Kinetic energy

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Definition of Kinetic Energy

Kinetic energy is the energy an object or system has because it is moving.
It is often called the energy of motion.
A flying bee, a racing motorcycle, flowing water, and a spinning saw blade are all moving, so they all have kinetic energy — mass and material do not matter, only motion does.
A stop street sign, two chairs, and an apple (at rest) do not have kinetic energy because they are not moving.

A flying bee, a racing motorcycle, flowing water, and a spinning saw blade

Factors Affecting Kinetic Energy

An object's kinetic energy depends on two factors: mass and speed.
The greater the mass, the more kinetic energy the object has.
The greater the speed, the greater the kinetic energy.
Kinetic energy is proportional to mass and grows with the square of speed.
A car travelling at 200 km/h has more kinetic energy than at 100 km/h.

Mass and Kinetic Energy Investigation

Rolling balls of different masses down a ramp into a paper cup shows how mass affects kinetic energy.
In the experiment, a glass marble (20.4 g) moved the cup 208 cm, a plastic marble (9.5 g) moved it 107 cm, and a styrofoam ball (0.2 g) moved it 0 cm.
The pattern: as mass increases, the distance the cup moves increases, indicating more kinetic energy.
This evidence supports that moving objects with more mass have more kinetic energy.

Marble mass vs. distance moved

Speed and Kinetic Energy Investigation

Rolling a toy car at different speeds and measuring how far it travels shows how speed affects kinetic energy.
In the experiment, a slow car moved 250 cm, a medium car moved 882 cm, and a fast car moved 1450 cm.
The pattern: as speed increases, the distance the car travels increases, indicating more kinetic energy.
This evidence supports that objects with more speed have more kinetic energy.

Toy car speed vs. distance travelled

Kinetic vs. Potential Energy

Potential energy is stored energy, such as a ball at the top of a ladder or petrol in a tank.
Kinetic energy is the energy of motion, such as a moving car or flowing water.
Some systems have both types, like a high jumper at the peak of a jump (has potential energy and some kinetic energy).
A mountain biker at the top of a mountain has potential energy; a race-car at maximum speed has kinetic energy.
A spring in a pinball machine before release has potential energy; a running refrigerator motor has kinetic energy.

A high jumper going over the bar

Energy Transfers and Conservation

The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or transformed.
Energy transfers occur between systems, e.g., a kettle plugged in transfers electrical energy to thermal energy to heat water.
In a high jumper's jump, as she rises, kinetic energy is converted to potential energy; at the top, she has maximum potential energy and minimum kinetic energy.
When she falls, potential energy converts back to kinetic energy.

Real-World Applications

Wind is moving air particles, so they have kinetic energy.
Food contains stored potential energy that our bodies use for movement and functions.
A baseball has more kinetic energy than a wiffle ball when hit with the same force because it has more mass.
A full cart has more kinetic energy than an empty cart moving at the same speed due to greater mass.

A baseball bat about to hit a wiffle ball, and a baseball bat hitting a baseball

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1.What is kinetic energy?
Easy
- AEnergy stored in an object due to its position
- BEnergy that an object has because it is moving
- CEnergy stored in chemical bonds
- DEnergy transferred by heat
2.Kinetic energy is the energy of motion.
Easy
True or false?
3.Which of the following objects has kinetic energy?
Easy
- AA book resting on a shelf
- BA stretched rubber band
- CA bird in flight
- DA parked car
4.A car travelling at 200 km/h has more kinetic energy than a car travelling at 100 km/h.
Easy
True or false?
5.What are the two factors that affect the kinetic energy of an object?
Easy
- AMass and height
- BMass and speed
- CSpeed and temperature
- DWeight and volume
6.Arrange the following objects in increasing order of kinetic energy, assuming they are all moving at the same speed.
Easy
- A styrofoam ball (0.2 g)
- A plastic marble (9.5 g)
- A glass marble (20.4 g)
7.Match each object to the type of energy it primarily has.
Medium
- A moving car
- A stretched elastic band
- A ball at the top of a hill
- Kinetic energy
- Potential energy
- Potential energy
8.Match each object to whether it has kinetic energy (Yes) or not (No).
Easy
- A lady running
- A stop street sign
- A roller coaster
- Yes
- No

