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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.

Sports are full of collisions. People walk, run, hit, kick, and back into each other, or pieces of equipment. As a result of these bumps the direction of one or more bodies is changed. Physics use the concept "momentum" is used describe these interactions. Every time one of these collisions happens momentum is shared between the bodies. You probably already have a feel for what momentum is. It is sometimes described as inertia for moving bodies. Momentum is a vector because it has direction and magnitude.

Momentum is modeled by the formula

Notice the unit for momentum is the product of the units of mass times velocity, kilogram meter per second.

Momentum's Signs

Momentum is a vector. This means it has direction and magnitude. Momentum's magnitude is calculated by the formula p=mv. The direction is in the same direction as the motion. when comparing the momentum's directions for two or more objects, mathematically, the signs are indicating the directions. The"+" indicates any direction. The "-" sign indicated the opposite direction of what was assumed to be the positive direction.

For the purpose of comparing results in the classroom, we will assume math conventions. Every object moving to the right or up is considered to have a positive direction. Every object moving in the opposite direction will have a negative sign. (Remember, this convention is just to make our lives easier when comparing results within our classroom. positive can be in any direction you choose -just be consistent in it application.)

Section Quiz


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