Momentum and Impulse

In Motion

Momentum

Any object that is moving has momentum even in the absence of gravity; therefore the egg had momentum, as did some of the athletes in the video.

Momentum is a term used to describe a quantity of motion.

In order to bring a moving object to rest such as the egg or an athlete, you must change the momentum to zero.

Momentum of an object is directly proportional to both its mass and velocity.

Simply stated, if a moving object has more mass, it has more momentum, and if an object has more velocity, it has more momentum.

For example the hockey or football player who speeds up or has a large mass, will be more difficult to stop/bring to rest than a player with a smaller mass or velocity.

Changing MomentumHow to stop a train . . . .

If we want to change an object’s momentum we need to apply a force to the object.

(* Remember Newton’s 1st Law, objects in motion want to stay in motion unless we apply an unbalanced force)

In order to determine the change in momentum we must also know how much time to apply the force for.

Impulse

The amount of force and the time during which the force is applied is called the IMPULSE.

More force equals more impulse, or if force is applied for a longer time it equals more impulse.

Impulse is proportional to force and time

Impulse – Momentum Relationship

In our egg example – in order to stop the egg, its momentum must be brought to zero. The only way to do this is to apply an impulse opposite to the eggs motion.

With the wall, the impulse is exerted over a very short period of time resulting in a large destructive force acting on the egg causing it to break.

When throwing the egg into the sheet the impulse is applied over a longer period of time consequently decreasing the applied force,

The sheet acted as a cushion, which is why the egg did not break.

If the force acts opposite to the objects motion the object slows down,.

If the force acts in the same direction as the object’s motion, the object will speed up.

This means that when velocity is changed, momentum is also changed.

Impulse changes momentum, which is why we call it an impulse – momentum relationship

Scenario 1: Cars ( not the movie )

Using the concepts of momentum and impulse in physics and using what we have discussed in the egg example: Describe some features of a car that will

help decrease incidence of injury in collisions. Also explain how they work using the terms momentum, impulse, velocity, mass, time and force.

Scenario 2: The Playground

If your group was in charge of designing the surface of a new child’s playground what kind of material would you use and why? Explain your answer by using physics

terms we talked about such as momentum, impulse, velocity, mass, time and force.

Scenario 3: A water balloon contest

If your group was in a water balloon throwing competition where you had to throw full water balloons between your group members at increasing distances while trying not to break them how would you use physics to help you win? Explain your answer by using terms we

talked about in class such as momentum, impulse, velocity, mass, time and force.

Scenario 4: Golfing

A professional golfer is trying to improve his performance. Using the physics concepts of momentum and impulse and terms we discussed in class such as velocity, mass, time and force, explain how the golfer could improve both his drive and putting skills.

Scenario 5: Hockey Hits

Using physics and the concept of momentum and impulse as well as some of the terms we discussed in class such as velocity, mass, time and force explain how you could use this to teach a hockey player how to “take a hit” properly to help reduce incidence of injury or possibilities of falling over

Relating Momentum and Impulse Mathmatically

Using a formula we can calculate the amount of momentum an object has.

Momentum = Mass x Velocity (the abbreviation for momentum is

p)

p = m * v

p = momentum m= mass v = velocity

Example 1

Calculate the amount of momentum that a 55kg hockey player has if he is skating at a velocity of 12 m/s.

p = 55kg * 12 m/s p = 660 kg/m/s

Calculating Change in MomentumΔp

Imagine a 25kg object moving at a velocity of 10m/s. It would have a momentum of

p ₁= m*v p₁ = 25kg * 10m/s = 250kg/m/s

Assume I applied some force to the object and slowed it down to a velocity of 5m/s

p₂ = m*vp₂ = 25kg * 5m/s = 125kg/m/s

Δp (the change in momentum) would be p₂ - p₁

Δp = p₂ - p₁ Δp = 125kg/m/s – 250kg/m/s

Δp = -125kg/m/s

We can also write this as

Δp = m₂v₂ - m₁v₁

Impulse

We can also calculate the impulse acting on an object.

Impulse = Force x Time

I = F * t

I = impulse F = force t = time

Example 2

What is the impulse on acting on a ball if a 150 N force is applied for 2 s?

I = 150N * 2sI = 300N/s

Impulse = Change in Momentum

Mathematically we can say that the impulse an object experiences is equal to the change in the objects momentum.

Impulse = Δ Momentum OR

F * t = Δp F*t = m₂v₂ - m₁v₁