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Question:
WOULD A PERSON JUMPING ON THE GROUND HAVE ANY EFFECT WHAT SO EVER ON THE MOVEMENT OF THE EARTH? MY FREIND HAS STATED THAT IT WOULD MOVE THE EARTH BECAUSE OF NEWTONS LAW ( ACTIONS HAVING EQUAL ) MY ARGUMENT IS THAT THE EARTH IS NOT A STATIONARY DEAD OBJECT, IT IS LIVING WITH MILLIONS OF EVENTS HAPPENING ALL THE TIME I.E. VOLCANOES ETC AND IT IS ALSO MOVING THROUGH SPACE. ALL THIS WOULD MEAN AN ACTION BY ONE TINY OBJECT SUCH AS A PERSON JUMPING OULD HAVE ALMOST 0 EFFECT PERHAPS 000000000000000000000000000000000000000000000000000000000000000000000000000 000000000000000000000000000000001



Replies:
Kevin,

It sounds to me like you are both right. Newton's law certainly holds despite the large differences in mass. The fact that the earth has millions of such events occurring all the time is irrelevant, each one has an effect. Because of the large differences in masses, a person jumping on the earth would have a very tiny effect on the earth's motion.

Remember also that there are two forces acting when a person jumps. There is the force from the person's legs propelling them upward and there is the force of gravity. The center of mass of the earth/person combination will stay the same. When the person jumps the earth will be pushed downward while the person is pushed upward. Gravity will act to bring the two back together with the same center of mass that they had at the beginning of the jump. Essentially there will be no lasting effect on either of them.

Bradburn



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