Collisions, Energy and Speed Elevate: Lesson

Energy , Speed and Collisions

What have you learned about Energy and Speed?

• Energy can be transferred

• Energy is conserved

• What happens during a collision?

• During a collision energy can produce sound, light and heat

COLLISIONS AND SOUND, LIGHT, AND HEAT

Energy Produces Sound

Some of the energy transferred during a collision produces sound. For example, the ball and the bat both have energy of motion because they are both moving. Energy transfers between the ball and the bat when they collide, so the ball's motion changes direction.

COLLISIONS AND SOUND, LIGHT, AND HEAT

Energy Produces Light

Sometimes light is produced when objects collide. This light transfers some energy away from the objects. For example, people can start fires by hitting a kind of rock called flint against a piece of steel.

COLLISIONS AND SOUND, LIGHT, AND HEAT

Energy Produces Heat

When objects collide, some of the energy is transferred and produces heat. Energy moves between any moving object and the surface it touches. When the energy moves, it creates heat and makes both objects warmer. That is why quickly rubbing your hands together warms them. Some of the energy of motion is changed into heat.

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Collisions

A collision is any crash or interaction between two or more objects.

What is a collision?

No!
There are two main types of collisions:
Elastic & Inelastic

Are all collisions the same?

These are crashes where the two objects get stuck together.

Since they're stuck together, they move as one, massive object; sharing one change in momentum.

​​Inelastic

These are crashes where the two objects hit each other then separate.

Since they separate, each object experiences their own changes in momentum after the crash.

Elastic

Both cars share a new momentum with their total mass:
p = (m₁ + m₂) * v

Their masses combine.

After Crash

Each object has its own starting momentum. p₁ & p₂

The total momentum before the crash: p₁ + p₂

Before Crash

Inelastic Collisions

Each car has its own final momentum: p_1f & p_2f

The total momentum after the crash: p_1f + p_2f

After Crash

Each object has its own initial momentum. p_1i & p_2i

The total momentum before the crash: p_1i + p_2i

Before Crash

Elastic Collisions

The Law of Conservation of Momentum

"For a closed system,
The total momentum before an event
is equal to the total momentum
after an event"

Lesson 10: Newton's Third Law

Action/Reaction​

​For every action, there is an equal and opposite reaction. This is Newton's Third Law of Motion. What that means is if you push on a wall, then the wall pushes back against you with an equal amount of force. When you hit a baseball with a bat, the ball pushes back against the bat with the same amount of force.

​Force Pairs

​A force pair is the forces two objects apply to each other. Force pairs are equal and opposite, but they do not cancel each other out (causing a net force of zero) because the forces act on different objects. Think of the baseball and the bat. They hit each other with the same amount of force, but the two forces act on different objects.

​Action/Reaction Forces

​When you push on an object, the object pushes back with an equal amount of force. The force you apply is called the action force. The force applied by the object in response is called the reaction force. Newton's Third Law explains how we can swim We push against water (action) and are propelled forward by the water pushing back on us (reaction).

​Momentum

​Since action and reaction forces don't cancel each other out, they can cause motion in the objects involved. Momentum, a measure of how hard it is to stop an object, is a product of the velocity and mass of an object.

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​The equation for momentum is:

​p = m x v where p stands for momentum.

​Momentum

​If a small sedan and an 18-wheeler are moving with the same velocity, then will they have the same momentum? No. The 18-wheeler is harder to stop because it has more mass than the sedan. It has greater momentum.

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Newton's first two laws relate to momentum. The first law states that if there is no net force on an object, it will not change momentum. The second law says the force on an object is a product of its mass and acceleration. Since momentum is a product of an object's mass and velocity (a component of acceleration), the force on an object equals its change in momentum.

​Conservation of Momentum

​If two objects collide, then they transfer their momentum to each other. In the case of a cue ball hitting other pool balls, the cue ball transfers its momentum to the other balls, causing them to gain momentum and the cue ball to lose momentum.

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​According to the law of conservation of momentum, the total momentum in a group of objects stays the same unless they are acted upon by outside forces.

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​So, why do the balls stop moving? Because of friction, an outside force, which slows them to a stop.