Impulse and Momentum

Moving objects have kinetic energy, proportional to the mass and the square of the speed.  Momentum is another measure of the motion of objects and is the product of an object’s mass and its velocity.

The graph on the left demonstrates momentum at different velocities for a constant mass and the graph on the right shows momentum at different masses at constant velocity.

There is a direct, linear relationship between both mass and momentum and velocity and momentum.  This means that if you triple the velocity or the mass of an object, its momentum will also triple.

The symbol we use for momentum is a lower case p. There are several theories why such a letter was chosen. Whatever the reason,  the letter p is as good as any other. The equation for momentum is simply momentum equals mass times velocity, or p = mv.

Since mass is measured in kilograms and velocity is measured in meters per second, the units for momentum are kilogram meters per second. 

Notice that this is not the same as Joules, which were kilogram meters squared per second squared.

The symbol p may be used for momentum because it is the mirror image of the letter q. Some people use p to represent the momentum of one object and q to represent the momentum of the other object in a recoil situation.

A clever way to write Newton's third law of motion is like this (+p = -q), since action is equal and opposite reaction.

Impulse and Momentum

Now, you will learn about how momentum and impulse are defined in physics. Pay special attention to the definitions, formulas, and examples as you view the presentation. Click the player button to begin.

View a printable version of the interactivity.

 

Impulse and Momentum Practice

While walking home from school today, Bob accidentally dropped the index cards that he had ordered, listing a set of forces, times, masses and changes in velocity.  Can you help him rearrange the cards to produce a complete set of correct impulses and changes in momentum?

To solve the puzzle, each set of cards would have to have a force, time, mass and change in velocity and the produce of force times time must equal the mass times change in velocity. All cards below the puzzle must be used.

Here is a printable version of the board and notecards if you would like to print them out so you can cut apart the notecards and place them in their correct positions on the board. After solving the puzzle, check your answers.