Thêm câu hỏi

9.Which of the following systems contain kinetic energy? (Select all that apply)
Medium
- AWater flowing down a waterfall
- BPetrol in a storage tank
- CA race-car travelling at maximum speed
- DA spring in a pinball machine before release
- EA running refrigerator motor
10.A bird in flight has kinetic energy.
Easy
True or false?
11.Kinetic energy is proportional to the square of the speed of an object.
Easy
True or false?
12.In the toy car experiment, when the car was going at slow speed it moved 250 cm, at medium speed 882 cm, and at fast speed 1450 cm. Which statement best explains the pattern?
Medium
- AAs speed increases, kinetic energy decreases.
- BAs speed increases, kinetic energy increases.
- CSpeed has no effect on kinetic energy.
- DThe car's mass changes with speed.
13.A baseball and a wiffle ball are hit with the same force. The baseball goes farther because it has a larger mass. What does this demonstrate about kinetic energy?
Medium
- AKinetic energy depends on speed only.
- BKinetic energy depends on mass only.
- CKinetic energy depends on both mass and speed.
- DKinetic energy is independent of mass and speed.
14.Which of the following statements about kinetic energy are true? (Select all that apply)
Medium
- AKinetic energy is the energy of motion.
- BKinetic energy is proportional to the mass of the object.
- CKinetic energy grows with the square of the speed.
- DKinetic energy is stored in stretched elastic bands.
- EA stationary object can have kinetic energy.
15.Match each situation to the type of energy it primarily has (kinetic, potential, or both).
Medium
- A mountain biker at the top of a mountain
- Water flowing down a waterfall before hitting the pond
- A spring in a pinball machine before it is released
- A race-car travelling at its maximum speed
- Potential
- Kinetic
- Potential
- Kinetic
16.A student rolls a heavy glass marble and a light styrofoam ball of the same size down a ramp into a paper cup. The glass marble moves the cup 208 cm, while the styrofoam ball does not move the cup at all (0 cm). What is the most likely reason for this difference?
Medium
- AThe styrofoam ball has no kinetic energy because it is too light.
- BThe glass marble has more kinetic energy because it has more mass.
- CThe styrofoam ball has more kinetic energy because it is lighter.
- DThe glass marble has less kinetic energy because it is heavier.
17.A race-car travelling at its maximum speed has kinetic energy.
Easy
True or false?
18.Two identical cars are moving on a highway. Car A is travelling at 50 km/h and Car B is travelling at 100 km/h. How does the kinetic energy of Car B compare to that of Car A?
Medium
- ACar B has twice the kinetic energy of Car A.
- BCar B has four times the kinetic energy of Car A.
- CCar B has half the kinetic energy of Car A.
- DCar B has the same kinetic energy as Car A.
19.In the marble experiment, which of the following variables should be kept constant to ensure a fair test? (Select all that apply)
Medium
- AThe mass of the marble
- BThe height of the ramp
- CThe type of surface the cup is on
- DThe distance the cup moves
- EThe size of the marble
20.In the toy car experiment, the car moved 250 cm at slow speed, 882 cm at medium speed, and 1450 cm at fast speed. This data supports the claim that kinetic energy is directly proportional to speed.
Medium
True or false?
21.In the toy car experiment, the car moved 250 cm at slow speed, 882 cm at medium speed, and 1450 cm at fast speed. If the speed of the car triples from slow to fast, what is the approximate ratio of the distances moved, and how does this compare to the expected ratio if kinetic energy is proportional to the square of the speed?
Hard
- AThe ratio is about 5.8, which is close to the expected ratio of 9, so it supports the square relationship.
- BThe ratio is about 5.8, which is far from the expected ratio of 9, so it disproves the square relationship.
- CThe ratio is about 3.5, which is close to the expected ratio of 3, so it supports direct proportionality.
- DThe ratio is about 5.8, and since it is not 9, the experiment is invalid.
22.A stop street sign has kinetic energy.
Easy
True or false?
23.A helicopter in flight has kinetic energy.
Easy
True or false?
24.An apple hanging on a tree has kinetic energy.
Easy
True or false?
25.Kinetic energy is proportional to the mass of the moving object.
Easy
True or false?
