Gravity?

[Gareth56]

If gravity has infinite range why do you feel weightless if you're traveling through space at constant speed? For example if I were traveling (in a space craft) at constant speed towards the Moon why would I feel weightless?

[DrP]

The gravitational effect of an object on another body decreases with distance. It's an inverse square relationship - so at distances past a certain threshold the effect is negligable and you feel weightless.

 

Force = G.m1.m2 / 4.pi.epsilon0.r^2 (sorry - will sort it out with LaTeX LaTeR oN - in a hurry:-))

[D H]

If gravity has infinite range why do you feel weightless if you're traveling through space at constant speed? For example if I were traveling (in a space craft) at constant speed towards the Moon why would I feel weightless?

If you were traveling at a constant speed toward the Moon you would not feel weightless. The spacecraft would have to be thrusting continuously to maintain a constant speed. You would however feel weightless if the spacecraft was in free drift.

 

Wile the International Space Station has to reboost occasionally to overcome the slow loss of altitude due to atmosphere friction, it is in free drift most of the time. During these periods of free drift the astronauts on the Station feel weightless. Yet a quick calculation shows that the gravitational force is only reduced by about 10%.

 

So why don't the astronauts on the Space Station feel like they weigh 90% of what they weigh on the Earth's surface? The answer: You do not feel gravity. You cannot even measure (directly) the force due to gravity.

[Sisyphus]

And the reason you don't feel gravity is because it acts on all parts of you equally (well, in direct proportion to those parts' inertia), so there is no internal tension or compression. That is, unless the strength of the gravitational field is significantly different from one end of you to the other, in which case you'll have a "tide." But unless you're the size of a planet or right next to a black hole, that's not going to happen.

[Gareth56]

The reason I asked the question was I read the following quote on:-

 

Weightlessness

 

"The condition of zero-gravity (zero-g) or microgravity experienced by all spacecraft and their occupants when in orbit, in any other state of free fall, or traveling through space at constant speed."

[D H]

Garethm you're reference is a free on-line encyclopedia that doesn't support editing (that I can see). The underlined phrase is misleading at best (a nice way of saying "wrong"). Better written the phrase should be, "... or traveling through deep space (far from any massive body) at constant speed". Wikipedia and hyperphysics have much better descriptions of "weightlessness". See http://en.wikipedia.org/wiki/Weightlessness and http://hyperphysics.phy-astr.gsu.edu/Hbase/mass.html#wtls.

[Gareth56]

I'm obliged. I thought I'd check with the experts before taking what I read at face value.