Physics is the science that studies motion and matter and how both work with forces and energy. It is a really big subject that has a lot of different “branches” of scientific study that include motion, sound, waves, electricity, light, sound, and even astronomy.

This science covers the tiniest particles and atoms all the way to the largest objects in the universe.Momentum is what scientists call the measurement of a mass in motion. All objects that are moving have momentum.

An example of this might be riding along on your bicycle and then hitting a rock that stops your bike. You would find yourself continuing to move, even though the bike has stopped. This movement is called “momentum.”

Scientists in physics use an equation to show momentum: an object is equal to the mass times the velocity or momentum = mass * velocity. They use the letter “p” to represent momentum so that the equation is: p = m * v.  The “m” is mass and the “v” represents velocity.

You know from riding in a car that you have more momentum than you would if you were running down the street.

Newton's apple in Einstein's elevator

But if you were running at the same velocity as the car, the car would still have more momentum because it has a greater mass than your body. Both the mass and the velocity can alter the momentum.

Measuring momentum

A vector is a measurement that has a start and finish and goes in one direction. Both momentum and velocity are considered to be vectors. This means that momentum also has a direction.


Everyone knows about collisions. This happens when two objects bump into each other. It has happened to most of us when we bump into a door, a skateboard hits a rock in the road, or even when two cars hit each other in an accident.

In each case, each object exerts forces on the other object for a short time. If you text, you are experiencing a type of collision when your fingers touch the phone pad.

Conservation of Momentum and collisions

Scientists have created a theory in physics called the law of momentum conservation. It is the description of what happens to momentum when two objects collide.

The law states that when two objects collide in a closed system, the total momentum of the two objects before the collision is the same as the total momentum of the two objects after the collision. Each object’s momentum can change, but the total is still the same.

Interesting Facts about momentum and collisions:

  • There doesn’t seem to be a clear reason why the letter “p” is used for momentum. Some scientists think that it may have come from the Latin word “petere” which translates to “go towards”. The must have decided on this because the letter “m” was already in use for “mass.”
  • Energy is never destroyed, it is only altered or changed.
  • An elastic collision is a type of collision where none of the kinetic energy is lost.
  • An inelastic collision is where some of the kinetic energy of the colliding body is lost and then converted into another type of energy such as sound or heat.
  • Some of the objects in space such as stars or planets, have momentum that allows them to continue to go in the same direction until something comes along to push them in another direction or even stop them completely.
  • Our Sun continues to go around and the Earth continues to orbit the sun.
  • On Earth, friction with water or air can slow down or stop an object.
  • Examples of momentum that increases can include the development of a tornado where the wind increases in velocity or the snowball that rolls down the hill gaining speed as its mass gets bigger.


What is a vector?
a measurement that has a start and finish and goes in one direction

Why didn’t scientists use the letter “m” for momentum?
because it was already being used to define “mass”

What two properties can affect moment?
mass and velocity

What is the definition of momentum?
the measurement of a mass in motion

What is a collision?
when two objects bump into each other

Name an object that has momentum that continues in the same direction until something comes along and pushes it in another direction or stops it.
planets, stars