Bell Ringer After reading the article Does slamming on the brakes save your brake pads? Do you believe this saves gas?

Thought Question Would you feel safer in a Smart Car or another small car?

Momentum and Impulse

Momentum Momentum: The motion of inertia Variable: p momentum = mass x velocity p = mv Units: kg. m/s

Momentum Objects which aren’t moving have no velocity, and therefore have no momentum

Bell Ringer What is the advantage in having a padded dashboard?

Bell Ringer Two objects collide. If one has a heavier mass, what can we say about the forces experienced relative to the smaller mass?

Impulse Impulse: The change in momentum of an object due to a force that is applied during a period of time Variable: J impulse = force x time J = Ft Units: N. s

Impact Impact- The time duration in which a change in momentum is occurring. Units- seconds

Impulse-Momentum Theorem Impulse is equal to a change in momentum J =  p OR Ft =  (mv)

Bell Ringer Using the impulse momentum theorem answer the following question If you apply a force but extend the time, what will happen to the object’s change in momentum>

Bell Ringer A racket ball and a ball of clay of the same mass are thrown at an open door. Which one will be more effective in closing the door?

Bouncing Impulses are greater when the object bounces It takes additional impulse to stop an object and send it back in the opposite direction than it does to simply stop the object This additional impulse is supplied by the surface on which the object bounces

Forces of Impact Forces of impact are reduced when time of impact increases

Forces of Impact Forces of impact are also reduced when: the velocity of impact is reduced the mass of the object is reduced

Impulse Demos

Thought Question You step off of a skateboard. What happens to you? What happens to the skateboard?

Conservation of Momentum Momentum is a vector quantity It has magnitude and direction Momentum vectors, like forces, can cancel each other out

Conservation of Momentum

Law of Conservation of Momentum In the absence of an external force, the momentum of a system does not change.

Collisions In any collision the net momentum before the collision equals the net momentum after the collision There are two main types of collisions: elastic and inelastic

Elastic Collisions When objects collide without being permanently deformed and without generating heat Perfectly elastic collisions almost never occur Heat is usually generated with collisions, so energy is transformed out of the system

Elastic Collisions

Inelastic Collisions When colliding objects stick together and travel off as one object For two objects in an inelastic collision: momentum 1 + momentum 2 = combined momentum 1&2 m 1 v 1 + m 2 v 2 = (m 1 + m 2 )v f

Inelastic Collisions

Bell Ringer 10/18 One pool ball traveling with a velocity of 5 m/s hits another ball of the same mass, which is stationary. The collision is head on, as momentum is conserved, and they bounce off each other. What type of collision is this? What are the final velocities of both bodies?

Thought Question When is momentum not conserved?

Rain vs. Hail Which has a greater change in momentum? Which has a greater impulse? Which causes more damage?

Topic Review 1.) Why are padded dashboards used in cars? 2.)

Bell Ringer 3/28 A kg baseball moving at a speed of 45.0 m/s crosses the plate and strikes the kg catcher's mitt (originally at rest). The catcher's mitt immediately recoils backwards (at the same speed as the ball) before the catcher applies an external force to stop its momentum. Determine the post-collision velocity of the mitt and ball.

Bad Momentum Videos

Bell Ringer Two meatballs are speeding directly toward each other. One is a 4.0-kg meatball moving with a speed of 6.0 m/s, and the other has a mass of 2.0 kg and a speed of 4 m/s. If they collide inelastically, what will be the speed of the resulting 6.0 kg meatball immediately after the collision?

Review Question A bullet with a mass of kg collides inelastically with a wooden block of mass 2.5 kg, initially at rest. After the collision, the bullet + block has a speed of 1.2 m/s. What was the initial speed of the bullet?