Force In The Term Of Mass And Accelaration

[Kratos]

we study that F=ma but even when any object is at rest inside the earth and there is no acceleration in that body still it experience gravitational force can you please explain

[scrunge999]

If an object is at rest, the net force acting on the object is zero.

[bhg481]

When you stand on the surface of the earth the gravitational force acting on you is balanced by a reaction at the earth's surface, so the net force acting on you is zero. The same applies if you are below the surface of the earth. The reaction force can be measured by standing on a bathroom scale.
Note that if you are not standing on a firm surface the reaction force may not be equal to the gravitational force, in which case you will sink towards the centre of the earth.
Think of an iron ball, mass m, sitting on the surface of the earth - reaction force = ma. Now put in on the surface of some water; reaction force is less than ma (Archimedes' principle), so ball sinks.

[jim360]

If it helps to clear things up then remember that the equation F=ma is meant to be a simplified version of the "full" equation. In particular, the "F" on the left-hand side stands really for "sum of all forces" that are acting on the object you are interested in. It's possible for the sum of all forces to be zero because there *are* forces acting, but they are acting in opposite directions so that in the end they balance out exactly. That would lead to situations where we still experience gravitational force but with no acceleration.

[Kratos]

thanks all of you @bhg481 and @jim360 your answers really helped.