Energy and Collisions

Energy and Collisions

Middle School

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Learning Objectives

• Define the concepts of potential energy and kinetic energy.

• Describe how kinetic energy is proportional to mass and the square of speed.

• Explain that potential energy is stored in a system of interacting objects.

• Describe how energy is transferred between objects or forms and is always conserved.

• Apply Newton's Third Law to explain the forces present in a collision.

Key Vocabulary

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Energy

Energy is the capacity to do work or cause a change in an object's state.

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Potential Energy

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

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Kinetic Energy

Kinetic energy is the form of energy that an object possesses due to its motion.

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Energy Transfer

Energy transfer is the movement of energy from one system or object to another one.

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Collision

A collision is an event where two or more moving bodies exert forces on each other.

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Friction

Friction is a force that resists the relative motion between two surfaces that are in contact.

Key Vocabulary

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Newton's First Law

An object at rest or in motion stays that way unless acted on by an external force.

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Newton's Second Law

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Newton's Third Law

For every action, there is always an equal and opposite reaction between interacting objects.

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System

A group of interacting, interrelated, or interdependent objects or parts that form a complex whole.

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Interaction

A kind of action that occurs as two or more objects have an effect upon one another.

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Force Pair

The pair of equal and opposite forces that act on two interacting objects in a system.

Potential vs. Kinetic Energy

• Potential energy is the stored energy of an object's position.

• Kinetic energy is the energy an object has due to its motion.

• As an object falls, potential energy converts into kinetic energy.

Multiple Choice

Which statement correctly defines potential and kinetic energy?

• Potential energy is stored energy based on an object's position, while kinetic energy is the energy of a moving object.

• Kinetic energy is stored energy based on an object's position, while potential energy is the energy of a moving object.

• Potential energy and kinetic energy are both forms of energy related to an object's motion.

• Potential energy and kinetic energy are both forms of stored energy related to an object's position.

Multiple Choice

What is the relationship between potential and kinetic energy as an object falls?

• The object's potential energy decreases while its kinetic energy increases.

• The object's kinetic energy is converted into potential energy.

• Both potential and kinetic energy increase as the object falls.

• The object gains new energy from the air as it falls.

Multiple Choice

A roller coaster car is pulled to the top of its first and highest hill. At which point does it have the most potential energy?

• At the top of the hill, because its position gives it the most stored energy.

• At the bottom of the hill, because it is moving the fastest.

• Halfway down the hill, because it has equal amounts of both energies.

• The potential energy is the same at all points on the hill.

Potential Energy in a System

• Potential energy is stored within a system of interacting objects.

• It changes as the position of objects in the system changes.

• This applies to gravitational and magnetic forces between objects.

Multiple Choice

Which statement best defines potential energy?

• Stored energy within a system of interacting objects.

• Energy that an object has because of its motion.

• Energy that is created when objects collide.

• Energy that is lost to the environment as heat.

Multiple Choice

Under what condition does the amount of potential energy in a system change?

• When the objects in the system start to move faster.

• When the position of the objects in the system changes.

• When the temperature of the system increases.

• When the objects in the system are separated.

Multiple Choice

A magnet is stuck to a refrigerator door. If you pull the magnet away from the door, what happens to the potential energy of the magnet-refrigerator system?

• The potential energy increases because the magnet's position has changed relative to the refrigerator.

• The potential energy decreases because the magnet is no longer touching a surface.

• The potential energy stays the same because the magnet itself has not changed.

• The potential energy is converted to kinetic energy.

Energy Transfer and Conservation

• Energy is conserved; it only transfers or changes form.

• In collisions, kinetic energy transfers from one object to another.

• Friction can change an object's kinetic energy into thermal energy.

Multiple Choice

What does it mean for energy to be conserved?

• It is created during collisions and destroyed by friction.

• It only transfers between objects or changes into different forms.

• It can be lost completely when an object stops moving.

• It is a property that can only be found in hot objects.

Multiple Choice

When a moving billiard ball hits a group of stationary balls, they scatter and move. What is the relationship between the collision and the motion of the balls?

• Kinetic energy is created by the sound of the collision.

• Kinetic energy is transferred from the moving ball to the stationary balls.

• The total energy of the system is lost after the collision.

• Thermal energy from the balls is converted into kinetic energy.

Multiple Choice

A person pushes a heavy box, and it slides across the floor before coming to a stop. Which statement best explains the energy changes that took place?

• The box's kinetic energy was destroyed as it slid across the floor.

• The box's kinetic energy was transferred from the push and then transformed into thermal energy by friction.

• The floor absorbed all the kinetic energy, leaving none for the box.

• The initial push did not give the box enough energy to move forever.

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Kinetic Energy, Mass, and Speed

Relationship with Mass

Relationship with Speed

Multiple Choice

Which two factors determine an object's kinetic energy?

• Mass and speed

• Speed and height

• Mass and direction

• Weight and volume

Multiple Choice

If two cars are traveling at the same speed, but one car has double the mass of the other, what is true about its kinetic energy?

• The kinetic energy is halved.

• The kinetic energy doubles.

• The kinetic energy quadruples.

• The kinetic energy does not change.

Multiple Choice

A truck doubles its speed. What is the resulting change in its kinetic energy?

• The kinetic energy doubles.

• The kinetic energy triples.

• The kinetic energy increases by four times.

• The kinetic energy is reduced by half.

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Stopping Distance and Collisions

• Stopping distance is related to kinetic energy; more energy requires more work to stop.

