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I am new to physics and I understand gravity is a pulling force.

Let's assume a ball has been placed on the ground. Does gravity has any role after I placed an object (e.g. ball) on ground?

Sorry, if I asked something silly or the question was wrong.

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  • $\begingroup$ How about: forcing you to exert an effort to lift it? Note that nobody can tell you what the "role" of gravity is, nor that of electricity, magnetism, etc. They just "are". $\endgroup$ – hdhondt Mar 22 '16 at 9:28
  • $\begingroup$ Why would the gravity not have an effect? You feel it every day! $\endgroup$ – Jaywalker Mar 22 '16 at 10:14
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yes: the gravity maintain the ball on the floor. And if the ball is soft, it is maintained squeezed.

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  • $\begingroup$ there has to be some infinitesimal squeeze even for a non-soft ball; you need an inner reason for the force of interaction. $\endgroup$ – Ilja Mar 23 '16 at 11:58
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All object with mass has gravity. mass is the amount of matter in that object. That's why the weight of an object feels less on moon even if the mass is same. Earth's gravity is that force that attracts every objects towards its centre. Due to this gravity we could land on the earth surface even after we jump on it. without gravity, if we jump on the surface of earth we go upwards with uniform speed (neglecting air friction).

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The ball is in an equillibrium of two forces: the gravity and the pressing force from the ground.

You can say, that the two cancel out. But there is, in practice a difference, if you have no forces acting or some forces that cancel out. Because usually the forces change, if you change the system. In your example, the force from the ground gets smaller if you lift the ball a litte, because it is sqeezed less. The ball takes such a position, that the two forces are equal, because it experiences a net force and gets moved as long as they are not.

I hope the difference between cancelling forces and no forces is clear? - the former makes possible a stable system. With no force the smallest excitation would set the ball moving (with time arbitrarily far).

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The force of gravity never stops acting on the object. However, the gravity is balanced out by an equal and opposite normal force. Gravity simply keeps the object stuck to the floor. It does not stop existing; it is merely balanced and therefore has no overall impact on the object's motion. Hope this helps! -Alm.

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