Isaac Newton's three laws of motion. 

Jump to: Second Law  Third Law  Isaac Newton GRAVITY STUDENT NOTES  
Isaac Newton's First Law of Motion 

The first law deals with forces and changes in velocity. For just a moment, let us imagine that you can apply only one force to an object. That is, you could choose to push the object to the right or you could choose to push it to the left, but not to the left and right at the same time, and also not up and to the right at the same time, and so on. Under these conditions the first law says that if an object is not pushed or pulled upon, its velocity will naturally remain constant. This means that if an object is moving along, untouched by a force of any kind, it will continue to move along in a perfectly straight line at a constant speed. This also means that if an object is standing still and is not contacted by any forces, it will continue to remain motionless. Actually, a motionless object is just a special case of an object that is maintaining constant velocity. Its velocity is constantly 0 m/s. Now, what about if there is more than one force on the object? You really can push an object, say, to the left and down at the same time, so, what happens then? Under these conditions we must realize that a group of forces on an object adds up so that all the forces appear to the object as one force. This one force that is the sum of all the forces is called the NET FORCE. The word net in this context means total. It is this net force that may change the velocity of the object. Let us look at some examples. Imagine that two forces act at the same time on an object. One is a very strong force to the left, and the other is a weaker force to the right. These two forces add up to one net force. Since the force to the left is stronger, the net force is to the left. This net force to the left will cause the velocity of the object to change. The object experiences this one net force as if this was the only force pushing it, although, actually, there are two separate forces present. The net force is the total force. It could be the sum of two forces or more than two forces. If only one force acts upon an object, then this one force would be the net force. If the net force on an object is zero, then the object experiences no velocity change. If the net force on an object is not zero, then the object will show a change in velocity. Lastly, this net force must be external to the object. The net force can not come from the object itself. You could not, for example, put on ice skates, stand on a frozen pond, push on your back by reaching around with your arms, and expect to get going. Although if someone else came up from behind and gave a you a shove, then your velocity would change. Newton's first law of motion contains the same information as Galileo's explanation of inertia. Galileo stated. INERTIA is a property of matter. It is that property of matter, which opposes changes in velocity. Simply stated, an object will not change its velocity spontaneously. That is, if something is moving along at a constant speed in a straight line, it will continue to move along at the same constant speed in the same straight line. It will not, all on its own, speed up, slow down, or change direction. Something else must push on the object to speed it up, slow it down, or change its direction. What does this sound like? Newtons First Law


Isaac Newton's SecondLaw of Motion 

Newton's second law of motion explains how an object will change velocity if it is pushed or pulled upon. Firstly, this law states that if you do place a force on an object,
Secondly, this acceleration is directly proportional to the force. For example, if you are pushing on an object, causing it to accelerate, and then you push, say, three times harder, the acceleration will be three times greater.
Thirdly, this acceleration is inversely proportional to the mass of the object. For example, if you are pushing equally on two objects, and one of the objects has five times more mass than the other, it will accelerate at one fifth the acceleration of the other.


Law of Motion 

The third law states that for every force there is an equal and opposite force. For example, if you push on a wall, it will push back on you as hard as you are pushing on it.
