Page 1 of 7. Momentum. Note: +/â Direction. matters for Force and. for Momentum. Momentum doesn't really have a great
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
Impulse
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.
