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# astronaut help

## Question

Two astronauts are standing on a spinning space station shaped like a disk. They are the same radial distance away from the disk's center, and standing opposite to each other across from the center (e.g., if you draw a line connecting the two astronauts, the line crosses the disk's center.) One astronaut wants to toss a wrench to the other. Among the infinitude of trajectories which will accomplish this goal, characterize one of the trajectories without writing a single equation.

## 11 answers to this question

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Assuming there are no obstacles in the way (experimental equipment, life-support gadgets, etc), the first astronaut could just let go of the wrench without throwing and it should remain in the same position as both astronauts rotate into each other's position.

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It might cause injury, and take a great deal of strength to achieve,

but the trajectory of a rifle bullet would seem to work.

If the astronauts were of point size, the velocity would have to be infinite.

But assuming they are normal humans, rifle bullet speed should suffice.

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Assuming there are no obstacles in the way (experimental equipment, life-support gadgets, etc), the first astronaut could just let go of the wrench without throwing and it should remain in the same position as both astronauts rotate into each other's position.

If the thrower just lets go of the wrench, it will not stand still, but continue on a straight tangential course.

However, he could make it stand still by throwing it tangentially in the opposite direction at just the right speed.

Edit: It could then be "caught" by the other astronaut after a 1/2 revolution.

Edited by bonanova
Clarification

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Relatively the 2 Astronauts, the wrench and the disk are standing still with respect to each other. its just the background (stars,other space objects) that are revolving around them.. so just throw it straight.

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Relatively the 2 Astronauts, the wrench and the disk are standing still with respect to each other. its just the background (stars,other space objects) that are revolving around them.. so just throw it straight.

The astronauts are not in an inertial frame; the disk is spinning.

All objects (astronauts, wrench) that are "attached" to the disk are undergoing

a centripetal acceleration, and are following a curved, not straight, path.

Here's the difference.

All inertial frames are equivalent: there is no experiment to detect uniform velocity.

For example, you weigh the same in an up elevator as a down, or stationary elevator (except for starting and stopping.).

In a rotating frame, though, even if the rotation is constant, new forces appear.

For example, you can create artificial gravity that goes away when the spinning stops.

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Relatively the 2 Astronauts, the wrench and the disk are standing still with respect to each other. its just the background (stars,other space objects) that are revolving around them.. so just throw it straight.

The astronauts are not in an inertial frame; the disk is spinning.

All objects (astronauts, wrench) that are "attached" to the disk are undergoing

a centripetal acceleration, and are following a curved, not straight, path.

Here's the difference.

All inertial frames are equivalent: there is no experiment to detect uniform velocity.

For example, you weigh the same in an up elevator as a down, or stationary elevator (except for starting and stopping.).

In a rotating frame, though, even if the rotation is constant, new forces appear.

For example, you can create artificial gravity that goes away when the spinning stops.

the disk and all are spinning with respect to observer not co-moving with it.. and the astronaut are able to work and stand because as observed outside the disk rotation is uniform and not accelerating (inertial). Otherwise they would slip away from center if the rotation ,as observed from other reference frame,is slowly picking up speed as the jets fires.

In case of a hollow cylindrical structure they would be pushed within the wall away from the center in case of accelerated speed.

If the disk is accelerated up against their feet an artificial weight will be observe.

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Acceleration is a change in speed or direction.

The rotating disk is not an inertial frame.

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If the space station accelerates (increase speed in a direction) constantly
toward earth and fall (due to gravitation) on the North pole, an Observer
on earth (elf) would see the station not spinning .
The Astronauts would see the station not spinning.
While the observer in space see the station still spinning
and refer to it as not inertial.

What happen if the Astronaut drop the wrench?

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Go beside the other astronaut and toss ( if you really have to toss. )

Since we are not allowed to write equation I assume astronauts also can't precisely calculate tangents and whatnot.

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Possible slide it on the surface of the station?

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