# Am I right to conclude this about mass?

## Main Question or Discussion Point

When a force applies on a freely moving mass, it opposes the motion, to oppose the motion there should be a force. So we can conclude that if a mass is made to move, it applies a force on the force that applies on it
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If any moving mass is set to motion, without collapsing itself (or breaking), it can be said that the normal reaction given by the mass is equal to the force that applies on it.

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Pengwuino
Gold Member
Yes, exactly Newton's Third Law.

When a force applies on a freely moving mass, it opposes the motion, to oppose the motion there should be a force.
You are saying a force on a mass exists if and only if there is an acceleration (in your terms, if "it opposes the motion"). This is Newton's First Law.

dE_logics said:
So we can conclude that if a mass is made to move, it applies a force on the force that applies on it.
It doesn't make sense to "apply a force on a force". Instead, we should say "apply a force to an object causing that force". As Pengwuino said, this is Newton's third law. I wouldn't say we can "conclude" this is true just because what you said before was true, though.

Ok...thanks a lot people!

Force without motion does no work. A mass M on a table has a downward force Mg, and the table has an equal opposing upward force -Mg, so the two forces balance , and no work is done.