Download EOCT Review Physics – Energy, Force, and Motion

Physical Science EOCT Review
Physics – Energy, Force and Motion
To meet standards, students should be able to:
1) Identify the types, sources and uses of energy (chemical, thermal, mechanical, thermonuclear,
photoelectric and electromagnetic)
2) Trace the transformation of energy within a given system
3) Relate molecular motion to the thermal energy changes in conduction, convection and radiation
4) Recognize the role of conductors and insulators in the transfer of heat
5) Calculate the heat lost or gained by a system, given mass, specific heat capacity and temperature change
6) Using a phase diagram, explain the changes in matter within a system, as it relates to pressure and
temperature
7) Calculate velocity of an object, given the displacement and time of measurement for that object
8) Calculate acceleration of an object, given the change in velocity and time for that object
9) Define inertia and recognize common examples of inertia
10) Measure and analyze the effects of balanced and unbalanced forces on an object in motion
11) Recognize the relationship between force mass and acceleration, as described in Newton’s second law
12) Solve application problems involving force, mass or acceleration of an object demonstrating an
understanding of Newton’s second law
13) Calculate the force of an object, given the mass and the acceleration of that object
14) Recognize and determine the outcome of common examples of Newton’s third law
15) Identify common forces, including friction
16) Relate falling objects to gravitational force
17) Contrast mass and weight
18) Calculate the work and mechanical advantage of a simple machine
Thermal Energy
All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules in
constant motion. Because of this constant motion, all atoms have thermal (heat) energy. Whenever a
substance is heated, the atoms move faster and faster. When a substance is cooled, the atoms move slower
and slower. The "average motion" of the atoms that we sense is what we call temperature.
Temperature and heat ARE NOT technically the same thing. Temperature is the average motion of atoms
and molecules. Heat is the energy that flows due to temperature differences. Heat is always transferred
from warmer to cooler substances.
There are three ways to heat the atmosphere (or anything else, for that matter). These ways include
conduction, convection, and radiation. How can you remember these? Let’s use an analogy to help you
figure this out.
There are three ways to cook popcorn.
1. Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the pan on
the stove and turn on the burner to medium heat. Cover the pan with a lid. Periodically shake the
pan so the kernels move around in the oil.
2. Obtain a popcorn popper. Place the popcorn kernels in the popper. Plug in/turn on the popper. Hot
air will transfer heat to the kernels, making them expand and pop.
3. Microwave a bag of microwave popcorn.
Each of these methods of cooking popcorn is really an example of the three ways heat can be
transferred.
1. Conduction. This method of heat transfer is most familiar to people. If you have ever burned
yourself on a hot pan because you touched it, you have experienced this first-hand. Conduction is
heat transfer through matter. Metals conduct heat well. Air is not as good a conductor of heat. This
is a direct contact type of heat transfer. The only air heated by the Earth is the air at the Earth’s
surface. As a means of heat transfer, conduction is the least significant with regard to heating the
Earth’s atmosphere. Which popcorn example does it relate to? #1. The heat is transferred by direct
contact from the pan, to the oil, to the kernels of popcorn..
2. Convection. Convection is heat transfer by the movement of mass from one place to another. It
can take place only in liquids and gases. Heat gained by conduction or radiation from the sun is
moved about the planet by convection. The radiation from the sun heats the air of the atmosphere,
but the heating of the Earth is not even. This is because the amount of sunlight an area receives
depends upon the time of day and the time of year. In general, regions near the equator have hotter
air. This hot air rises, allowing cooler air to move in underneath the warm air. In our popcorn
example this relates to #2. The hot air transfers the heat to the cooler kernels, and when enough
hot air heats the kernels they pop.
3. Radiation is the only way heat is transferred that can move through the relative emptiness of
space. All other forms of heat transfer require motion of molecules like air or water to move heat.
The majority of our energy arrives in the form of radiation from our Sun. Objects that are good
absorbers of radiation are good radiators as well. The atmosphere, which does not absorb certain
wavelengths of solar radiation, will absorb certain wavelengths of radiation. The particles that
reach Earth from the Sun are within a wavelength that the Earth’s atmosphere will absorb. When
the Sun heats the Earth, the Earth gets warmer in that location and re-radiates heat into the
atmosphere, making it doubly warm. This relates to popcorn example #3. The kernels are heated
by the radiation in the microwave, and the kernels heat up, giving off more heat to the kernels
surrounding it and making it "doubly warm."
