Forces Transfer Momentum (2.4)

·      The “Big Idea”:

-      Forces change the motion of objects in predictable ways.

·      Now you will learn:

-      What momentum is

-      How to calculate momentum

-      How momentum is affected by collisions




Objects in motion have momentum.

·      Momentum-   a measure of mass in motion; the momentum of an object is the product of its mass and its velocity.

-      At the same velocity, a bowling ball has more momentum than a tennis ball because it has more mass.

-      How could you increase the momentum of the tennis ball?


You could increase the momentum by throwing it faster.



·      How is momentum similar to inertia? How is it different?


Momentum is similar to inertia since it depends on mass.  It is different because it takes into account how fast an object is moving.


·      Would a slower moving wrecking ball do as much damage as a faster moving one?


No.  The faster an object is moving the more damage it would do.




·      Calculating momentum:

momentum= mass x velocity

p= mv

·      Units: kg m/s



1.   What is the momentum of a 2 kg ball moving at 2 m/s?

p= mv 

p= 2 kg x 2 m/s

p= 4 kg m/s


2.    What is the momentum of a 4 kg rock moving at 3 m/s?

p= mv 

p= 4 kg x 3 m/s

p= 12 kg m/s


Momentum can be transferred from one object to another.

·      Collision-  A situation in which two objects in close contact exchange energy and momentum.


-      In a collision, action/reaction forces transfer momentum.


-      Think of bumper cars:

1.  As another car bumps the back of yours, the force pushes your car forward.

2.  Momentum is transferred from that car to your car.

3.  The car behind you slows because of the reaction force of your car.

4.  You gain momentum from the collision.

** If colliding objects have very different masses, then the one with less mass has a greater change in velocity.


Momentum is conserved.

·    Conservation of momentum-  The total momentum of a system of objects does not change, as long as no outside forces are acting on them.