CH 5- MOMENTUM BIG IDEA: THE FORCE ACTING ON AN OBJECT MULTIPLIED BY THE TIME THAT FORCE ACTS EQUALS THE OBJECTS CHANGE IN MOMENTUM

5.1 MOMENTUM IS INERTIA IN MOTION Momentum= mass X velocity (momentum = mv) The more momentum something has, the more difficult it is to stop and the larger effect it will have in a collision

5.2 IMPULSE CHANGES MOMENTUM Force and the amount of time a force is being exerted produce acceleration If you exert the same force over a longer period of time, a greater change in momentum results Impulse- the quantity force times the time interval Impulse-momentum relationship: The greater the impulse exerted on something, the greater the change in momentum. Impulse= change in momentum OR Ft= change in mv

5.3 INCREASING MOMENTUM- INCREASE FORCE, TIME, OR BOTH Greatest momentum= greatest force over longest period of time

5.4 PRACTICAL USES OF THE IMPULSE- MOMENTUM RELATIONSHIP If you are in a fast moving vehicle and the brakes fail would you rather be forced to a stop by a wall or by a haystack? The haystack has a softer impact -Either way the momentum decreases by the same amount in coming to rest. By hitting the haystack instead of the wall, you extend the contact time- the time during which momentum is brought to zero.

THE IMPULSE-MOMENTUM RELATIONSHIP IN SPORTS Think about: Force-time-momentum relationship for: Boxers punching, tennis players hitting, Cushioned tennis shows/ mats, etc.

5.5 MOMENTUM IS CONSERVED WHEN NO EXTERNAL FORCE ACTS Internal forces don’t affect momentum To change momentum and outside force is required Law of conservation of momentum: In the absence of an external force, the momentum of a system remains unchanged.

5.6 MOMENTUM IS CONSERVED IN COLLISIONS In any collision we can say: Net momentum before collision = net momentum after collision Elastic collision:when objects collide w/out being permanently deformed and w/out generating heat

Inelastic collision- whenever colliding objects become tangled or coupled together By looking at the figure below we can see that the v is 5m/s. Twice as much mass moves after the collision, with half as much velocity as before the collision.