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Rene - the earth's orbit wouldn't be affected by everyone in China jumping off a chair at the same time. Sorry - it's a fun idea. Let's work this out quantitatively. Suppose when you hit the ground you hit with a force equal to twice your weight. Let's assume that the average mass of a Chinese person is 60 kg, and that there are 1.2 billion people in China. Total force on the Earth: (60 kg) x (9.8 m/s^2) x 2 x (1.2 X 10^9 people) = 1.41 x 10^12 N Acceleration of the Earth this this force produces: a=F/m(Earth) = (1.41x10^12 N)/(6.0X10^24 kg) = 2.4 x 10^-13 m/s^2. This is very very small. For comparison, let's calculate the acceleration of the Earth due to the gravity of the Sun, which is what keeps the Earth in its orbit: a=F/m(Earth)=GM(Sun)/r^2 a = (6.67X10^-11 N m^2/kg^2) x (2.0 x 10^33 kg)/(1.5 x 10^11 m)^2 a = 5.9 x 10 ^-3 m/s^2 This is also a pretty small acceleration but it's a lot larger than what you could get from people jumping off chairs! Pauline

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