26.In the toy car experiment, the car moved 250 cm at slow speed, 882 cm at medium speed, and 1450 cm at fast speed. If the speed doubles from slow to medium, the distance the car moves increases by approximately a factor of:
Medium
- A2
- B3.5
- C4
- D5.8
27.Complete the sentence:
Easy
Kinetic energy is the energy that an object or system has because it is ____.
28.In an experiment, a styrofoam marble (mass 0.2 g) moved a paper cup 0 cm, a plastic marble (9.5 g) moved it 107 cm, and a glass marble (20.4 g) moved it 208 cm. What is the distance the cup moved for the glass marble?
Easy
29.What is the energy of motion called?
Easy
30.In the marble experiment, a glass marble (mass 20.4 g) moved a paper cup 208 cm. A plastic marble (mass 9.5 g) moved the cup 107 cm. Approximately how many times greater is the kinetic energy of the glass marble compared to the plastic marble? (Give your answer to one decimal place.)
Easy
31.In the marble experiment, what property of the marble is changed to investigate its effect on kinetic energy?
Easy
32.Complete the sentence using the correct terms.
Medium
Kinetic energy is proportional to the ____ of the moving object and grows with the ____ of its speed.
33.Complete the sentences below about energy changes for skydivers.
Easy
When a plane carries skydivers high into the sky, it is giving them ____ energy. When they jump out and free-fall, they have ____ energy.
34.In the toy car experiment, the car moved 250 cm at slow speed, 882 cm at medium speed, and 1450 cm at fast speed. Explain how this data supports the claim that kinetic energy increases with speed.
Medium
35.In the marble experiment, a glass marble (mass 20.4 g) moved the cup 208 cm, while a styrofoam marble (mass 0.2 g) moved it 0 cm. Explain why the glass marble caused the cup to move much farther.
Medium
36.In an experiment, a styrofoam marble (mass 0.2 g) moved a paper cup 0 cm, a plastic marble (9.5 g) moved it 107 cm, and a glass marble (20.4 g) moved it 208 cm. What is the distance the cup moved for the glass marble?
Easy
- A208 cm
- B187 cm
- C250 cm
- D229 cm
37.In the marble experiment, a glass marble (mass 20.4 g) moved a paper cup 208 cm. A plastic marble (mass 9.5 g) moved the cup 107 cm. Approximately how many times greater is the kinetic energy of the glass marble compared to the plastic marble? (Give your answer to one decimal place.)
Easy
- A1.9 times
- B2.9 times
- C0.9 times
- D3.9 times
38.A high jumper sprints towards the bar, jumps, rises into the air, and lands on a soft mat. At the highest point of her jump, just above the bar, her upward speed is momentarily close to zero. What does this tell you about her energy at that instant?
Medium
- AHer kinetic energy is at its maximum and her potential energy is at its minimum.
- BHer kinetic energy is close to its minimum and her potential energy is at its maximum for the jump.
- CBoth her kinetic energy and potential energy are zero at this point.
- DBoth her kinetic energy and potential energy are at their maximum at this point.
39.As a skater speeds up, what happens to her kinetic energy (assuming her mass stays the same)?
Easy
- AIt increases
- BIt decreases
- CIt stays the same
- DIt becomes zero
40.Students dropped a glass marble (mass 18.5 g) into a cup of flour from a height of 50 cm. Its speed on impact was 3.1 m/s and its kinetic energy on impact was 88.9 g·m²/s². They repeated the drop from the same height using a glass marble with double the mass (37.0 g), and it hit the flour at the same speed, 3.1 m/s. How does the second marble's kinetic energy compare to the first marble's?
Medium
- AIt is about half as much, around 44 g·m²/s²
- BIt is about the same, around 89 g·m²/s²
- CIt is about double, around 178 g·m²/s²
- DIt is about four times as much, around 356 g·m²/s²
41.A student starts at rest on a bicycle and then rides faster and faster. Which graph best shows the relationship between her speed and her kinetic energy as she speeds up?
Medium
- AGraph 1 — kinetic energy stays the same as speed increases
- BGraph 2 — kinetic energy decreases as speed increases
- CGraph 3 — kinetic energy increases faster and faster as speed increases
- DNone of the graphs — speed and kinetic energy are not related
42.The graph shows the kinetic energy of three skaters (40 kg, 60 kg, and 80 kg) at the same ten positions on a half-pipe ramp, so at any one position all three skaters are moving at the same speed. Describe how the mass of a skater affected her kinetic energy. Use a quantitative example from one ramp position to support your answer.
Medium

