GRAVITY
The universe is made of matter. Matter is held together and moved by forces. One of the basic or fundamental forces is the gravitational force. Any piece of matter from a pinhead to a planet has this gravitational force. It pulls or attracts other matter. The biggest large lump of matter in our daily lives is the Earth. Its gravitational force pulls us and other objects towards it, keeping our feet on the ground. The Earth’s gravitational force is also called gravity.
Gravity means that all matter, from the minute particles that make up atoms to the biggest stars, attracts each other. The nearer an object, the stronger it’s gravitational force on other objects. But the force becomes weaker with increasing distance. Earth is very big and very near, so for us its gravity is very strong. However, a few hundred kilometres above the surface its gravity is weak and objects may drift off into space.
The Earth’s gravity gives matter and objects what we call weight. A big book is weighty because it is being pulled downwards by Earth’s gravity and we have to counteract this force with our muscles when we pick up the book. However, weight varies according to the strength of gravity, and the strength of gravity depends on the amount of matter (and its density) in the two objects that attract each other. We are used to the weight of objects on Earth. The Moon has less matter than Earth, so its gravitational force is less. On the Moon the book would weigh less – about one-sixth of what it weighs on Earth. On a star consisting of vast amounts of matter the book would weigh many tonnes.
Weight varies with gravitational force but mass does not. Weight is a measure of the gravitational force pulling on an object. Mass is a measure of the amount of matter in the object – the numbers and types of atoms. On the Earth, Moon or a star, the book would weigh different amounts, but it would always have the same mass.
Picture Credit : Google