Conductors and Insulators
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Heat passes through some materials easily and these materials are called thermal conductors.
Metals usually feel cold to the touch. Metals are good thermal conductors, because heat passes
through them quickly.
Heat does not pass through some material such as plastic, oven glove, thermal underwear, cork board
and wood. These materials are called thermal insulators.
These thermal insulators are good for keeping heat out as well and in. Some examples of good
insulators are - a thermos - keeps hot things hot and keeps cold things cold, cooler - deeps the heat
out and keeps the inside cool, and a polystyrene cup keeps the heat in and keeps it hot.
Remember that a good insulator is a poor conductor.
Heat loves to travel and will travel from a warmer material to a colder material. The heat will only
travel from hot things to colder things and never the other way around.
Some materials allow heat to travel through easily and some don't. If you boil a tea pot on the stove,
the pot becomes too hot to touch and whereas the tea pot handle does not get hot
Specific Heat Capacity
The specific heat capacity of a solid or liquid is defined as the heat required to raise unit mass of
substance by one degree of temperature. This can be stated by the following equation:
where,
Q= Heat supplied to substance,
Mass of the substance,
Specific heat capacity,
T= Temperature rise.
Pressure vs Temperature (PTV)
m=
c=
Phase diagram, a graph that shows the relation between the solid, liquid, and gaseous states of a
substance (states of matter) as a function of the temperature and pressure. The graph is divided into three
regions, one for each of the physical states, and it specifies the range of temperatures at which the
substance exists in each state for any value of the pressure.
P T V
Energy Transformations
Energy transformation is the process of changing energy from one form to another. This process is
happening all the time, both in the world and within people. When people consume food, the body utilizes
the chemical energy in the bonds of the food and transforms it into mechanical energy, a new form of
chemical energy, or thermal energy. Energy transformation is an important concept in the application of
the physical sciences. The ability for energy to be transformed automates, lights, entertains, and warms
the world in an astounding multitude of ways.
The concept of energy transformation can be illustrated in a number of common activities. An engine,
such as the engine in a car, converts the chemical energy of gas and oxygen into the mechanical energy of
engine movement. A light bulb changes the chemical energy of the bulb into electromagnetic radiation, or
light. Windmills harness the energy of the wind and convert it into mechanical energy in the movement of
the turbine blades, which is then converted to electrical energy. Solar panels transform light to electricity.
Energy transformation can also be explained in terms of potential energy, the stored energy of a system,
which can be converted into kinetic energy, the energy of movement. For example, a roller coaster sitting
at the top of a hill is said to have potential energy. This potential energy is gravitational, which is gained
when the coaster moves up the hill. Once the coaster begins to move down the hill, the force of gravity is
exerted and the potential energy is transformed into the kinetic energy of the car moving. During energy
transformations, potential energy is often transformed to kinetic energy and back again to potential
energy.
During any kind of energy transformation, some energy is lost to the environment. As a result of this loss,
no machine is ever 100% efficient. Commonly, a portion of the energy lost during energy transformation
is lost as heat. This can be observed in practice by noting the heat emitted by a computer, a car, or another
type of machine that has been in use for a period of time.
Kinetic Energy
The extra energy that an object possesses when it is in motion is known as kinetic energy. This motion of
the object can be in any possible direction, and there are several different types of motion by which an
object can move.
Mechanical Energy
Mechanical energy is the sum of energy in a mechanical system. This energy includes both kinetic energy,
the energy of motion, and potential energy, the stored energy of position. A mechanical system is any
group of objects that interact based on basic mechanical principles. The energy that a machine exerts is a
type of mechanical energy.
Thermal Energy
Thermal energy or heat is another form of energy. It is a type of kinetic energy since it deals with the
speed or velocity of the particles.
Electromagnetic Energy
The energy source required to transmit information (in the form of waves) from one place (material) to
another. Some types of electromagnetic energy include: radio waves, microwaves, infrared waves, visible
light, ultraviolet light, x-rays, and gamma rays. All electromagnetic forms of energy travel at the speed of
light which is very fast.
Potential Energy
Potential energy is the stored energy of position. It can be thought of as energy that is “stored” by any
physical system. It is called potential because, in its current form, it is not doing any work or causing any
change in its surroundings. It does, however, have the potential to be converted to different forms of
energy, such as kinetic energy.
Chemical Energy
Scientifically, energy is defined as the ability to do work. While there are many forms of energy, they can
be grouped into two categories: potential energy, or stored energy; and kinetic energy, or energy of
motion. Chemical energy is a form of potential energy and it is possessed by things such as food, fuels
and batteries.
