Newtons 3. law. IF I use force on something and make it move, why don't I move as well?

Question

This is not a homework question. Just a concept I read from my physics book that I can't get the hang of yet.

Newtons 3. law

Says for every action there is an equal but opposite reaction. Meaning if you throw a ball on the ground, the force you use on the ball, the ground will have the same one but oposite direction.

What I don't understand is. Force=m*a. meaning if the force is the same, then why doesn't the ground move as well?

Some might say because the ground has a bigger mass but if force is equal to m*a, then the 3. law does not exist.

Or if you push a chair, then the chair has an reaction with same but opposite directed force, then why don't I move as well when pushing a chair?

Sorry for the weird question but I just can't get the hang of it yet. Please any help?

Answer 1

The ball exerts a force on the earth which is so the conservation of momentum says m1*v1 =m2*v2 where m1 and v1 refer to the ball and m2 v2 refer to the earth, solving this for v2 (the resulting velocity of the earth) gives v2=m1*v1/m2 recall that m2 is about 6*10²⁴kg. no matter how big m1*v1 is m2 so large the v2 can not be detected.

With regard to pushing the chair friction between your feet and the floor is what keeps you from moving. Think of you standing on ice (very low friction) pushing on the chair. Draw a free body diagram and lable all the forces and torques.

Regards

Jim