unit 5 test review

1) Introduction

2) Kinetic and potential energy

CORE CONCEPT

What type of energy does a ball have just before rolling down a

ramp?

The ball has potential energy at the top of a ramp.

When you ride your bike, when does it have only potential

energy and when does it have only kinetic energy?

A bike at the top of a hill has potential energy. The bike just reaching

the bottom of the hill has kinetic energy.

3) Cars and mechanical energy

CORE CONCEPT

What is the difference between kinetic energy and potential

energy?

Potential energy is stored energy, whereas kinetic energy is the energy

the object has while moving.

Why doesn’t the mechanical energy of the car change as it moves

down the ramp?

The mechanical energy of the car does not change as it moves down

the ramp because mechanical energy is not gained or lost.

4) Energy changing

EXTEND

How does a marble that rolls from the top to the bottom of a

ramp demonstrate the law of conservation of energy?

As the marble rolls down the ramp its potential energy is converted

into kinetic energy so that the total mechanical energy of the marble

remains the same.

EXTEND AND REFLECT

What kind of energy does a stretched rubber band have: kinetic

energy or potential energy?

A stretched rubber band has potential energy. Potential energy is

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energy stored in an object because of its position or shape. Energy is

stored in the rubber band when its shape is changed as it is stretched.

5) The law of conservation of energy

EXTEND AND REFLECT

If the skater hadn't gotten off of his skateboard, what would

have kept him from going forever (assuming he didn't wipe out)?

A little bit of energy is lost through friction all the time, so, though you

couldn't see it, he had a little less potential energy at the top of the

pipe every time he got there, so less potential energy to make it up

the other side. The energy lost through friction is thermal energy.

What is conservation of energy?

The energy of an object is conserved (not lost). The types of energy in

a system may change, but the total amount of energy does not.

6) Gravity and energy

EXTEND AND REFLECT

What is the force of gravity on the divers?

The force of gravity on the divers, and everyone on Earth, is equal to

the acceleration of falling objects, which is 9.81 meters per second per

second. This means that one second after the diver leaves the

platform he will be going at a speed of 9.81 meters per second.

VOCABULARY

What is the definition of potential energy?

Potential energy is the energy that an object has because of the

position, shape, or condition of the object.

7) Classifying energy

VOCABULARY

What is the definition of kinetic energy?

Kinetic energy is the energy of an object that is due to the object's

motion.

EXTEND AND REFLECT

What is the difference between a stretched rubber band and a

bike at the top of the hill?

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The stretched rubber band and a bike at the top of the hill both have

potential energy. The rubber band has elastic potential energy, and

the bike has gravitational potential energy.

8) The truth about energy

EXTEND AND REFLECT

How could you increase the mechanical energy of the roller

coaster?

You could increase the mechanical energy of the roller coaster by

letting more people ride it, which would increase the mass.

VOCABULARY

What is the definition of mechanical energy?

Mechanical energy is the amount of work an object can do because of

the object's kinetic and potential energies.

9) Potential energy

VOCABULARY

What is the definition of energy?

Energy is the capacity to do work.

10) Describing energy changes

CORE CONCEPT

Where does the soccer ball have the most kinetic energy?

The soccer ball has the most kinetic energy at the bottom of the ramp.

What happens to the mechanical energy of the soccer ball as it

rolls down a ramp?

The mechanical energy doesn’t change.

»»»»»»

1) Introduction

2) Acceleration

ENGAGE

Can you say that a car is accelerating when it slows down?

An object accelerates if its speed, direction, or both, change. So you

could say that the car is accelerating when it slows down, but it would

be less confusing to say that it is experiencing negative acceleration,

or decelerating.

VOCABULARY

What is the definition of acceleration?

Acceleration is the rate at which velocity changes over time. An object

accelerates if its speed, direction, or both, change.

3) Change in velocity

CORE CONCEPT

Why does a car accelerate if you turn the steering wheel?

When the car turns, it is changing direction. An object accelerates if its

speed, direction, or both, change.

How are velocity and acceleration different?

Velocity is an object's speed in a given direction, whereas acceleration

is a change in an object’s velocity over time.

4) Types of acceleration

CORE CONCEPT

What unit is used to express acceleration?

Acceleration is measured in meters per second per second, or meters

per second squared

EXTEND AND REFLECT

What is the acceleration due to gravity?

Acceleration due to gravity is 9.81 meters per second per second.

5) Acceleration equation

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EXTEND AND REFLECT

Why does the acceleration of the train contain a direction?