Gravitational Potential Energy
Gravitational potential energy is energy stored within an object due to its height above the surface of the
Earth. In order for an object to be lifted vertically upwards, work must be done against the downward pull
of gravity. The amount of energy used to lift the object against gravity is then stored as gravitational
potential energy within the object. When the object is released and falls towards the Earth, the stored
energy is converted into kinetic energy, the energy of movement.
Velocity and Acceleration
An object is in motion when it is continuously changing its position relative to a reference point and as
observed by a person or detection device. For example, you can see that an automobile is moving with
respect to the ground. The distance the object goes in a period of time is its speed. If the speed of an
object is in a specific direction, it is called velocity. The change in velocity over a period of time is the
acceleration of the object.
Speed is how fast an object is going with respect to an object. Velocity is a measure of the speed in a given
direction. You can say the top speed of an airplane is 300 kilometers per hour (kph). But its velocity is
300 kph in a northeast direction.
In order to determine how fast an object is going, you measure the time it takes to cover a given distance,
using the equation
d = vt
where:
d is the distance
v is the speed or velocity
t is the time covered
vt is v times t
From this equation, you can get the equation for velocity as v = d/t. Velocity (v) or speed equals the
distance (d) traveled divided by the time (t) it takes to go that distance.
Example
For example, if a car went 120 miles in 2 hours, its average speed would be the distance of 120 miles
divided by the time of 2 hours equaling 60 miles per hour (mph).
If it takes a car 2 minutes to travel 1 mile, its speed is 1 mile divided by 2 minutes, which equals 1/2 mile
per minute or 30 miles per hour.
If you travel from Milwaukee to Chicago (90 miles) at an average velocity of 60 mph, it would take you
90 mi. ÷ 60 mph = 1.5 hours to travel the distance.
Acceleration
Acceleration is the increase of velocity over a period of time. Deceleration is the decrease of velocity.
When you start running, you accelerate (increase your velocity) until you reach a constant speed.
Mathematically, acceleration is the change in velocity divided by the time for the change
a = (v2 − v1)/(t2 − t1)
where:
 v2 − v1 is the end velocity minus the beginning velocity
 t2 − t1 is the measured time period between the two velocities
Often this is written as a = Δv/Δt, where Δ is the Greek letter delta and stands for difference.
For example, if an object speeds up from a velocity of 240 meters/second to 560 meters/second in a time
period of 10 seconds, the acceleration is (560 - 240)/10 = 320/10 = 32 m/s/s or 32 m/s².
Changing direction can also cause acceleration (or deceleration) because the velocity in that direction has
changed.
Newton’s Laws of Motion
Three Laws of Motion
 Newton's First Law of Motion states that in order for the motion of an object to change, a force
must act upon it, a concept generally called inertia. Inertia is the name for the tendency of an
object in motion to remain in motion, or an object at rest to remain at rest, unless acted upon by a
force.
The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in
motion, with the same direction and speed. Motion (or lack of motion) cannot change without an
unbalanced force acting. If nothing is happening to you, and nothing does happen, you will never go
anywhere. If you're going in a specific direction, unless something happens to you, you will always go in
that direction. Forever.
You can see good examples of this idea when you see video footage of astronauts. Have you ever noticed
that their tools float? They can just place them in space and they stay in one place. There is no interfering
force to cause this situation to change. The same is true when they throw objects for the camera. Those
objects move in a straight line. If they threw something when doing a spacewalk, that object would
continue moving forever in the same direction and with the same speed unless interfered with by another
force, such as another planet's gravity pulled on it.
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Newton's Second Law of Motion defines the relationship between acceleration, force, and mass.
As the mass goes up, the same force will cause an object to have less acceleration. This law is
often stated mathematically as F= mass x acceleration.
The second law says that the acceleration of an object produced by
a net (total) applied force is directly related to the magnitude of the
force, the same direction as the force, and inversely related to the
mass of the object (inverse is a value that is one over another
number... the inverse of 2 is 1/2). The second law shows that if you
exert the same force on two objects of different mass, you will get
different accelerations (changes in motion). The effect (acceleration)
on the smaller mass will be greater (more noticeable). The effect of a
10 Newton force on a baseball would be much greater than that same
force acting on a truck. The difference in effect (acceleration) is
entirely due to the difference in their masses.
