Momentum and ImpulsePhysics: In Motion

Momentum

https://www.youtube.com/watch?v=2UHS883_P60

MomentumNewton combined the ideas of an object’s mass with its velocity and calculated its motion.

He called this motion momentum.

Momentum is the quantity of motion an object has.

Momentum is a measurement of mass in motion: how much mass is in how much motion.

MomentumTo bring an object to a stop, we must decrease the object’s momentum to 0.

MomentumMomentum is calculated according the the equation…

P = m•vP = momentum (N•s or kg•m/s)

m = mass of the object (kg)

v = velocity (m/s)

∆P = m•∆v

What is the momentum of a 100 000 kg train moving at 5.0 m/s?

What is the momentum of a 100 kg train moving at 5.0 m/s?

How do their momentums compare?

Momentum Calculations

Momentum CalculationsWhat is the momentum of a 10 kg toy car moving at 5m/s?

What is the momentum of a 10 kg toy car moving at 10m/s?

How do their momentums compare?

Momentum CalculationsCalculate the momentum of cart 1 – 3.00 kg cart moving at 30 m/s North.

Calculate the momentum of cart 2 – 2.00 kg cart moving 45.0 m/s South.

Can you say their momentums are equal? Why or why not?

Momentum Calculations RecapIf velocity increases, the momentum will increase at the same rate.If velocity decreases, the momentum will decrease at the same rate.

If mass increases, the momentum will increase at the same rate. If mass decreases, the momentum will decrease at the same rate.

Heavier objects travelling at the same velocity will have more momentum.Faster moving objects with the same mass will have more momentum.

Conservation of MomentumBy measuring the momentum of colliding objects before and after a collision, Newton found.

The total momentum of any system is conserved.

P(total before collision) = P(total after collision)

m•v(total before collision) = m•v(total after collision)

Conservation of MomentumEx. If a school bus collides with a car, the total momentum before the collision is equal to the total momentum after the collision (as long as there is no net force acting on the system).

There are two types of ways the collision could happen...

When the school bus and the car collide they can become one attached wreck.

Momentum of bus (before) + Momemtum of Car (before) = Momentum of bus/car (after)

mbusvbus mcarvcar mbus/carvbus/car

There are two types of ways the collision could happen...

When the school bus and the car collide they can become two separate wrecks.

Momentum of bus + Momentum of Car = Momentum of bus + Momentum of car(before) (before) (after) (after)

mbus1vbus1 mcar1vcar1 mbus2vbus2 mcar2vcar2

Car Crasheshttps://www.youtube.com/watch?v=c0tlOPorrDw

Collisionshttps://phet.colorado.edu/sims/collision-lab/collision-lab_en.html

What do you Remember about Momentum?

Momentum is the quantity of motion an object has.

Momentum is calculated by the following equation:

P = m•v

Momentum Recap

Momentum RecapThe total momentum of any elastic collision is conserved.

Conservation of Momentumhttps://www.youtube.com/watch?v=4IYDb6K5UF8

Momentum CalculationsWhat is the final momentum, if a 4000 kg bus travelling at 80km/h crashes into a car with a mass of 1000 kg travelling at a speed of 60 km/h?

Skateboard Momentum ExamplesThrow a medicine ball while on a skateboard.

What happens?

What’s happening with momentum?

Conservation of Momentum Example https://youtu.be/j1ugU_NwVLE?t=187

What can we do to reduce an object’s momentum to zero?

We can apply an Impulse!Impulse is the force acting on an object and the time interval the force is exerted.

Impulse is a vector quantity.

Impulse CalculationsImpulse is calculated by the following equation

I = F • tI = Impulse (N•s)

F = force (N)

t = time (s)

ImpulseSince impulse depends on both force and time, there is more than one way to apply a large impulse on an object.

To increase the magnitude of an impulse...

1. You can increase the force applied2. You can increase the length of time the force is being applied

Impulse Examplehttps://www.youtube.com/watch?v=K0ra7479zBs

Impulse Example ContinuedThe bedsheet had some ‘give’ to it. Thus, increasing the contact time and

distance and reducing the overall average force exerted on the egg.

The force of the egg is spread over the entire bedsheet and not just one

specific point.

This is the same idea as airbags

Impulse in VolleyballHow can you improve your spike? Improve your impulse!

1. Go to the gym to build up strength - this increases your force2. Follow through your hit - this increases your contact time with the ball

Increase force + increase time = increase in impulse

Impulse CalculationsImpulse is also defined as the change in an object’s momentum.

Therefore, it can also be calculated according to any of the following equations.

I = F•tI = ∆P

I = m∆vI = m(v2 - v1)

Impulse Calculations - BeginnerA force of 13N is applied to an object for 35s. What is the impulse acting on the object?

Impulse Calculations - IntermediateAn object has a momentum of 1000 kg•m/s.

What is the impulse acting on the object in order for it to stop moving?

What force is needed to stop in 1 second?

In 2 seconds?

Impulse Calculations - AdvancedHow many seconds would a force of 9.00 N have to act on a 3.00 kg mass in order to change its velocity from 4 m/s to 8 m/s?

Impulse Calculations - AdvancedA 3.00 kg ball moving with an initial velocity of +4.00 m/s is acted upon by a constant force F, for a period of 5.00 seconds. After the interaction, the ball is moving with a velocity of – 6.00 m/s. Find F.

Momentum and Impulse RecapWhen an unbalanced force acts on an object it will accelerate

A.k.a. it will change velocity - either speed up or slow down

When an object’s velocity changes, so does its momentum.P = m•v

When something exerts a force on you, it exerts an impulse I = F•t

Impulse changes Momentum and is also defined as I = ∆P

Cushioning the BlowThe impulse - momentum relationship is important to understand safety in car crashes.

A 2000kg car driving at 50km/h has a lot of momentum.

To reduce that momentum to 0kg•km/h we must apply an impulse opposite the car’s motion.

To do this safely we want to apply an impulse by exerting a force on the wheels for a long period of time.

Cushioning the BlowIn a collision the impulse is applied in a short period of time that result in destructive forces to the occupants.

To increase the length of time of an impulse during a car crash cars are designed to have a “crumple zone.”

A crumple zone is a part of a car that is designed to compress during an accident to absorb the impulse and increase the amount of time of the impulse, thus decreasing the force in the impulse.

I.e. Crumple zones mean that the impulse is reduced before it is passed on to the occupants in the vehicle.

Car Crasheshttps://www.youtube.com/watch?v=r8E5dUnLmh4&t=61s

https://www.youtube.com/watch?v=kly5BM8G3iM

Crumple Zones

Egg Drop InstructionsFind a group of 2 or 3.

Create your own contraption to reduce the force of an impulse by increasing the time of that impulse.

- The egg will be inserted into the contraption at the end and must be able to be taken out after the drop to be inspected.

Answer the questions on the handout.

Prepare for the drop zone.