THE 1ST LAW

Newtons 1st law of motion states that a body's state of rest or uniform motion in a straight line will only be changed by a resultant external force acting on the body. Strictly speaking it is really a definition of what the quantity called force is.

THE 2ND LAW

Newtons 2nd law of motion states that, when an resultant external force acts on a body, it is accelerated in the direction of the force; the magnitude of the acceleration is directly proportional to the force and inversely proportionanal to the mass of the body. Because Force is defined by these laws the constant of proportinality was taken as unity.

THE 3RD LAW

Newtons 3rd law of motion states that, when A exerts a force on B, B exerts an equal and opposite force on A. The 3rd law always deals with forces acting on differemt bodys.

• Force is a vector quantity as it is the product of a scalar (mass) and a vector (acceleration)
• The 2nd law can be summerized as ΣF = m a, ΣF is the vector sum of all forces acting on the body.
• Modern cars, now have a crumple zone built into the front end which crumples up and so reduces the rate of decceleration and hence force exerted on the rest of the car and passengers.