It is advantageous to run before taking a long jump. Why?

When we run, our body gains inertia of motion due to which it wants to be in motion continuously. When we take long jump our body has the tendency to be thrown forward more.

NEWTON'S SECOND LAW OF MOTION

The Second law states that the rate of change of momentum is directly proportional to the applied force and the change takes place in the direction of the force applied.

If u= initial velocity,
v=final velocity,
t= time taken to change the velocity from u to v,

Then
Initial momentum = mu
Final  momentum=mv

So change in momentum = mv-mu =m(v-u)
Hence the rate of change of momentum = m(v-u)/t

Therefore F= m(v-u)/t
  F=ma.
                            

NEWTON'S THIRD LAW

The law states that "to every action there is an equal and opposite reaction and these forces act on different bodies"

Examples

1. When a rocket is launched, the burnt gases are expelled down from the rocket body. Here action is on gases by the rocket body. Hence the gases exert an equal an opposite force on the rocket body in the upward direction. This is the reaction force. With this force rocket moves in upward direction.

ACTION...on the gases by the Rocket body.
REACTION..On the rocket by the burnt gases.

2. When a gun fires bullets, action is on the bullets by the gun and reaction on the gun by the bullets. Gun recoils back due to the reaction.

ACTION: On the bullets by the gun..
REACTION...on the gun by the bullets