
0 J = 100 N x d
distance must be 0
It did not move!
Universal Law of Gravitation
All objects in the universe attract each other by the force of gravity
Universal Law of Gravitation
Gravity varies depending on two factors:
1) the mass of the object doing the pulling, and
2) the distance from the center of that object
On Earth gravity = 9.8 m/s/s
For every second that an object falls its speed increases by 9.8 m/s
Weight= Mass (m) X gravity (g)
Weight Unit of mass = kg Unit of acceleration =
m/s/s Unit of weight = Newton 1 Newton= about ¼ pound