Reaction of a Surface
When an object is resting on a surface it pushes down on to the surface because of it's weight.
This creates an equal reaction force pushing up to the object.
If an object is travelling at a steady speed, the forces acting upon it are equal.
This applies to all moving objects un less it changes speed or direction.
Resultant force is the overall force acting on an object.
It decides the motion of an object.