As a ball falls, the force is the pull of Earth's mass (gravitational force) on the ball. What is the reaction force?

Question

akshay_budhkar · Answer

i dont think there is any reaction force.. if there was  then the ball would have stopped midway right?? Well in real life situation air resistance can be a reaction force but in classical physics i dont think there is any?

anonymous · Answer

Yes there is no reaction force for gravitation force.

agentjamesbond007 · Answer

Not even the normal force?

akshay_budhkar · Answer

normal force is when the object is rested on a surface and the surface exerts a force normal that is perpendicular to it

akshay_budhkar · Answer

currently u have no surface exerting force on it in the air

akshay_budhkar · Answer

however in space the circular force compensates for the gravitational force and so satellites remain in the sky.. you take that as an example :D

turingtest · Answer

I'm pretty sure the action force is Earth pulling the object down, the reaction force is the object pulling Earth up. Since the object has a tiny mass compared to Earth, it is the item that sees the acceleration without it's own influence coming into play.

akshay_budhkar · Answer

i believe the question was aimed from the point of view of the object and not that of the frame altogether so the object pulling the earth cannot be conducive in this context right? And yes it is pretty negligible as the weight is small so anyways the force is not considered

turingtest · Answer

Probably, that makes sense in this context.

jamesj · Answer

The question asks what is the reaction force.  What TT said first is exactly right.  Just because that reaction force isn't acting on the mass that we perceive as falling doesn't matter.

Consider by analogy two electric charges of equal charge a distance a meter apart.   The move away from each other; the force on one is opposite and equal to that on the other.  The reaction force acts on one object but not the other, and which one you decide is the reaction and which the 'original' is completely arbitrary.

akshay_budhkar · Answer

but in that case you take the frame of reference as the two particles.. in this case you r taking just the object.. while solving problems of mechanics you never consider earth in your frame,do you? In electrostatics you do consider both the particles so the reaction force is defined

jamesj · Answer

Only because the distance the earth moves is trivial.  But that doesn't mean the force isn't there.

akshay_budhkar · Answer

i never said that.. i just argued in context of the frame and nothing else hehe.. ofcourse the force exists.. i just said th question seems to be aimed from the frame of the ball as it is generally done and so i replied saying none.. Even you r right :D

agreene · Answer

$$F=G\frac{m_1m_2}{r^2}$$
Frame of reference makes no difference if we choose to adopt Newtonian methods.