Momentum Momentum doesn't really have a great conceptual  definition.  It's best defined with an easy mathematical  definition (or "formula"), shown below...

* Notice the vector hats.  They mean that the direction of  momentum matters.

Note: +/‐ Direction  matters for Force and  for Momentum 


Momentum starts being useful if we start thinking  about how changes in motion can be related to  momentum ideas.  Check out the derivation below  of a new quantity called Impulse...

Note: +/‐ Direction  matters for Force and  for Momentum 

Conceptual  Example #1 How does the Impulse‐Momentum  Theorem help to explain the importance of  a baseball‐player "following through" with  his swing if he's trying to hit a homerun?  

The batter wants to cause the largest momentum‐change  possible, which means he needs to exert a large impulse on  the ball.  So he needs to swing hard to exert a large force,  but HE ALSO NEEDS TO FOLLOW THROUGH TO INCREASE  THE CONTACT TIME AS MUCH AS POSSIBLE.

Conceptual  Example #2

How does the Impulse‐Momentum  Theorem  help to explain how an airbag  makes the  stopping process safer during a car accident?  

The crash‐test dummy is going to undergo the same change in  momentum, regardless of the method of stopping, because its  momentum has to change from some original value to zero.  The  air bag INCREASES the TIME during which the stopping occurs,  compared to stopping by hitting the windshield.  This thereby  DECREASES the FORCE exerted on the dummy.

A 2kg object is initially moving at 5m/s in the positive  Ex. 17 direction, and 3 seconds later it is moving at 7m/s in the  negative direction.   a. Calculate the initial momentum of the object.

b.  Calculate the change in momentum of the object.

* Notice that  DIRECTION MATTERS! c.  Calculate the average force that acted on the object during the 3s interval.  

Ex. 18

A 23 kg block is sliding across a frictionless floor at 4 m/s,  when a 50 N force begins acting on it in the opposite  direction of its motion.  If the force acts for 2 seconds,  determine the magnitude and direction of the block’s  velocity after the force is done acting on it. 

Ex. 19

The only force acting on a 3kg object varies over time as  shown in the given graph.  Determine the speed of the  object at the  end of 10s, assuming the object started from  rest at t=0s.  

AP1 U2 Momentum & Impulse Notes.pdf

Page 1 of 7. Momentum. Note: +/‐ Direction. matters for Force and. for Momentum. Momentum doesn't really have a great conceptual. definition. It's best defined with an easy mathematical. definition (or "formula"), shown below... * Notice the vector hats. They mean that the direction of. momentum matters. Page 1 of 7 ...

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