Gravity

[Pieslewis]

I'm not sure if this is the right forum but here goes.

We are told that the moon's orbit is maintained by Earth's gravity i.e. the Earth's gravitational pull is strong enough to prevent the moon escaping into space.

Why then do we see astronauts and space objects float when in very close proximity to Earth? Also photos from Apollo 13 show the condensed moisture running down/across the windows however at the same time spacecraft objects e.g. manuals, duct tape pens etc all seem to float. There would appear there is something wrong with this.

[M40]

It's all about mass and mutual attraction. 

Interestingly, I did read something recently, can't remember where, it said that the moon was far closer to us more than a couple of years ago and is moving away from us at about 1cm a year. 

[vlaiv]

23 minutes ago, Pieslewis said:

Why then do we see astronauts and space objects float when in very close proximity to Earth?

Because things in "free fall" don't experience gravity.

This is true close here on earth's surface and in orbit.

When you start to fall - you feel weightless - same feeling you get when for example elevator starts moving downwards while you are in it.

Free fall does not need to be directed downward - it can be directed sideways - body orbiting another body is in effective "free fall".

You can see this if you imagine cannon shooting projectiles with ever increasing speed:

Cannonball falls to the ground each time - until you reach certain speed - where it is perpetually falling and "missing" the earth. If you shoot it faster than that - it will fly away into infinity (that is called V1 - or first cosmic velocity, speed that puts thing into an orbit).

Astronauts in space together with ISS or space shuttle are in orbit, so they are in free fall and don't experience gravity pull.

23 minutes ago, Pieslewis said:

Also photos from Apollo 13 show the condensed moisture running down/across the windows however at the same time spacecraft objects e.g. manuals, duct tape pens etc all seem to float. There would appear there is something wrong with this.

As for moisture on window - well it condenses there into drops - but these drops behave the same as far as gravity goes, however - gravity is not the only thing acting on bodies.

Any sort of accelerated motion will cause those drops to slide across the glass and create trails. It can be space craft accelerating / decelerating or simply rotating (centrifugal force).

There are other forces that can move water as well - like capillary force and surface tension.

 

Edited October 25, 2022 by vlaiv