# Naked Science Forum

## General Science => General Science => Topic started by: mrsmith2211 on 27/10/2016 01:34:54

Title: Would a water droplet retain its round shape in microgravity?
Post by: mrsmith2211 on 27/10/2016 01:34:54
So my late night thoughts started with a water balloon. If the water balloon was spinning really fast and hit the ground I would think the water progresses due to inertia in a straight line path to the ground.

Now I have seen videos of guys in outer space under low g situations able to play with a water blob due to surface tension like a ping pong ball.

My guess a water blob would hold it's circular shape in 0 g in spite of spin.

so this would men centrifugal or centripetal forces do not apply in 0 gravity.

Does that mean a Centrifuge does not work in 0 G? Or if you had a centrifuge in low g and suddenly stopped it would the heavier elements end up on the side instead of the bottom?

Which leads me to a bigger question, why are we drawn towards the center of the earth rather than being spun off the earth?

Title: Re: Water gravity centripudal centrifugal confusion
Post by: Colin2B on 27/10/2016 04:05:16
So my late night thoughts started with a water balloon. If the water balloon was spinning really fast and hit the ground I would think the water progresses due to inertia in a straight line path to the ground.
If you are thinking that the balloon would burst and release the water then individual droplets e.g. at the circumference, would travel tangentially and then being pulled down by gravity (an acceleration) would follow a curve to the ground.

My guess a water blob would hold it's circular shape in 0 g in spite of spin.
Circular yes, spherical no.

so this would men centrifugal or centripetal forces do not apply in 0 gravity.
Not true

Does that mean a Centrifuge does not work in 0 G? Or if you had a centrifuge in low g and suddenly stopped it would the heavier elements end up on the side instead of the bottom?
A centrifuge should work normally in space - unless the motor has failed!

Which leads me to a bigger question, why are we drawn towards the center of the earth rather than being spun off the earth?
Err ..... gravity?
Title: Re: Water gravity centripudal centrifugal confusion
Post by: jerrygg38 on 29/10/2016 14:21:25
Which leads me to a bigger question, why are we drawn towards the center of the earth rather than being spun off the earth?
If the Earth was spinning at a huge velocity we would be flying off.
So the force of gravity mg = m 32ft/sec/sec. is much less than
mV^2/R
V= 24,000miles/24 hours =1000 miles /hour = 0.277 miles per second
This equals 52.46E-6 ft per second. then we square this and divide by the radius of the Earth of approx 3000 miles = 15.84E6 ft
Thus the centrifugal acceleration  is 1.5E-17 verses 32 for gravity.
So unless I have a calculation error, the force to spin us of the Earth is so tiny that it is meaningless.
Title: Re: Water gravity centripudal centrifugal confusion
Post by: evan_au on 29/10/2016 22:50:43
Quote
Does that mean a Centrifuge does not work in 0 G?
I hope not!
That would mean that 2001 Space Odyssey and The Martian made an error in their science (apart from the huge, glaring ones!).

But seriously, spacecraft designers are concerned about the effects of microgravity on human skeleton and muscles during a mission to Mars (for example), where the explorers would need to stand on their own two feet once they arrived there, without extensive medical staff to help them.

One of the possible approaches is a spinning spacecraft - perhaps two capsules, spinning on opposite ends of a tether?
Title: Re: Water gravity centripudal centrifugal confusion
Post by: Colin2B on 30/10/2016 00:04:45
....perhaps two capsules, spinning on opposite ends of a tether?
I'm told that's a load of bolas
Title: Re: Water gravity centripudal centrifugal confusion
Post by: jerrygg38 on 30/10/2016 14:35:34
The simple solution is for the spacecraft to have a constant acceleration for half the trip and a constant deceleration for the last part of the trip. Of course this would require advanced engine design would could take two partially radioactive ingredients into an atomic furnace plus the proper electromagnetic and photonic fields to produce photonic emissions. That is for the future however.