The science of mechanics is based on three natural laws relating force and motion. These were clearly stated for the first time by Sir Isaac Newton [1642 – 1727] and were published in 1686 in his Philosophiae Naturalis Principia Mathematica. Newton’s three laws relate an object’s acceleration to its mass and the forces acting on it. A modern wording of Newton’s laws follows:
I. Newton's First Law of Motion: Every object continues to be at rest or in a state of uniform motion unless acted on by an external force.
This we recognize as essentially Galileo's concept of inertia, and this is often termed simply the "Law of Inertia".
To say that something is moving always implies a specific frame of reference. An inertial frame of reference is one in which Newton’s first law of motion holds.
II. Newton's Second Law of Motion: Newton's second law of motion explains how an object will change velocity if it is pushed or pulled upon.
The rate of change of momentum of a body is directly proportional to the applied force acting on the body.
Firstly, this law states that if you do place a force on an object, it will accelerate, i.e., change its velocity, and it will change its velocity in the direction of the force.
It accelerates in the direction…………..
That you push it.
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.
If you push twice as hard…………..It accelerates twice as much.
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.
If it gets twice the mass……………..It accelerates half as much.
III. Newton's Third Law of Motion:
The word force is used to describe the interaction between two objects. When two objects interact, they exert force on each other. Newton’s third law states that these forces are equal in magnitude and opposite in direction.
For example, if you push on a wall, it will push back on you as hard as you are pushing on it.
If you push on it…………………
It pushes on you.