Projectile

[howelli]

Is it actually possible for someone to fire a projectile on Earth and around it such that it's trajectory and velocity enables it to hit the back of that same persons head if remaining stationary. If so how?

[GOONBIRD]

this remind me of a discussion which we had, when i worked in the space industry in america many years ago. would it be feasable to have banks of rockets to spin the earth, so that an i.c.b.m. would land on the launching site? i think we decided that the logistics were insurmountable and the consequent devestation it would cause to the rest of the planet was not justified!

[brachiopod]

You are effectively asking if it is possible to put a projectile into a low altitude orbit.

The short answer is no, unless the projectile was self powered to overcome air resistance.

A satellite orbiting the Earth with a velocity of X really wants to travel in a straight line and shoot off into space (a bit like twirling a weight on a string around your head and letting go of the string).
The Earth's gravity wants to pull the satellite crashing back to Earth.
With the right velocity, these forces will balance and the satellite remains in a stable orbit.
Since the force exerted by gravity varies with distance (altitude), there is specific velocity required for each altitude.

At low altitudes, the Earth's atmosphere would slow the projectile, causing it to crash to the ground. Even without air resistance, the velocity required would be very high too (though I can't be bothered to work it out at this time on a Saturday morning !)

It would perhaps be possible on the Moon, which doesn't have an atmosphere - anyone care to calculate the velocity required?

[howelli]

I thought it so. Thanks.

[landie]

Never heard of a Boomerang?

[bernardo]

A boo!-meringue would follow an elliptical path and come back to the p[lace from which it was launched, i.e. near the hand, not the back of the head.

[brachiopod]

Wa-hay, bernardo ! long time, no....see/hear/type etc

[john91]

its not quite the same, but I did read that if you could stand on a planet with a sufficiently high  force of gravity you would be able to see the back of your head as the light waves would be bent around the planets surface.