Before the time of Galileo and Newton, many scientists had asked themselves, "What is the natural state of motion?" According to Asistotle's theory of motion, which had prevailed some fifteen centuries after his death, an object will required a force to keep it in motion. That is, the natural state of an object was one of rest, with the exception of celestial bodies, which were naturally in the motion. It was easy to observe that a moving objects tended to slow down and come to rest, so a natural state of being at rest must have seemed logical to Aristotle.

Galileo has studied motion using a ball rolling onto level surface from an incline plane. The smoother he made the surface, the further the ball would roll to. (See below) He reasoned that if he could make a very long surface perfectly smooth, there would be no resistance to stop the ball; and it would continue in motion indefinitely or until something stop it. Thus, contrary to Aristotle, Galileo concluded that objects could naturally remain in motion rather than come to rest at a point.

 If the level surface could be made perfectly smooth, how far do you think the ball will travel?

NEWTON'S FIRST LAW

Newton recognized this phenomenon and incorporated Galileo's result in his first law motion, which is stated below.

Uniform motion in a straight line means that the velocity is the same (constant). Thus another way to state Newton's first law of motion is to say that the natural state of motion is at a constant velocity. If the constant velocity is equal to zero, we say that the object is at rest.

NEWTON'S SECOND LAW

In our initial study of motion, acceleration was defined as the time rate of the change in velocity. Nothing was said about what cause accelerations, only that the change in velocity was required. So what causes an acceleration?

Newton's second law clearly implies that the acceleration depends only on force and mass. Acceleration does not depend on the kind of force, whether it is gravitational, electrical or whatever. Nor does the acceleration depend on the shape of the object, whether is ti lead or wood, or for the that matter, its state, whether solid, liquid, or gas.

A "NEWTON"

The word "Newton" not only mean the great scientist Isaac Newton, but also a kind of energy. A Newton (N) is the force needed for accelerated a 1 Kilogram (kg) object at a rate of 1minute per second square. For example if a car weights 2 kg, then you would need 2N to be able to accelerate the car.

NEWTON'S THIRD LAW

The statement above is Newton's third law. "If you press on a stone with your finger, the finger is also pressed upon by the stone," a illustration given by Newton.

The rocket motion is also an good example of Newton's third law. The exhaust gas is accelerated from the base of the rocket, and the rocket accelerates or move in the opposite direction. A common misconception is that the exhaust gas pushes against the launch pad to accelerate the rocket, but if this statement is true, then there would be no space travel. Since there is nothing to be pushed upon in space. The correct explanation is on of action (gas going out at the back) and reaction (rocket Propelled forward). The gas (or a gas particle) exerts a force on the rocket, and the rocket exerts a force on the gas that is coming off the rocket.

 The rockets and exhaust gas exert a force on each other and are accelerated in opposite directions.