• ​Speed has the greatest effect on a vehicle's kinetic energy and stopping distance.

• Tripling a car's speed increases its required stopping distance by nine times (3²).

• A heavier mass or less friction on the road increases stopping distance.

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Multiple Choice

What is the relationship between a vehicle's kinetic energy and its stopping distance?

• The more kinetic energy a vehicle has, the longer its stopping distance.

• The more kinetic energy a vehicle has, the shorter its stopping distance.

• A vehicle's kinetic energy and stopping distance are not related.

• Only very heavy vehicles have a long stopping distance.

Multiple Choice

According to the principles of kinetic energy, which factor has the greatest effect on a vehicle's stopping distance?

• The vehicle's speed

• The vehicle's mass

• The amount of friction on the road

• The direction the vehicle is traveling

Multiple Choice

If a car triples its speed, what is the resulting impact on its required stopping distance?

• The stopping distance will triple.

• The stopping distance will double.

• The stopping distance will increase by nine times.

• The stopping distance will not change.

Newton's Three Laws of Motion

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Law of Inertia

• An object will stay at rest unless an external force is applied.

• An object in motion maintains a constant speed in a straight line.

• A soccer ball on the ground will not move until it is kicked.

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Force, Mass & Acceleration

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Action and Reaction

• For every single action, there is an equal and opposite reaction.

• When you push against a wall, the wall pushes back on you.

• The two forces are equal in size but opposite in their direction.

Multiple Choice

Which statement best describes Newton's First Law of Motion, the Law of Inertia?

• An object will stay at rest or in motion unless an external force is applied.

• An object's acceleration is determined by its mass and the force applied to it.

• For every action, there is an equal and opposite reaction.

• The force of an action is always greater than the force of its reaction.

Multiple Choice

What is the relationship between an object's mass and the force needed to accelerate it?

• A greater force is required to accelerate an object with a larger mass.

• An object with a larger mass will always move faster than an object with a smaller mass.

• The same amount of force will accelerate a heavy object and a light object equally.

• An object's mass has no effect on the force needed to accelerate it.

Multiple Choice

A person pushes against a solid brick wall, but the wall does not move. Which statement best explains the forces involved in this scenario?

• The push on the wall results in an equal and opposite push from the wall onto the person.

• The person's push is stronger than the wall's push, causing them to feel pressure.

• The wall does not push back, but the person's muscles get tired from pushing.

• The person has more inertia than the wall, which prevents the wall from moving.

Newton's Third Law in Collisions

• In a collision, forces between objects are equal and opposite.

• The truck's force on the car equals the car's force on the truck.

• The smaller car accelerates more, resulting in greater damage.

Multiple Choice

In a collision, how do the forces between the two objects compare?

• The truck exerts a greater force than the car

• The car exerts a greater force than the truck

• The forces are equal and opposite

• There are no forces

Multiple Choice

When a large truck and a small car collide, which statement correctly describes the forces between them?

• The force of the truck on the car is greater than the force of the car on the truck.

• The force of the car on the truck is greater than the force of the truck on the car.

• The force of the truck on the car is equal to the force of the car on the truck.

• There is no force between the car and the truck, only damage.

Multiple Choice

If the forces between a colliding truck and car are equal, why does the car experience more acceleration?

• The truck exerts a greater force on the car than the car exerts on the truck.

• The car is moving faster than the truck before the collision.

• The car has less mass, so the equal force causes a greater change in its motion.

• The materials the car is made from are weaker than the truck's.

Applying Newton's Laws: Basketball

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Dribbling

• A player applies a downward force to move the ball.

• The ball accelerates toward the ground depending on its mass and the force applied (Law 2).

• The ground applies an equal and opposite force, making it bounce (Law 3).

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Running

• A player’s foot pushes backward on the floor, the action force.

• The floor pushes forward on their foot with an equal force.

• This opposite reaction force is what moves the player forward (Law 3).

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Shooting

• When the player applies a force to the stationary basketball, it accelerates toward the hoop based on its mass and the force applied. (Law 2).

• All forces between the ball and the player, or the ball and the ground, occur in action-reaction pairs (Law 3).

Multiple Choice

When a basketball player pushes backward on the floor while running, what is the floor's reaction?

• The floor pushes forward on the player's foot with an equal and opposite force.

• The player's body remains stationary until the ball is shot.

• The basketball begins to accelerate toward the hoop.

• The player's mass decreases, making them lighter.

Multiple Choice

How does Newton's Third Law explain why a basketball bounces after a player dribbles it?

• The force from the ground pushing back up on the ball causes it to bounce.

• The player's downward force is the only force making the ball move.

• The ball's mass is what makes it bounce after hitting the ground.

• The ball accelerates toward the hoop because the ground pushes it.

Multiple Choice

A player shoots two identical basketballs one after the other. If the player applies more force to the second ball, what can be predicted about its motion?

• The ball shot with more force will accelerate faster.

• The ball shot with less force will have more mass.

• Both balls will travel at the exact same speed.

• The ball shot with more force will stop moving sooner.

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Common Misconceptions

Misconception	Correction
In a collision, the bigger object exerts more force.	In any collision, the forces are an equal and opposite pair.
Energy is used up or destroyed.	Energy is conserved; it only changes form or transfers to another object.
An object at rest has no energy.	An object at rest can have potential energy because of its position.
Doubling speed doubles collision energy.	Doubling speed quadruples kinetic energy (22 = 4).

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Summary

Poll

On a scale of 1-4, how confident are you about applying these energy and collision concepts?

• 1 (Not confident)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)