8-6) Weightlessness: (a) Suppose you are in an elevator that starts falling but
ID: 1370095 • Letter: 8
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8-6) Weightlessness: (a) Suppose you are in an elevator that starts falling but you don?t realize this is happening. During the first couple of seconds the elevator would be falling slowly enough that air friction is negligible, and you would feel weightless. even though you are not weightless. Explain why? (b) Astronauts riding in the International Space Station (ISS) orbiting the Earth appear to be weightless even though they are not outside of the range of the Earth?s gravitational force. Can you explain why? (c) Consider two astronauts in the SS who have masses of 52 kg and 70 kg. and are not moving with respect to the ISS. If they shove each other. and the more massive one moves away with a velocity of +13 m/s x, what is the direction and magnitude of the velocity of the other astronaut with respect to the coordinate frame of the ISS and the direction of motion of the first astronaut? A diagram would help!Explanation / Answer
(a) Any mass subjected to a force, should accelerate (Newton's law). We feel Earth's gravity but we do not accelerate. Because there is a force that pushes us the other way (the floor pushing back up against our feet). That is "weight".
If you are standing in an elevator and the cable breaks, the floor will no longer be pushing up against your feet, because the floor is accelerating (due to gravity) at the same rate as you. You would be weightless (until the elevator crashes in the basement)
(b) The gravity pulls the space station down and the station's sideways speed (orbital speed = 7.5 km/s = 16,800 mph) keeps it from hitting the ground. It is forever "falling" around Earth.
The astronauts inside are also attracted by Earth's gravity and they too are falling around. At the same rate. Therefore, there is nothing pushing against them (not the floor, not the walls, not the ceiling). No push back = no weight.
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