We have learnt about the motion of objects based on the definition of displacement, velocity and acceleration.
A vegetable vendor applies force to push the cart, a driver applies force either to stop the car or to change the speed or direction of motion and a football player kicks the ball to set it in motion.
Any object can be made to move by the application of force. Many forces can act simultaneously on a body.
Aristotle and other medieval thinkers believed that the natural state of bodies is the state of rest. Galileo opposed this concept.
It is clear from Galileo's experiments that all objects have a tendency to continue in their state of rest or of uniform motion until an external force acts on it.
A body continues to be in a state of rest or of uniform motion along a straight line unless an external force acts upon it.
Newton's second law of motion states that rate of change of momentum is directly proportional to applied force and takes place in the same direction as the applied force.
In a cricket match a fielder moves his arms back while trying to catch a cricket ball because if he tries to stop the fast moving ball suddenly then the speed decreases to zero in a very short time.
To every action there is an equal and opposite reaction.
Couple two spring balances A and B as shown in the figure. When we pull the balance B both the balances show the same reading indicating that both the action and reaction forces are equal and opposite.
When a bullet is fired from a gun, the gases produced in the barrel exerts a tremendous force on the bullet (action force). As a result, the bullet moves forward with a great velocity called the muzzle velocity.