Because acceleration is a measure of the change in velocity, and

velocity includes both speed and direction.

What is meant by terminal velocity?

Terminal velocity is when an object's speed is constant due to the

restraining force exerted by the medium through which it travels. For

example, a skydiver in a belly-to-earth position will stop accelerating

at about 195 kilometers per hour because of the drag of the wind.

6) Calculations

CORE CONCEPT

How can an object have zero acceleration?

When an object has no change in velocity, it has zero acceleration.

EXTEND

When can an object have a negative acceleration?

When the object is slowing down it can be said to have negative

acceleration.

7) Centripetal acceleration

VOCABULARY

What is centripetal acceleration?

Centripetal acceleration is an acceleration of an object in a circular

path.

EXTEND AND REFLECT

What is centrifugal force?

You experience centrifugal force when a car changes direction and you

feel that you are being pushed in the away from the turn, or at the

bottom of a roller coaster when you feel that you are being pushed

down into your seat. It is a good example of Newton's first law of

motion, or the law of inertia: that your body resists any change in its

state of motion.

8) Acceleration facts

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EXTEND AND REFLECT

Why is option two not true about acceleration?

An object must have a change in speed or direction to accelerate.

If there is negative acceleration, can you also have negative

speed?

Acceleration is the rate at which velocity changes over time. It is a

quantity that has both size and direction, such as 9.81 meters per

second per second. Speed is the distance traveled divided by the time

interval during which the motion occurred. It is expressed as a single

number, such as 9.81 meters per second. You can't have negative

speed any more than you can have negative weight or negative

height. You can lose weight, but nothing weighs less than zero.

9) Identify acceleration

EXTEND AND REFLECT

What's the difference, in acceleration, between a train that is

waiting in the station and one that it traveling at 100 kilometers

per hour?

Both trains have zero acceleration. The train in the station has zero

velocity, too. The other train has a velocity of 100 kilometers per hour.

10) Describe acceleration

EXTEND AND REFLECT

Cars are often compared by how fast they go from zero to sixty.

What is this standard measuring?

Zero to sixty means how much time it takes for a car to accelerate

from no velocity to a velocity of sixty miles per hour. Performance cars

accelerate for six seconds to achieve this speed, and some exotic cars

can do it in three or four seconds..

MISCONCEPTIONS

Driving experts advise people to accelerate when entering a

curve. What to you think about this?

You know that a car that is changing direction — going into a curve —

is already accelerating. But what happens if you increase velocity and

change direction at the same time? Driving experts say that increasing

velocity in a curve, up to a certain point, gives the car better traction:

it stays on the road better.

»»»»»»

1) Introduction

2) What is speed?

CORE CONCEPT

How do the starting positions of car A and car B affect the

distance each car travels?

If car B starts further behind car A, car B must travel more distance

than car A.

EXTEND AND REFLECT

If the cars had started at the same position, which car would

have won the race?

Car B would have won the race because it traveled faster than car A.

3) Defining motion

VOCABULARY

What is speed?

Speed is an object’s distance traveled divided by the time it took the

object to travel.

CORE CONCEPT

Why are reference points important?

Reference points are important because we need to indicate from

where we are measuring a moving object.

4) Speed and average speed

CORE CONCEPT

What is the difference between speed and average speed?

Speed is the ratio of distance per time at a specific point in motion,

whereas the average speed is the total distance traveled divided by

the total time to travel in a trip from one point to the next.

Speed is a ratio of what two measurements?

Speed is the ratio of distance and time.

EXTEND AND REFLECT

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How does the distance a car travels change as it slows down?

The car travels less and less distance in the same time as it slows

down.

5) Speed and velocity

VOCABULARY

What is velocity?

Velocity is speed with a specific direction.

CORE CONCEPT

How can two objects have the same speed but different

velocities?

If the objects are moving in different directions they can have different

velocities but the same speed.

6) Distance-time graph

CORE CONCEPT

What is on the horizontal and vertical axis of a speed graph?

Distance is the vertical axis and time is the horizontal axis on a speed

graph.

EXTEND AND REFLECT

How does the steepness of the line on a speed graph relate to

the object’s speed?

The more speed the object has the steeper the line on the speed

graph.

7) Find the average speed

CORE CONCEPT

How can you calculate average speed?

Divide the total distance by the total time in order to calculate average

speed.

8) Graph distance and time

EXTEND AND REFLECT

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Does the speed increase throughout the graph? Explain your

answer.

