Momentum
Momentum What do you think of when you hear the word “momentum”? ? ? ? ? ? ?
Momentum All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. The amount of momentum which an object has is dependent upon two variables: how much matter is moving? how fast the matter is moving?
Momentum: "mass in motion” Equation: p = m x v Unit: kg*m/s
Momentum Momentum is a vector quantity.
Momentum Consider a Mack truck and a roller skate moving down the street at the same speed. The considerably greater mass of the Mack truck gives it a considerably greater momentum. If the Mack truck were at rest, which would have the greater momentum? If an object is at rest, the momentum of that object is “0” because there is no mass in motion.
Momentum Questions 1. Determine the momentum of a ... a.) 60 kg halfback moving eastward at 9 m/s. b.) 1000 kg car moving northward at 20 m/s. c.) 40 kg man moving southward at 2 m/s. p = 540 kg*m/s, east p = 20,000 kg*m/s, north p = 80 kg*m/s, south
Momentum Questions 2. A car possesses 20,000 units of momentum. What would be the car's new momentum if ... a.) its velocity were doubled b.) its mass were doubled c.) both its velocity and mass were doubled p = 40,000 units p = 40,000 units p = 80,000 units
If the boulder and the boy have the same momentum, will the boulder crush the boy? Hint: think about the momentum formula! p = mv
Momentum and Impulse
Impulse/ DMomentum Theorem As the force acts upon the object for a given amount of time, the object's velocity is changed. Remember Newton’s 2nd law equation: F = ma & a = Dv/ Dt F Dt = D(mv) = mvf – mvi = m(vf – vi) Impulse = change in momentum
DEMONSTRATIONS Egg and the Blanket Bowling Ball
IMPULSE – A force applied for a period of time which results in a change of momentum. Impulse = change in momentum F∆t = ∆p = ∆(mv) F∆t = mvf - mvi F∆t = m (vf – vi)
To change the momentum of a body, a force must be applied to the mass To change the momentum of a body, a force must be applied to the mass. The longer this force is applied to the mass, the greater effect it will have on changing the momentum. F∆t = ∆(mv)
The Wall The Haystack
Impulse A change in momentum in a short time requires a large force. A change in momentum in a long time requires a small force.
Pop Quiz Hot Shot! What is the difference between impact and impulse? What happens to the force when the impulse remains the same and the time of impact increases by a factor of three? If force is kept constant, what happens to the change in momentum if time is cut in half? If force is kept constant, what happens to the impulse if time is doubled?
Miles Tugo and Ben Travlun are riding in a bus at highway speed on a nice summer day when an unlucky bug splatters onto the windshield. Miles and Ben begin discussing the physics of the situation. Miles suggests that the momentum change of the bug is much greater than that of the bus. After all, argues Miles, there was no noticeable change in the speed of the bus compared to the obvious change in the speed of the bug. Ben disagrees entirely, arguing that that both bug and bus encounter the same force, momentum change, and impulse. Who do you agree with? Support your answer.
Greatest velocity change? Greatest acceleration? Greatest momentum change? Greatest Impulse?
Therefore, a larger Force and impulse occurs!
Before the space shuttle lands, why does it take giant S curves? To increase landing time and decrease the force of the landing
Impulse Example: 1. An 80 kg skier loses control and demolishes a snow bank. If it takes the skier 3 seconds to come to rest from an impact speed of 9 m/s, find: (a) the impulse on the man (b) the average force exerted on him by the snow bank -720 kg*m/s -240 N
Lab Activity Materials Plot and calculate Impulse dynamic cart force sensor motion sensor Plot and calculate Impulse Plot Fvs t graph plot v vs t graph Area is equal to impulse change in momentum is equal to impulse
F vs t graph Area under the curve Constant F Find Area: =L x W = F x t 7500 F (N) 10 20 t (s)
Impulse from an F vs t graph Area under the curve Impulse = ∆F * t Find Area: = 2(1/2 *b*h) = 2(1/2*10*7500) = 75,000 Ns 7500 F (N) 10 20 t (s)