Question

how do newton's law work in inertial frame of reference.....
plz..expln the first law...

Answer 1

An inertial frame of reference is basically a frame which has a velocity relative to a reference frame, say the ground frame. It has no acceleration relative to ground frame. So basically if you were riding a bike and you were moving at a constant speed with no acceleration the person on the road would observe that no net external force was acting on you since your velocity is constant. In your frame of reference you would observe that the person on the ground is moving with a constant velocity relative to you. Since that person too has no acceleration in your frame you would conclude that no external net force is acting on said person.
Newton's first law states the property of inertia of a body saying that a body perseveres to stay in its state of motion unless a net external force acts on the body to accelerate it. That is a body at rest will stay at rest and a body moving with uniform velocity will move in a straight line with the same uniform velocity unless an external force acts on it. It holds in an inertial frame but not in a non-inertial(accelerating) frame of reference.