# Changes

## Newton's third law of motion

, 00:15, 18 August 2012
Examples
| Any object close to the surface of the earth || the object and the earth || The gravitational force exerted by the earth on the object, and the gravitational force exerted by the object on the earth || The two forces are equal in magnitude and opposite in direction. In other words, the "downward" force experienced by the object due to gravity has a corresponding "upward" force experienced by the earth. However, due to the huge mass of the earth, the resultant acceleration of the earth is too negligible to be noticed.
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| A block resting on a fixed horizontal floor || the block and the floor || the upward normal force exerted by the table on the block and the downward normal force exerted by the block on the floor || The two forces are equal in magnitude and opposite in direction. The normal force adjusts in magnitude to counteract other forces, in this case gravitational forces, so the block experiences no net acceleration and remains stable (by [[Newton' s first law of motion]]). The floor does not accelerate downward either, presumably because whatever mechanism is fixing it is also generating forces that counteract the downward force exerted by the block.|-| The earth and the moon || the earth and the moon || The gravitational force exerted by the earth on the moon, and the gravitational force exerted by the moon on the earth. || The two forces are equal in magnitude and opposite in direction. The effect on the moon -- the moon orbiting the earth -- is more visible because the moon has less mass. The effect on the earth -- including tides -- is less salient because of the larger mass of the earth.
|}

==Misconceptions==