Why an object moves if the force applied is equal and opposite?

Answer 1

The reaction force acts on the object causing the original force, not on the object the reaction force is caused by. So there is only one force acting on each object, and they both move (unless there is another force outside this pair preventing such movement).

Answer 2

It won't!

It certainly won't if it is fixed down. And certainly then force and reaction are equal. If it is not fixed down the reaction is provided by mass x acceleration. Inside a rocket engine, the explosive pressure on the wall opposite the exhaust provides a force which is matched precisely by mass x acceleration and the rocket takes off. This idea is known as d'Alembert's principle. If the exhaust end of the rocket were to be blanked off by a door, there would be a force on the rocket in that direction too, and no net force to drive the rocket.

A falling body of mass M experiences gravitational force F. It is observed to accelerate at an acceleration g. So the force must be F = mass x acceleration = Mg. This force is called the weight. It all fits nicely because the force Mg causes an acceleration given by Mg=Ma so that a=g. All objects fall with the same acceleration (ignoring air resistance) because although the gravitational attraction for a heavier article is greater (weight), the inertia (Mass) is greater in exactly the same proportion.

Finally if you, draw a diagram of forces for a falling object you get Mg downwards, and Ma upwards (d'Alembert's principle represents an inertial force in the opposite direction to the acceleration). This principle can be used usefully to reduce problems with accelerated motion into a problem of "static" forces (Ma up is balanced by Mg down).

Answer 3

If the two forces are not acting at the same point, then it can create a torque which would cause the object to spin. Think of a see saw. If two people weigh the same, at the same distance away from the pivot, then both forces are down (same direction, not opposite), but the see saw is balanced and doesn't move. However, at the pivot point, the two torques are opposite (one clockwise, the other counterclockwise).

If the object is already in motion, then equal and opposite forces will cancel each other, so that there is no net acceleration, but the object will continue in the same direction as it was going.

Answer 4

A body will accelerate (its velocity changes) if the net forces ON THE BODY, that is, the vector sum of all forces, are non-zero.

Action and reaction are unrelated: the action and reaction forces act ON DIFFERENT BODIES. Forces will always come in pairs, but the sum of forces on an individual object can still be non-zero.

Answer 5

body will move due to reaction