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This text is meant to accompany class discussions. It is not everything there is to know about energy. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)
Click here for questions that go along with this section on Impulse and momentum.
Impulse

The process of transferring momentum is called impulse.

When a force is applied for period of time an impulse is delivered. Looking at the derivation you can combine two of the expressions for impulse to get a familiar relationship.

Impulse comes from Newton's 3rd law of motion.

When solving word problems, remember that the impulse to start an object moving from rest is equal and opposite to the impulse needed to stop that same object. This is a helpful problem solving strategy.
 
Example 1
A car with a mass of exactly 1000 kg starts from rest and travels to 25 m/s in 10.0 seconds. After traveling some distance at a constant speed the car applies the brakes and slows down to a stop in 5.0 seconds. Use impulse to find out how much force was used to stop the car.

 

A car with a mass of exactly 1000 kg starts from rest and travels to 25 m/s in 10.0 seconds. After traveling some distance at a constant speed the car applies the brakes and slows down to a stop in 5.0 seconds. Use impulse to find out how much force was used to stop the car.

This video can be found on YouTube at https://youtu.be/2de10Yl-TOU

 
Example 2
A 55.0 kg skateboarder starts from rest and reaches a speed of 6.00 m/s. The skateboarder coasts for a while without changing his speed. He then drags a foot along the ground for 8.00 seconds to slow down to a rest. How much force did he exert to slow himself down?

This video can be found on YouTube at https://youtu.be/PLrn5E3U8Y8
 
Example 2
A 55.0 kg skateboarder starts from rest and reaches a speed of 2.00 m/s. He uses his foot to push himself forward by pushing his foot along the ground with a force 400.0N. How much time did the push with his foot take?

 

 

This video can be found on YouTube at https://youtu.be/g2ClAITb0gE

 

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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