Question

Give an example where two equal and opposite forces don't form an action-reaction pair. (Class 9 Physics- Chapter: Forces and Laws of Motion.)

Answer 1

• A cube acted upon by two equal and opposite forces

Take a huge cube. Imagine that from one side a person is pushing it by applying an amount of force, say 10 N. On the side opposite to it, another person is pushing the cube with same force, i.e. 10 N. Here, on the whole, the cube is acted upon by two equal and opposite forces. But, these equal and opposite do not form action-reaction pair.

So, the above given example is the right example for this question.

Few terms related to this chapter:
Force: A push or pull that changes or trends to change the shape, size, direction of motion, state of rest, state of motion, etc.

State of rest: An object is said to be in state of rest when it does not change its place with respect to it's surroundings.

State of motion: An object is said to be in state of motion when it changes its place with respect to it's surroundings.

Answer 2

• two equal and opposite forces don't form an action-reaction pair.

The main reason is that the action and reaction forces are NOT on the same object.

For example, if my hand pushes a block across the floor, the action-reaction forces are the hand pushing on the block and the block pushing back on the hand. If you want to know whether the block accelerates you must look ONLY at the forces action ON the block. Those might be the hand on the block and friction caused by the floor acting on the block. If the hand force and the friction force are equal to each other then the block won’t accelerate. If the hand force is bigger than friction, then the block will accelerate.

Will my hand accelerate? Only if the force exerted by my arm on my hand is bigger than the block pushing backwards on my hand.

hope its help you sir