# Newton's third law of motion

Action has equal but opposite reaction then, why dont a ball keep on moving when made to move between two surfaces,should elasticity of surface,gravity and friction be mentioned in this theory?

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## migrated from math.stackexchange.comApr 2 at 11:49

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• You are talking about Newton's first law, i.e, inertia (ball should keep moving)

• This has absolutely nothing to do with the current tag.

• The first law doesn't need to explicitly mention friction, it already says "when no force is applied". It's upto you to keep track of external forces.

• This has been voted for migration to Physics but I doubt they will accpet such poorly formulated questions. You should probably read more on Newton's laws of motion.

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actually I am talking about 3rd law not 1st.if every action has equal reaction then why magnitude of force goes on decreasing? –  dipendra Apr 2 at 11:32
@dipendra I highly suggest you read the link provided. You have a serious misconception it seems. The magnitude of the force doesn't necessarily decrease, also the third law doesn't say anything about it. The third law is instantaneous. It talks about a particular instant of time. –  Sabyasachi Apr 2 at 11:37

I think Sir Issac Newton's laws works fine here.

1st law

Object will continue to be in rest or move in straight line
until a external force applied on it.


the ball starts/stops moving only when an external force applied on it.

2nd law

 F=ma


The ball uses the force 'F' applied on it to move in acceleration 'a' on direction of force.

3rd law

Every action has an equal and opposite reaction


the ball is stopped if an equal force applied on opposite direction of ball's movement.

But usually it stops due to friction/gravity/other obstructions which does not come into action exact opposite direction or exact force needed to stop ball. so it will move as long the above condition satisfies. also the friction reacts on exact force and direction opposite to ball's movement (same for all the obstructions ) and when these forces sums upto the force 'F' which used to made the ball move, ball will be stopped !

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The answer is that there is friction. Friction is a dissipative force, meaning that friction will cause energy losses. This causes the ball to stop rolling: in a vacuum that would not happen! These things can be taken into account when doing calculations.

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