CH 5- MOMENTUM

B I G I D E A : T H E F O RC E A C T I N G O N A N O B J E C T M U LT I P L I E D BY T H E T I M E T H AT F O RC E A C T S E Q U A L S T H E O B J E C T S C H A N G E I N M O M E N T U M

5.1 MOMENTUM IS INERTIA IN MOTIONMomentum= 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 COLLISIONSIn any collision we can say:

Net momentumbefore collision = net momentumafter

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.