Momentum

AP Physics – Momentum

Momentum is a common word – you hear it every so often, but not like every day, normally.   Sportscasters will say that a team has a “lot of momentum”.     Or a news anchor person might say “the need for federal regulation of the qualification of physics teachers is gaining momentum”.   A kind of related thing would be the idea that something is momentous (which would mean that it was important).

Momentum sounds important too.   If something has momentum, well, that’s got to be a big deal.   It has MOMENTUM!

Well, forget all that!   In physics momentum is simply the velocity of an object multiplied by its mass.

When something is at rest it has a certain quality which is very different from the one it has when it is moving.   You would feel safe stepping in front of a locomotive and pushing on its nose – if it were at rest.   But you would not want to do this if it was moving.   Especially if it was moving fast.   This is because of its momentum.

Momentum can be thought of as sort of like inertia in motion.   Recall that inertia is the property of matter that is responsible for Newton’s first law.   It resists changes in a system’s motion. Anyway, the thing with momentum is that when things are moving, the inertia seems to get amplified or something.     See, when something gets underway, the faster it goes the more it seems to want to keep moving.

Here’s an important thing about momentum:

                Momentum is a vector quantity.

Momentum in mathematical terms is:

[pic] Momentum Equation

                Where p is momentum, m is mass, and v is velocity.

Momentum has units of: [pic] or [pic]

To have momentum, an object must have a velocity - be moving.   A strand of spider web silk drifting on the air currents has more momentum than a mile long coal train that is waiting on a siding.

• What is the momentum possessed by a car with a mass of 2 350 kg if it is traveling at 125 km/h?

The velocity must be...