Kinetic and Potential Energy Review

Kinetic and Potential Energy Review

Middle School

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Learning Objectives

Key Vocabulary

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Potential Energy

Stored energy ready to be used by an object based on its position or state.

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Kinetic Energy

The energy an object has due to its motion, including the movement of its molecules.

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Work

The transfer of energy that happens when a force makes an object move over a distance.

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Conservative Forces

Forces where the work done moving an object does not depend on the path taken.

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Non-Conservative Forces

Forces where the work done on an object depends on the total path the object takes.

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Two Main States of Energy

Potential Energy

• Potential energy is the stored energy an object has due to its position or state.

• This type of energy is ready to be used but is not currently in action.

• A drawn bow or a book on a high shelf are examples of potential energy.

Kinetic Energy

• Kinetic energy is the energy that an object possesses because it is in motion.

• Any object that is moving, from an arrow in flight to a rolling ball, has it.

• The faster an object moves, the more kinetic energy it has.

Multiple Choice

A rollercoaster car is paused at the very top of a tall hill. What form of energy is most prominent at this moment?

• It has no energy

• Kinetic Energy

• Potential Energy

• Both are equal

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The Formulas for Energy

Gravitational Potential Energy

Kinetic Energy

Multiple Choice

According to the kinetic energy formula $$KE = \frac{1}{2}mv^2$$ , if two objects have the same mass but one has three times the velocity, how much more kinetic energy does the faster object have?

• Six times more

• Nine times more

• Three times more

• The same amount

Conservation of Energy

Multiple Choice

Based on the law of conservation of energy, what happens to the total energy of a swinging pendulum in a closed system?

• It increases as potential energy is converted to kinetic energy.

• It slowly disappears as the pendulum swings.

• It remains constant as energy transforms between potential and kinetic forms.

• It is greatest at the bottom of the swing.

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Work and Energy Transfer

Conservative Forces

• The work they do depends only on an object's starting and ending positions, not the path taken.

• Gravity is an excellent example of a conservative force that acts on all objects with mass.

• A ball rolling down a ramp or falling straight down has the same work done by gravity.

Non-conservative Forces

• The work done by these forces depends on the total distance an object travels along a path.

• Friction is a common non-conservative force that opposes the motion between two surfaces in contact.

• They often convert mechanical energy into other forms of energy, such as heat and sound.

Multiple Choice

Which of these scenarios describes a non-conservative force doing work?

• Lifting a weight straight up from the ground.

• An apple hanging from a tree branch.

• A book falling straight down from a shelf due to gravity.

• A box being pushed across a rough floor, generating heat from friction.

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Common Misconceptions About Energy and Work

Misconception	Correction
Energy can be 'lost' or used up.	Energy is transformed into other forms, like heat or sound.
An object at rest has no energy.	Objects at rest can have potential energy due to their position.
Applying a force always does work.	Work is done only when a force causes an object to move.

Multiple Choice

A 2 kg ball and a 4 kg ball are at the top of the same hill. How does the gravitational potential energy of the 4 kg ball compare to the 2 kg ball?

• It is four times the amount.

• It is double the amount.

• It is half the amount.

• It is the same.

Multiple Choice

How does the law of conservation of energy explain a bouncing ball eventually coming to a stop?

• On each bounce, some kinetic energy is transformed into sound and heat, reducing the total mechanical energy.

• Gravity eventually becomes stronger than the ball's energy.

• The ball runs out of energy and destroys it.

• The potential energy is completely lost on the first bounce.

Multiple Choice

A child slides down two slides of the same height. Slide A is short and steep, while Slide B is long and winding. Why might the child have a faster speed at the bottom of Slide A?

• The child has less mass on Slide A.

• Slide A has more potential energy.

• Less total work is done by friction on the shorter path of Slide A.

• Gravity is stronger on Slide A.

Multiple Choice

Using the principle of energy conservation $$E_i = E_f$$ , if a 1 kg object falls from a height of 20 meters $$g=9.8m/s^2$$ , what can you predict about its energy just before it hits the ground (ignoring air resistance)?

• The object's initial potential energy (196 J) will have been converted almost entirely into kinetic energy.

• The object's total energy will have doubled.

• The object will have lost all its energy.

• The object will have 0 kinetic energy.

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Summary

Poll

On a scale of 1-4, how confident are you about the concepts of kinetic and potential energy?

• 1

• 2

• 3

• 4