Weight while jumping in the air

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matt_london | 14:41 Thu 27th Sep 2007 | Science
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I watched mythbusters on Sunday and they performed an experiment which involved weighing a lorry carrying pigeons to see if the weight changed when the pigoens went from sitting on a ledge (inside the lorry) to flying in the air (also inside the lorry). The result was that the weight didn't change because the downward force exerted by the pigeons in order to fly was equal to their weight so there was zero effect on the scales.
If this experiment was done with people instead, who all jumped in the air at the same time, would the result be the same?


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From what I understand the lorry would not increase in weight regardless of what is inside: the combined weight is what would change.
If humans inside the lorry jumped simultaneously, then the stress on the suspension would slightly decrease, be it 1 person or 100. This lesser pressure would cause the truck to appear lighter than when the humans were sitting but the weight wouldnt lessen. I thought about this when weighing myself the other day: when pulling against the underside of the sink my 'weight' went up on the scales, although I didn't actually get heavier - I plan to do that this Christmas instead. Hope this helps :D
No, it would be quite different. At the point when the people actually started jumping the truck would be momentarily heavier until everyone was in the air, then the truck is lighter. When the people come down the truck will again be momentarily heavier until the kinetic energy is dissipated and the weight will once again be the same as before the people started their jump.

Now, if 100 people in a truck jumped all at different times the mean weight of the truck would be fairly steady.
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Thank you Wildood.
Can you explain why it would be heavier? Where does this extra weight come from?
Try standing on your bathroom scales - then jump.
Question Author
So whats the difference between jumping and flying ?
Flying produces an upwards force (lift) equal to the weight for horizontal flight.
The momentary increase in weight of the truck would be caused by the downward force as everyone jumped up, The Inertial energy required for you to 'spring up' in the air against the effect of gravity and your own weight, once you are actually up in the air for a second or two you are exerting no actual force on the lorry floor.
If you lifted yourself off the floor using some sort of 'jet pack' to hover using downward thrust, then you would have a similar effect as the pigeon wings

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