Many forces that act on objects cannot be seen. The gravitational force of the earth pulls an object down to the earth. A famous scientist named Sir Isaac Newton discovered this kind of force in 1666 when he was 23 year old.
Falling apple
Isaac Newton
Newton puzzled over this problem when sitting in an orchard. He suggested that the apple and the earth had invisible force that pulled other objects toward them. The earth and the apple had force pulling each other. The earth is so huge that it could not move, but the apple was much smaller than the earth. Therefore, the apple was pulled down to the earth. This force is called gravity.
Can we see gravity and can we observe the effect of the gravity?
A man lifting an and object exerts force against the earth’s gravitational force. The crane in the picture also pulls a box in an opposite direction of gravitational force.
Forces can be measured in several ways. A simple method can be made by using force meter. It contains a spring connected to a metal hook.