No, there are instances where the speed does not increase. This is at

the points on the graph when the line is horizontal.

What is the relationship between speed and the slopes of the

lines on the graph?

Greater speeds correspond to steeper slopes on the graph.

9) Predicting speed

EXTEND AND REFLECT

What do you know about rat B if rat A finishes the race first?

We don’t know a lot about rat B except that it did not have a speed

significantly greater than rat A.

»»»»»»

1) Introduction

2) Roller coaster and forces

ENGAGE

Have you ever been on a roller coaster? What was it like?

If you have been on a roller coaster you already know a lot about

forces. Talking about a roller coaster sounds more interesting than

talking about forces, but it's really the same thing. Forces are involved

in everything you do.

Think about the roller coaster example. Can you think of other

everyday examples when forces come into play?

Some forces you might think of include riding a bicycle, rollerblading,

climbing steps — even picking up a pencil.

3) What are forces?

ENGAGE

Can you think of an example of something you pushed or pulled

today? How did you exert a force?

If you opened a door, you applied a force. If you closed one, you still

applied a force to move an object.

4) Types of forces

EVALUATE

Give an example of how magnetism can move an object.

A small horseshoe-shaped magnet can attract, or pull, objects like

nails toward it. The needle of a compass will move to point towards

the North Pole.

If you push a toy car as hard as you can across a rug it

eventually comes to a stop. Why is that? What forces will make it

stop?

You move the car by applying a force to it — or pushing it. But another

force made it stop. That force is friction. The rug pushes on the car in

the direction opposite to the car's motion.

EXTEND AND REFLECT

How are contact and non-contact forces alike? How are they

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different?

Both are forces and can push or pull on objects. But for contact forces

to affect motion, the objects must touch. Non-contact forces can act

from much farther away. A non-contact force, gravity, holds the moon

in orbit around Earth.

CORE CONCEPTS

If you put a glass of water on a table, it doesn't move or sink into

the table. What balanced forces are acting on it?

The force of gravity is balanced by the normal force applied by the

table.

5) Newton’s laws

EVALUATE

If you double the amount of mass in a shopping cart by adding

food to it, what do you have to do to the force to maintain the

same acceleration as you had before?

You have to double the force to maintain the same acceleration. Use

the formula used for Newton's Second Law of Motion.

6) Balanced and unbalanced forces

SYNTHESIS

When you're on a huge water slide what forces are at work?

When is your net force greater than zero?

Sitting at the top of the slide, you won't move. Forces acting on you —

gravity and the normal force — are balanced. When you move forward,

gravity is greater than friction, so your net force is greater than zero

and you accelerate down the slide.

EVALUATE

What role does force play in the game of tug-of-war?

When you start playing, both sides tug and may move forward, then

back a few times. Eventually, one side wins and falls backward, while

the other side crosses the line. The people holding the rope exert a

force by pulling on it. Whenever one team moves in either direction,

the forces are unbalanced.

7) Predicting direction

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CORE CONCEPTS

Look at the picture again. Suppose the two men were pushing

with equal force in opposite directions. How would the

refrigerator move?

Actually, it wouldn't. The forces acting on the refrigerator would be

balanced. An object at rest won't move unless the forces acting on it

are unbalanced. So, this refrigerator would stay put.

8) Inertia

LEARNING ALERT

What forces are acting on a car that is on cruise control on a

straight highway?

The car is maintaining its speed and direction, so the forces must be

balanced.

If a car maintains the same speed, but changes direction, are

balanced forces acting on it?

Acceleration is a change in velocity, which can involve a change in

speed, in direction, or in both speed and direction. If the car changes

direction, it is accelerating, so there must be an unbalanced force

acting on it.

9) Net force

CORE CONCEPTS

Which of Newton's laws must be considered when comparing

forces, masses, and accelerations?

When comparing forces you should use the second law, which

describes the relationship between mass, acceleration, and force.

10) Match Newton's laws

EXTEND AND REFLECT

What is an example of each of Newton's three laws?

An example of law one is a plane flying level at a constant speed. An

example of law two is two different cars with the same engine that

have different accelerations because of their masses. An example of

law three is leaning against a wall and the wall pushing back with

normal force.

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SYNTHESIS

Picture a book sliding across a table. How would you label it with

arrows showing all the forces acting on it?

The drawing would have an arrow to indicate the force pushing the

book in the direction of motion, another to show friction acting

opposite the direction of motion, a third to show gravity acting down,

and a fourth to show the normal force of the table pushing up.

