# Mass, Weight & Gravity

Some students are confused by the concepts of mass and weight. Mass is actually a very difficult concept to wrap your head around and scientists themselves do not fully understand it. We usually define mass as a measure of the amount of matter an object has. But what is matter? Matter is stuff that has mass and volume. So we are using matter to define mass, and mass to define matter. Believe me, your English teacher would never go for that. Luckily, even though we don’t fully understand mass, we can still measure it.

Weight is a much simpler concept to understand. Weight is a force. When we say that an object weighs 10 pounds, what we are really saying is that the Earth is pulling on that object with 10 pounds of force. In common usage, we often use mass and weight interchangeably. That’s because how hard the Earth pulls on an object depends on its mass. The more mass an object has, the harder the Earth will pull on it.

I weigh about 150 pounds. That means that the Earth is pulling on me with a force of 150 pounds. That force is what is holding me to the surface of the Earth, and when I jump, it is the force that pulls me back down.

The force that the Earth is exerting on me — the force that is pulling me down toward the Earth’s center — is the force of gravity. Funny thing is, most people don’t realize that while the Earth is pulling on me with 150 pounds of force, I’m also pulling on the Earth with 150 pounds of force. That’s right. I’m pulling on the Earth just as hard as the Earth is pulling on me.

And that’s not all. If you weigh 100 pounds and are standing 10 feet away from me, then I am pulling on you with about 0.00000007 pounds of force and you are pulling on me with about 0.00000007 pounds of force. We just don’t notice it because the force is so small. All objects with mass are attracted to one another through the force of gravity.

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