Formula for Mass: Definition & Examples

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  • 0:00 What Is Mass?
  • 1:13 Calculating and Measuring Mass
  • 4:25 Lesson Summary
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Lesson Transcript
Instructor: Ryan Hultzman
In this lesson you will learn about mass and how it is tied to Newton's Second Law of Motion. You will learn how to calculate mass and how to measure mass through a few examples.

What Is Mass?

A bowling ball, a tennis ball, and a ping pong ball sit on three separate scales. Which one would you guess will have the largest reading on the scale? The bowling ball, of course. We know from experience that a bowling ball is heavier than a tennis ball or a ping pong ball. We would also correctly guess that the ping pong ball will have the smallest scale reading. What the scale is reading is the mass of each object. Mass is a measure of how much stuff an object has. Mass is a scalar quantity; therefore, it only gives us information about the magnitude or the amount of stuff in an object.

This amount of stuff does not always have to do with the size of an object. For instance, two bricks may have identical dimensions, but if one brick was made out of lead and the other was made out of plastic, the lead brick would be more massive. Mass is measured in grams (g) and kilograms (kg). Mass is often mistaken for weight. Weight is a force that depends on the mass of the object and the acceleration of gravity. They are two different things. If you go to the moon, your mass will be unchanged, but your weight would decrease because the acceleration of gravity on the moon is less than that of the earth.

Calculating and Measuring Mass

There are two ways to determine the mass of an object. The first method involves some mathematics. Mass is introduced in physics in Newton's Second Law of Motion. In that law, Newton states that when you add up all of the forces acting on an object, called sum of forces, or net force, and that sum does not add up to zero, then that object is accelerating. This law states that the force acting on an object is proportional to the acceleration experienced by an object. This means that if the force increases, the acceleration increases, and conversely, if the force decreases, then the acceleration decreases. The constant of proportionality between force and acceleration is called mass. More specifically, it is called inertial mass.

Inertial mass is defined as an object's resistance to acceleration. This means that the larger the inertial mass, the harder it is to accelerate that object. Let us look at our bowling ball and ping pong ball again. If I exert the same amount of force on both balls, which object will have a greater acceleration? The answer is the ping pong ball because it has less inertial mass and hence, it will be easier to accelerate the ping pong ball than the bowling ball. This set of equations gives us the formula for calculating the mass of an object if we know the force acting on it and the acceleration of the object:


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