The earth, like all other heavenly bodies, floats in space. “Weighing” such objects is not a simple thing as putting an object on a weighing-scale. When we speak of the weight of the earth, we mean the amount of matter that makes it up. This is called its mass.
The earth’s mass is about 6,600 trillion tons. To calculate this, scientists used a principle based on the fact that any two objects attract each other. The forces of gravity depend on these. The bigger the objects, the greater the force that pulls them together. Also, if the objects are closer the pull is greater, as the distance between them increases the pull decreases. By measuring the power of the earth’s attraction on a small weight, and then measuring the power of a big (one tone in weight) lead piece on the small weight, scientists can calculate the mass of the earth.