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Newton's Third Law of Motion states that any time a force acts from one object to another, there is
an equal force acting back on the original object. If you pull on a rope, therefore, the rope is pulling
back on you as well.
The third law says that for every action (force) there is an equal and opposite
reaction (force). Forces are found in pairs. Think about the time you sit in a
chair. Your body exerts a force downward and that chair needs to exert an equal force upward or the chair
will collapse. It's an issue of symmetry. Acting forces encounter other forces in the opposite direction.
There's also the example of shooting a cannonball. When the cannonball is fired through the air (by the
explosion), the cannon is pushed backward. The force pushing the ball out was equal to the force pushing
the cannon back, but the effect on the cannon is less noticeable because it has a much larger mass. That
example is similar to the kick when a gun fires a bullet forward.
Forces and Gravitation
Gravity is a term used for gravitation for objects relatively close to Earth. Gravitation is the force
that attracts bodies of matter toward each other, often at great distances. Gravity is the force that pulls
objects toward the Earth.
The equation for the force of gravity is F = mg. The major result of this force is that all objects fall
at the same rate, regardless of their mass. Gravity on the Moon and on other planets have different values
of the acceleration due to gravity, but the effects of the force are similar.
Acceleration due to gravity
The acceleration due to the force of gravity on Earth is g:
g = 9.8 m/s2 in the metric or SI system of measurement
g = 32 ft/s2 in the English system of measurement
In the equation F = mg, you must use the same measurement system for mass, m, as you do for g.
Weight
The weight of an object is the measurement of the force of gravity on that object. You weigh
something on a scale, according to the force that the Earth pulls it down:
w = mg
where w is the weight in Newtons (N) or pounds (lb).
Note: There is often confusion concerning the designation of weight and mass. Although a kilogram is
supposed to be a unit of mass, it is often used to designate weight.
The weight of 1 kg of mass is w = 9.8 Newtons.
Objects fall at the same rate
The most outstanding characteristic of gravity is the fact that all
objects fall at the same rate—assuming the effect of air resistance is
negligible. This is because the acceleration due to gravity, g, is a
constant for all objects, no matter what their mass.
This seems opposite to what you would expect. You would
expect a heavy object to fall faster than an object that weighed less. But
it is a fact. Try dropping two objects at the same time, from the same
height, making sure they are heavy enough not to be affected by air
resistance. You will see they hit the ground at the same time.
Mass and Weight
Mass is a measure of how much matter an object has. Weight is a measure of how strongly gravity
pulls on that matter. Thus if you were to travel to the moon your weight would change because the pull of
gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of
the same amount of matter.
Work and Mechanical Advantage
Machines are devices that make work easier. How they do this varies from one machine to another. For
much of human history, machines were powered by either human or animal muscle power. Today most
machines are powered by electricity as in an electric drill, or by some type of engine that burns a fuel, like
a gas powered lawn mower.
The two main types of machines are simple and compound. Simple machines are those able to do work (
w = f • d ) with just one movement of the machine. Compound machines require more than one
movement to do work.
Our focus will be the simple machines, of which there are six basic types. They can be grouped into the
following categories: lever family- the lever, wheel and axle, and pulley/ inclined plane family- inclined
plane, screw and wedge The ways a machine makes work easier is by changing the direction and/or the
size of the force put into the machine. The amount of force you put into a machine is called the effort
force ( Fe ), while the amount of force the machine needs to move something to do work is called the
resistance force ( Fr ).
Speaking of work, when a machine is being used, you must do work on the machine, called the input
work ( Win ), while the machine itself does work, called the output work ( Wout ). The work input can be
determined using the formula Win =Fe x de, where de is the distance the effort force has to move. The work
output is determined in a similar fashion, where Wout =Fr x dr with dr being the distance the resistance
force has to move.
Since a machine has parts that are in contact with other things, friction is produced. So in the real world,
the work input can never be equal to the work output. However, engineers and designers of machines like
to imagine their machines as having no friction. These ideal machines would have the work input equal to
the work output, or Win = Wout. Since machines can’t produce more work than the work put into them,
there has to be a trade off. For example, to lift a 10 Newton weight straight up a distance of 2 meters,
requires 20 Joules of work ( w = f • d ). If the same 10 Newton weight is pulled along an inclined plane it
might only need 2 Newtons of force to pull it, but you would have to pull it for a distance of 10 meters.
The amount that a machine is able to multiply the effort force put into it is called the mechanical
advantage ( MA ). This can be calculated by the following:
MA =Resistance force (Fr)
Effort force (Fe)
Name ________________________________________________date __________period____
Physical Science EOCT Review
Physics – Energy, Force and Motion
Write what energy transformations are taking place in each of the following examples.
