Impulse and Momentum

Impulse and Momentum

​AP Physics 1: Unit 5 Lesson 1

Objectives:

• Predict the change in momentum from the average force exerted on an object and the time interval during which it acts.

• Develop an expression to solve for a final or initial velocity of an object undergoing a change in momentum.

• Analyze data, graphs, and visual representations of objects undergoing a change in momentum.

​Momentum

• ​Mass in Motion

• ​2 variables

  • ​how much stuff is moving and how fast the stuff is moving

​Equations

• ​Momentum

  • ​p=mv Mass x Velocity

  • ​objects tendency to remain in motion

Poll

Is momentum vector or scalar quantity?

• Vector

• Scalar

Multiple Choice

Determine the momentum of 1000-kg car moving northward at 20 m/s......... 

• 20000 N
• 20000 Joules
• 20000 Kg * m/s
• 20000 kg * m/s north

Poll

A red truck and a blue truck have the same mass.  The red truck is parked, and the blue truck is traveling along the highway at 60 mph. Do both trucks have momentum?

• Yes

• No

Fill in the Blanks

Determine the momentum of Determine the momentum of a 60-kg halfback moving eastward at 9 m/s.

​Laws of Conservation (isolated system)

• a principle that the momentum before a collision is equal to the momentum after the collision

• ​What goes in must come out

​Equations

• Impulse

  • ​change in momentum

  • ​p_f - p_i = Δp (change)

    • ​p_f is the final momentum

    • ​p_i is the initial momentum

    • ​J is given to represent a change in impulse

      • ​J=Δp

• ​ F=J/Δt

• ​Δp=m(v_f-v_i)

Multiple Choice

Click on Image to enlarge.

Which image has the greatest change in velocity?

• A

• B

Multiple Choice

Click on Image to enlarge.

Which image has the greatest change in momentum?

• A

• B

Multiple Choice

Click on Image to enlarge.

Which image is impulse the greatest?

• A

• B

​Velocity Time Graph

• ​Case A

  • ​initial velocity 5 m/s

  • ​final velocity -3m/s

• ​Case B

  • ​initial velocity 3 m/s

  • ​final velocity -1 m/s

Multiple Choice

Click to enlarge image.

Which case has the greatest momentum?

• A

• B

Multiple Choice

Click to enlarge image.

Which case has the greatest impulse?

• A

• B

F vs. t graphs

Because impulse is the product of the sum of the forces and time interval, impulse is the area under a F vs. t graph.

​Elastic Collision (rebound)

• ​collision involving a change in direction and speed of motion and kinetic energy is conserved

​Inelastic Collision

• ​A collision involving a change speed but not direction of motion

  • ​momentum is conserved but Kinetic energy is transferred

​How we define the system matters...

​Consider two carts (A and B), both with a mass of 1 kg. Cart A is moving to the right at 2 m/s and Cart B is stationary. They collide; Cart A comes to rest, and Cart B moves to the right at 2 m/s.

Multiple Choice

A mosquito and a truck have a head-on collision. Splat! Which has a larger change of momentum?

• the mosquito

• the truck

• they have the same change in momentum

• can't say without knowing their initial velocities

Having a hard time accepting the mosquito- truck answer? Let's analyze...

​Inertia Versus Momentum

• ​Inertia

  • ​the resistance of an object to move

• ​momentum

  • ​mass in motion