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This question already has an answer here:

I read this example of pushing a table with your hands. So the force is applied on the table to push and the table exerts the same amount of force on our hands.

My question is, if the forces are equal and opposite, how does the table move on our push? Don't they cancel out? According to newtons third law reaction force from the table is same right.

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marked as duplicate by John Rennie newtonian-mechanics Jan 5 '18 at 12:28

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  • $\begingroup$ Always concentrate on one body at a time. The table only feels a pushing force and possibly friction from the floor. Another body, your hand, feels force from the table. $\endgroup$ – npojo Jan 5 '18 at 11:23
  • $\begingroup$ But how does a balloon fly upwards when the gas inside it is released ? I see only one object involved in this experiment. $\endgroup$ – Yogi Jan 5 '18 at 12:38
  • $\begingroup$ 1) baloon 2) gas. $\endgroup$ – npojo Jan 5 '18 at 13:54
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When pushing on the table, an equal but opposite reaction force is applied back. Yes.

But the push and the reaction force are on different objects. The push is felt by the table. The reaction is felt by the person.

This is a general confusion often seen, so remember this in all future work. An astronaut pushing himself away from his spaceship is actually not pushing himself away - the spaceship is pushing him away with the reaction force. And his push makes the spaceship move as well, although only slightly.

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  • $\begingroup$ Thansks, But how does a balloon fly upwards when the gas inside it is released ? I see only one object involved in this experiment $\endgroup$ – Yogi Jan 5 '18 at 12:34
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    $\begingroup$ @Yogi You can think of the air inside as the other "object". The air is pushed down. The ballon is pushed up. $\endgroup$ – Steeven Jan 5 '18 at 12:54

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