Ghi chú ôn tập

## Kinetic Energy - Key Points - **Kinetic energy** is the energy an object has due to its motion. - It depends on **mass** and **speed**: heavier or faster objects have more kinetic energy. - The formula is: **KE = ½ mv²** where m = mass (kg), v = speed (m/s), KE = energy in joules (J). - Kinetic energy increases with the **square of speed**: doubling speed quadruples KE. - It can be transferred between objects or transformed into other forms (e.g., heat, potential energy). - **Work** is done to change kinetic energy: work = force × distance (in direction of motion). - The same amount of work is needed to stop a moving object as was used to start it. - Examples: - A moving bicycle has kinetic energy; pedaling converts chemical energy to KE. - Coasting uphill converts KE to gravitational potential energy. - Brakes convert KE to heat via friction. - In everyday situations (speeds much less than light), the formula KE = ½mv² is accurate. ## Key Terms

Kinetic energy: The energy an object possesses due to its motion.
Joule: The SI unit of energy; one joule equals the work done by a force of one newton over a distance of one meter.
Mass: The amount of matter in an object, measured in kilograms (kg).
Speed: How fast an object is moving, measured in meters per second (m/s).
Work: The transfer of energy when a force moves an object over a distance; work = force × displacement in the direction of the force.
Potential energy: Stored energy that an object has due to its position or condition (e.g., gravitational potential energy).

Thẻ ghi nhớ

What is kinetic energy?

Kinetic energy is the energy an object has because of its motion.

What two factors does kinetic energy depend on?

Kinetic energy depends on the mass and speed of the object.

Write the formula for kinetic energy in classical mechanics.

KE = 1/2 mv², where m is mass and v is speed.

What is the SI unit of kinetic energy?

The joule (J).

What is the English unit of energy?

The foot-pound.

How does doubling the speed of an object affect its kinetic energy?

Doubling the speed quadruples the kinetic energy (since v is squared).

How does doubling the mass of an object affect its kinetic energy?

Doubling the mass doubles the kinetic energy (since mass is directly proportional).

What is the relationship between kinetic energy and work?

The kinetic energy of an object equals the work needed to accelerate it from rest to its speed.

What happens to kinetic energy when an object slows down?

The object does work equal to its kinetic energy to decelerate to rest.

Give an example of kinetic energy being transformed into another form.

A cyclist coasting up a hill converts kinetic energy into gravitational potential energy.

What does the Greek word 'kinesis' mean?

It means 'motion', and is the root of the word 'kinetic'.

Who coined the term 'kinetic energy'?

William Thomson (Lord Kelvin) around 1849–1851.

What experiment showed that penetration depth is proportional to the square of impact speed?

Willem 's Gravesande's experiment dropping weights into clay.

What is the approximation condition for the classical kinetic energy formula?

It is a good approximation only when speed is much less than the speed of light.

Can kinetic energy be negative?

No, because mass and the square of speed are always positive.

Does kinetic energy depend on the observer's frame of reference?

Yes, kinetic energy depends on the relative motion between the object and the observer.

What happens to kinetic energy in a perfectly circular orbit?

It remains constant because there is almost no friction in near-Earth space.

In an elliptical orbit, where is kinetic energy greatest?

At closest approach to the massive body (periapsis).

What is the sum of kinetic and potential energy in an isolated system?

The sum remains constant (conservation of mechanical energy).

Give an example of kinetic energy being converted to heat.

Applying brakes on a bicycle converts kinetic energy to heat via friction.

What form of energy does a cyclist use to increase kinetic energy?

Chemical energy from food.

What is the term for the energy of motion?

Kinetic energy.

What is the difference between kinetic and potential energy?

Kinetic energy is energy of motion; potential energy is stored energy due to position or configuration.

Can kinetic energy be transferred between objects?

Yes, for example in collisions.

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