What Is Momentum in Physics?

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What Is Momentum?

You have likely heard the word momentum before.

For example, if a basketball team is said to have a lot of momentum, it is a team that is performing well, has high energy, moves fast, and is harder to stop!

This is no different than what the word momentum means in physics. Momentum is mass in motion, which means that any moving object has momentum.

Based on this definition, there are two factors that determine the amount of momentum an object has: mass and velocity.

Mass (m)

Mass measures the amount of matter in an object. The more massive an object is, the greater its momentum and the harder it is to stop.

A bowling ball is, obviously, more massive than a baseball and, therefore, has higher momentum.

Velocity (v)

Velocity is the rate of change in position over a period of time. In simple terms, it tells you how fast you are moving and in what direction.

The faster an object moves, the higher its momentum and the harder it is to stop. Consider how hard it would be to catch a baseball traveling at 50 miles per hour compared to one traveling at 20 miles per hour.

To understand how mass and velocity can affect the momentum of an object, watch What is momentum? | Force and laws of motion | Class 9 Physics (CBSE/NCERT) from Toppr:

Measuring Momentum

Mathematically, momentum (p) is expressed as a product of mass (m) and velocity (v):

p = m ⋅ v

Although the reason why the letter p was used to represent momentum is not completely known, it is likely because Sir Isaac Newton was working on his book, Principia, at the time. He used the term impetus to describe the quality of a moving object. The word impetus comes from the Latin word petere, which means to go or to seek.

Regardless of why p was chosen, it is a convenient symbol for momentum because m is already assigned to mass.

The SI (metric) unit of momentum is kilograms meter per second (kg m/s) because the standard unit of mass is kilograms (kg) and velocity is meters per second (m/s).

An object's momentum is determined by the amount of its mass and its velocity (p = mv). Even if an object is very small, it can have a high momentum if it is traveling at a high speed. One example of this is a bullet. Likewise, a slow moving truck can have high momentum because if its mass.

Let's practice how to use momentum equations in simple problems.

Consider a 100-kg halfback initially moving at 7 m/s. You want to compare his momentum when he runs at 8 m/s and 9 m/s.

When solving problems like this, organize your work with the GRESA format: Given, Required, Equation, Solution, and Answer.

For this simple problem:

This simple problem shows that when the velocity increases, the momentum increases.

This means that momentum is directly proportional to velocity. Because the mass in this case is the weight of the halfback, it will not change.

If you would benefit from learning a bit more about momentum, check out the following resources:

• Momentum, from the Physics Classroom
• Physics for Kids: Momentum and Collisions, from DUCKSTERS™

When you are ready to test your understanding of momentum in physics, head over to the Got It? section.