»»»»»»»

1. Introduction

2. Free fall

CORE CONCEPTS

Why is the term "weightless" an incorrect term to describe an astronaut or object in space?

The force of gravity is still working on the person or object. Therefore, the person or object still has weight.

EXTEND AND REFLECT

How can you experience free fall without going into space?

Astronauts train for space by flying in a plane that enters a deep dive from a high altitude. This gives them about 25 seconds of free fall.

3. Weightless?

CORE CONCEPTS

Which would hit the ground first, a hammer or a feather, if dropped from the same height at the same time?

Because the acceleration due to gravity is the same for all objects, regardless of their mass, they should hit the ground at the same time. But it takes longer for a feather to fall because of air resistance. In July 1971, David Scott, one of the two astronauts who landed on the moon during the Apollo 15 mission, did a live demonstration of this experiment. Because there is no air on the moon, the feather and the hammer hit the ground at the same time.

EXTEND AND REFLECT

If a satellite is in free fall above Earth, does that mean it will eventually hit the ground?

It might take a long time, but all artificial satellites orbiting Earth will eventually fall close enough to be pulled back to Earth. Most of them, fortunately, will burn in the atmosphere before reaching the ground.

4. Force and mass

VOCABULARY

Why does a planet stay in orbit?

The sun's gravitational pull is pulling the planet toward the sun. The planet's forward motion continues due to inertia. These two motions combine so the planet follows a curved path.

EXTEND AND REFLECT

Why can astronauts jump so high, and "hang" so long, on the moon?

The astronaut's mass is the same, but, because the moon is so much smaller than Earth, the force of gravity is much less, too. So an astronaut weighs less on the moon, and because the force of gravity is weaker, acceleration due to gravity — or the speed with which things fall — is slower too.

5. Gravity and orbits

EXTEND AND REFLECT

How long does one complete orbit of Earth around the sun take?

We call one full orbit around the sun a year, but this year consists of 365.24218967 days. Because it is not an exact number of days, every four years we have a leap year to add on additional day, February 29, to make up for the four quarter-days that were "lost." But if you multiply 0.24218967 times four, it means that every four years we only add 0.96875868 days to the year. To compensate, years that are evenly divisible by 100 are not leap years, unless they are also evenly divisible by 400.

Why are leap years necessary?

A system of leap years is necessary in order to keep the calendar year synchronized with the seasons. If every year was just 365 days, and we ignored the additional time (5 hours, 48 minutes, and 45 seconds), the seasons would come later every year.

6. Law of gravitation

EXTEND AND REFLECT

"Fg" in the equation that describes the law of gravitation means the force of gravity. Why did scientists decide to name the unit of force "newtons"?

The unit "newton" was named after Sir Isaac Newton, who first described universal gravitation and the three laws of motion in the book Philosophiæ Naturalis Principia Mathematica that he published in 1687.

VOCABULARY

What is the definition of force?

Force is a push or pull exerted on an object in order to change the motion of the object. Force has both size and direction.

7. Gravitational force, mass, and distance

EXTEND AND REFLECT

What is a black hole?

A black hole is a region of space with a compact mass that has so much gravitational force that nothing, including light, can escape. It is theorized that a black hole is formed when a star cannot maintain its temperature and collapses in on itself.

After doubling the distance between the two balls, the gravitational force is reduced to one fourth. How much would you have to increase the mass of the first ball in order to have the gravitational force it had before doubling the distance?

When you double the mass, you receive twice the force. Since the doubled distance has reduced the force to one quarter, in order to achieve the previous force, you would have to increase the mass by four times.

8. Neptune

VOCABULARY

What is meant by the term "free fall"?

Free fall happens when the only force acting on an object is the force of gravity and the object falls at a constant rate.

EXTEND AND REFLECT

Why is Uranus's orbit different than originally calculated?

The force of gravity between Neptune and Uranus pulls Uranus a bit toward Neptune in its orbit around the sun.

9. Orbits

EVALUATE

What would happen to an orbiting space shuttle if the gravitational force between Earth and the shuttle suddenly disappeared?

The shuttle would move away from Earth in a straight line.

10. Gravity, mass, and distance

EXTEND AND REFLECT

What would happen to the force of gravity between the two balls if the distance between them was tripled?

The force of gravity would be one-ninth its original value.

CORE CONCEPTS

What does the force of gravity between two objects depend on?

The force of gravity depends on the mass of the objects and the distance between them.