Newton's Three Laws of Motion

Force

Force is the push or pull that one object exerts on another. If you push a book across the table, the power that you use to push that book is force. If you pull a shade down on a window, the power that you use is force. Force can affect an object in one of three ways. Force can start the object moving or stop the object from moving. Force can cause the object to move in a different direction. Force can change the speed of the object's movement.

Newton's Three Laws of Motion

All moving objects on Earth are governed by Sir Isaac Newton's three laws of motion. These laws are as follows:

1st Law: Objects at rest stay at rest and objects in motion stay in motion unless acted on by a force.

2nd Law: Acceleration of an object depends on its mass and the size and direction of the force acting on it.

3rd Law: Every action has an equal and opposite reaction force.

Earth's Gravity

Gravity is a force that is explained only in terms of its effects rather than its actual cause. For some reason, objects tend to draw toward one another in direct proportion to their size, and they tend to loose affraction in proportion to the square of the dis­tance that separates them.

The greater the two masses involved actually are, the more gravity is exerted. This explains why your gravitational affraction to the earth is greater than your gravitation­al affraction to the wall closest to where you are sitting. You are drawn toward the center of the earth, causing a friction that far overcomes your gravitational affraction for the wall. Thus, you sit in a chair and do not go sliding into the nearest wall.

When a force is exerted on you that resists gravity, that force causes you to have weight. The floor, for instance, exists between you and the center of earth's gravity. If you place a scale between you and the floor, the push you have against the scale is measured as your weight. However, if the floor were to vanish, you would begin to fall freely with respect to gravity, and the scale would read zero. This condition, the condi­tion in which gravity acts freely on an object, is called weightlessness. Weightlessness is the condition in which astronauts exist as their space shuffle continually falls toward the earth (gravity is acting freely).