Momentum Chapter 7

Momentum Momentum – the product of the mass and the velocity of an object (inertia in motion) momentum = mv Momentum is a vector quantity (it has magnitude and direction) A moving object can have a large momentum if it has a large mass, a high speed, or both

Impulse Changes Momentum If the momentum of an object changes, either the mass or the velocity or both change (usually it is just the velocity) Acceleration will usually occur, produced by a force How long the force acts is also important, so both force and time are important Impulse Impulse – product of force and time interval during which the force acts Impulse Impulse = FΔt Ft = Δ(mv)

Impulse Changes Momentum

Impulse and Momentum

Bouncing Impulses are greater when an object bounces The impulse required to bring an object to a stop and then “throw it back again” is greater than the impulse required merely to bring the object to a stop

Rebound

Conservation of Momentum From Newton’s Second Law we know that to accelerate an object, a net force must be applied If you wish to change the momentum of an object, exert an impulse on it If no net force or net impulse acts on a system, the momentum of that system cannot change Law of Conservation of Momentum: In the absence of an external force, the momentum of a system remains unchanged

Collisions Whenever objects collide in the absence of external forces, the net momentum of both objects before collision equals the net momentum of both objects after collision Net momentum before collision = Net momentum after collision Elastic Collision Elastic Collision – a collision in which colliding objects rebound without lasting deformation or heat generation Elastic Collision Inelastic Collision Inelastic Collision – a collision in which the colliding objects become distorted and/or generate heat Inelastic Collision

Elastic Collisions

Inelastic Collisions

Collisions Continued Perfectly elastic collisions are not common in the everyday world, there will almost always be heat generation or deformation In the microscopic world, perfectly elastic collisions are commonplace; electrically charged particles bounce off each other

Assignment Read Chapter 7 (pg ) Do #19-38 (pg ) Appendix F #1-10 (pg )