MomentumMomentum

Chapter 7Chapter 7

MomentumMomentum

Momentum –Momentum – the product of the mass and the product of the mass and the velocity of an object (the velocity of an object (inertia in motioninertia in motion))

momentum = mvmomentum = mv

Momentum is a vector quantity (it has Momentum is a vector quantity (it has magnitude and direction)magnitude and direction)

A moving object can have a large A moving object can have a large momentum if it has a large mass, a high momentum if it has a large mass, a high speed, or bothspeed, or both

Impulse Changes MomentumImpulse Changes Momentum

If the momentum of an object changes, either If the momentum of an object changes, either the mass or the velocity or both change (usually the mass or the velocity or both change (usually it is just the velocity)it is just the velocity)

Acceleration will usually occur, produced by a Acceleration will usually occur, produced by a forceforce

How long the force acts is also important, so How long the force acts is also important, so both force and time are importantboth force and time are important

Impulse Impulse –– product of force and time interval product of force and time interval during which the force actsduring which the force acts

Impulse = FImpulse = FΔΔtt

Ft = Ft = ΔΔ(mv)(mv)

Impulse Changes MomentumImpulse Changes Momentum

Impulse and MomentumImpulse and Momentum

BouncingBouncing

Impulses are greater when an object Impulses are greater when an object bouncesbounces

The impulse required to bring an object to The impulse required to bring an object to a stop and then “throw it back again” is a stop and then “throw it back again” is greater than the impulse required merely greater than the impulse required merely to bring the object to a stopto bring the object to a stop

ReboundRebound

Conservation of MomentumConservation of MomentumFrom Newton’s Second Law we know that From Newton’s Second Law we know that to accelerate an object, a net force must to accelerate an object, a net force must be appliedbe appliedIf you wish to change the momentum of an If you wish to change the momentum of an object, exert an impulse on itobject, exert an impulse on itIf no net force or net impulse acts on a If no net force or net impulse acts on a system, the momentum of that system system, the momentum of that system cannot changecannot changeLaw of Conservation of Momentum:Law of Conservation of Momentum:In the absence of an external force, the In the absence of an external force, the

momentum of a system remains momentum of a system remains unchangedunchanged

CollisionsCollisions

Whenever objects collide in the absence of external Whenever objects collide in the absence of external forces, the net momentum of both objects before forces, the net momentum of both objects before collision equals the net momentum of both objects collision equals the net momentum of both objects after collisionafter collision

Net momentum Net momentum before collision before collision = Net momentum = Net momentum after collisionafter collision

Elastic CollisionElastic Collision – a collision in which colliding – a collision in which colliding objects rebound without lasting deformation or heat objects rebound without lasting deformation or heat generationgeneration

Inelastic Collision Inelastic Collision – a collision in which the colliding – a collision in which the colliding objects become distorted and/or generate heatobjects become distorted and/or generate heat

Elastic CollisionsElastic Collisions

Inelastic CollisionsInelastic Collisions

Collisions ContinuedCollisions Continued

Perfectly elastic collisions are not common Perfectly elastic collisions are not common in the everyday world, there will almost in the everyday world, there will almost always be heat generation or deformationalways be heat generation or deformation

In the microscopic world, perfectly elastic In the microscopic world, perfectly elastic collisions are commonplace; electrically collisions are commonplace; electrically charged particles bounce off each othercharged particles bounce off each other

AssignmentAssignment

Read Chapter 7 (pg. 86-99)Read Chapter 7 (pg. 86-99)

Do #19-38 (pg. 101-102)Do #19-38 (pg. 101-102)

Appendix F #1-10 (pg. 669-670)Appendix F #1-10 (pg. 669-670)