Momentum Momentum inertia in motion 10242021 Momentum 2

Momentum

Momentum = inertia in motion 10/24/2021 Momentum 2

• Moving object has large momentum if – Mass is large (ship moving at slow speed) or – Velocity is large (bullet moving at rapid speed) or – Mass and Velocity are large (massive truck rolling down a steep slope with no brakes) 10/24/2021 Momentum 3

What is the momentum of the truck if it is NOT moving? 10/24/2021 Momentum 4

Why are the engines of supertankers turned off when they are 25 km from port? 10/24/2021 Momentum 5

• Changes in momentum may occur: – a change in the mass of an object – a change in velocity, – or both. 10/24/2021 Momentum 6

• If momentum changes but mass doesn’t – velocity changes…. . AND – acceleration occurs. • What produces an acceleration? – FORCE bigger Force bigger Δ in velocity bigger Δ in momentum 10/24/2021 Momentum 7

Collisions • Elastic: – colliding objects rebound without deformation or generation of heat – Colliding objects BOUNCE OFF OF EACH OTHER! • Inelastic – Colliding objects become distorted, generate heat, and possibly STICK TOGETHER! 10/24/2021 Momentum 8

Elastic Collisions Moving ball (green) strikes ball at rest (yellow) Head-on collision: Green ball stops, yellow ball moves away Both balls bounce away Two balls moving in same direction collide Green moving faster than yellow Momentum transferred from green ball to yellow Now yellow ball moving faster 10/24/2021 Momentum 9

Inelastic Collisions Sticking together! 10/24/2021 Momentum 10

Inelastic Collisions Deformation……………. 10/24/2021 Momentum 11

• You are hovering (REST) next to the space shuttle in earth-orbit • Your buddy of equal mass (moving at 4 m/s) (with respect to the ship) bumps into you. • If she holds onto you, how fast do the two of you move after the collision? • 2 x mass in motion after collision ½ v • The 2 astronauts move together with a velocity of 2 m/s after the collision. 10/24/2021 Momentum 12

Conservation of Momentum momentum before collision = momentum after collision m 1 v 1 = m 2 v 2 10/24/2021 Momentum 13

Big fish………little fish…… 10/24/2021 Momentum 14

Big fish…. . little fish (part 2) 10/24/2021 Momentum 15

Before collision, momentum of the loaded cart is 150 kg*cm/s momentum of the dropped brick is 0 kg*cm/s; total system momentum is 150 kg*cm/s. After the collision, momentum of the loaded cart is 90. 0 kg*cm/s momentum of the dropped brick is 60. 0 kg*cm/s total system momentum is 150 kg*cm/s. The momentum lost by the loaded cart (60 kg*cm/s) is gained by the dropped brick. 10/24/2021 Momentum 16

Before collision, momentum of the cart is 60 kg*cm/s momentum of the dropped brick is 0 kg*cm/s total system momentum is 60 kg*cm/s. After the collision, momentum of the cart is 20. 0 kg*cm/s momentum of the dropped brick is 40. 0 kg*cm/s total system momentum is 60 kg*cm/s. The momentum lost by the loaded cart (40 kg*cm/s) is gained by the dropped brick. 10/24/2021 Momentum 17

Before the collision, momentum of the car is 20 000 kg*m/s momentum of the truck is 0 kg*m/s total system momentum is 20 000 kg*m/s. After the collision, momentum of the car is -10 000 kg*m/s momentum of the truck is +30 000 kg*m/s total system momentum is 20 000 kg*m/s. The momentum lost by the car (30 000 kg*m/s) is gained by the truck. 10/24/2021 Momentum 18

Before the collision, momentum of the truck is 60 000 kg*m/s momentum of the car is 0 kg*m/s total system momentum is 60 000 kg*m/s. After the collision, momentum of the truck is 30 000 kg*m/s momentum of the car is 30 000 kg*m/s total system momentum is 60 000 kg*m/s. The momentum lost by the truck (30 000 kg*m/s) is gained by the car. 10/24/2021 Momentum 19

Before the collision, momentum of the car is +20 000 kg*m/s momentum of the truck is -60 000 kg*m/s total system momentum is -40 000 kg*m/s. After the collision, momentum of the car is -10 000 kg*m/s momentum of the truck is -30 000 kg*m/s total system momentum is -40 000 kg*m/s. The momentum change of the car (-30 000 kg*m/s) is equal in magnitude and opposite in direction to the momentum change of the truck (30 000 kg*m/s). 10/24/2021 Momentum 20

Before the collision, momentum of the car is +20 000 kg*m/s momentum of the truck is -60 000 kg*m/s total system momentum is -40 000 kg*m/s. After the collision, momentum of the car is -40 000 kg*m/s momentum of the truck is 0 kg*m/s total system momentum is -40 000 kg*m/s. The momentum change of the car (-40 000 kg*m/s) is equal in magnitude and opposite in direction to the momentum change of the truck (40 000 kg*m/s). 10/24/2021 Momentum 21

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Sources • http: //www. physicsplace. com • http: //www. physicsclassroom. com/ 10/24/2021 Momentum 23