1. burning match ___________________________________________________
2. radio___________________________________________________________
3. walking_________________________________________________________
4. solar panels on a space satellite______________________________________
Answer the following questions.
5. How can you increase the amount of kinetic energy in a small ball of clay you are throwing to a
friend?
6. How can you increase the amount of potential energy in a book sitting on a bookshelf?
7. How is energy transferred during convection?
8. Does convection occur in solids? Why or why not?
9. Give three examples of each:
a. Conduction:
i.
ii.
iii.
b. Convection
i.
ii.
iii.
c. Radiation
i.
ii.
iii.
10. The specific heat of water is 4.2 j/g Cº. If it takes 31,500 joules of heat to warm 750 g of water, what
was the temperature change?
11. Explain how kinetic energy and potential energy vary as a girl swings on a playground swing-set.
12. A roller coaster car rapidly picks up speed as it rolls down a slope. As it starts down the slope, its
speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average
acceleration?
13. A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s average acceleration?
14. A car traveled 1025 km frm El Paso to Dallas in 13.5 hr. What was its average velocity?
15.
a. How many meters can Swimmer 1 cover in 30 sec?
___________________________________
b. How far will Swimmer 2 go in 30 sec?
___________________________________
c. Predict the number of m Swimmer 1 can go in 60 sec. ___________________________________
d. Predict the number of m Swimmer 2 can go in 60
___________________________________
sec.
e. Which swimmer has the greatest speed?
___________________________________
f. Calculate the speed of Swimmer 1.
___________________________________
g. Calculate the speed of Swimmer 2.
___________________________________
16. Inertia can best be described as _____.
a. the force which keeps moving objects moving an stationary objects at rest.
b. the willingness of an object to eventually lose its motion
c. the force which causes all objects to stop
d. the tendency of any object to resist change and keep doing whatever its doing
17. A physics book is motionless on the top of a table. If you give it a hard push with your hand, it slides
across the table and slowly comes to a stop. Use Newton’s first law of motion to answer the following
questions:
a) Why does the book remain motionless before the force is applied?
b) Why does the book move when he hand pushes on it?
c) Why does the book eventually come to a stop?
d) Under what conditions would the book remain in motion at a constant speed?
18. Why does a package on the seat of a bus slide backward when the bus accelerates quickly from rest?
Why does it slide forward when the driver applies the brakes?
19. .If you are in a car that is struck from behind, you can receive a serious injury called whiplash.
a) Using Newton’s laws of motion, explain what happens.
b) How does a headrest reduce whiplash?
20. Fill in the end slide in each picture:
a) Explain what happened in the first comic:
____________________________________________________________________________
b) Explain what happened in the second comic:
__________________________________________________________________________
21. The tablecloth trick is an example of “objects at rest tend to stay _______________”.
22. If you slide a hockey puck along an air table (where there is virtually no friction), it slides in a straight
line with no apparent loss in _______________. This is an example of “objects in motion tend to stay
_______________”.
23. All freely falling objects fall with the same ____________________ because the net force on an
object is only its weight, and the ratio of weight to mass is the same for all objects.
24. A 10-kg cannonball and a 1-kg stone dropped from an elevated position at the same time will fall
together and strike the ground at practically the _______________ time.
25. Answer the following questions, using either mass or weight.
a. The amount of matter in an object is called its __________________.
b. The force of gravity on an object is called its ___________________.
c. If you take a spaceship into space, your _______________stays the s
same.
d. If you take a spaceship into space, your _______________changes.
e. The force of gravity when one object has a much larger_____________
than the other object.
f. If you double the mass of an object, you double the object’s ______________.
g. On Earth you can compare the masses of different objects by comparing
their _________________________.
h. __________________ is measured in grams or kilograms.
i. ___________________is measured in Newtons.
26. If you drop a 50cent piece (halfdollar) and a 10 centpiece (a dime) from a tall
building…
a. Do the objects have the same mass? ______________
b.Will both coins hit the ground at the same time? _____________
27. It takes 100 N to pull an object up an inclined plane. The gravitational force on the object is 600 N.
a. What is the load force in this case? ___________________N
b.What is the effort force in this case? ____________________N
c. Calculate the Mechanical Advantage (MA)
28. Calculate the work done when the object is moved 14 meters up the ramp using a
force of 100 N.