# B Can force be applied in vacuum?

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1. Aug 24, 2016

### donaldparida

Is the capability to apply force dependent on the medium.Suppose two human beings are placed in vacuum.Now, can they apply forces on each other?
Also, can force fields such as gravitational and electrical fields exist in vacuum and if so then why?

2. Aug 24, 2016

### Bystander

Yes. Yes. Yes. Think about it for a moment.

3. Aug 24, 2016

### A.T.

What else should happen? That they pass through each other like ghosts, or what?

4. Aug 24, 2016

### vanhees71

Well, I guess the two guys will die pretty soon in vacuo and thus not excert forces on each other anymore ;-)). SCNR.

5. Aug 24, 2016

### donaldparida

Then replace the humans with robots.

6. Aug 24, 2016

### rollete

7. Aug 24, 2016

I think you really mean to say in space - correct? Otherwise I have no idea why you think a vacuum affects forces. In space, you may be thinking there is nothing to "push against" - but how do rockets work, they expell a propellant in one direction that pushes ( generates a force) on the rocket in the opposite direction.

8. Aug 24, 2016

### A.T.

You do realize that we already sent humans and robots into space?

9. Aug 25, 2016

### vanhees71

Well, I don't understand the question. Why shouldn't you be able to exert a force on another object, only because you are in a vacuum in the first place?

10. Aug 25, 2016

### donaldparida

Well, I am confused over this since i used to think earlier that you apply force in vacuum but my physics teacher said that newtonian forces do not exist in vacuum.

11. Aug 25, 2016

### vanhees71

Did he give an explanation, how he came to that conclusion? It's totally ununderstandable to me, how you can get such an idea. The fundamental forces are all defined in "the vacuum". Forces like pressure of a gas or something like that are derived from the vacuum theory (hydrodynamics, kinetic gas theory) via statistical mechanics. On a fundamental level forces are mediated by fields, which can move through space as any other "object".

12. Aug 25, 2016

### donaldparida

No, he did not provide an explanation. Well the conversation between us was somewhat like this:
Me- What happens to the energy of an object when we lift an object in a vacuum or a fieldless region as opposed to the case when we lift it in a field such as a gravitational field(in which case its P.E. increases).
Teacher-Newtonian forces do not exist in vacuum and so the question of lifting them in vacuum does not arise.

13. Aug 25, 2016

### vanhees71

Well, if there is no gravitational force in a vacuum, how comes that the planets run in nice bound orbits around the sun? This is only possible if there is a force, according to Newton's 1st law. You teacher is thus plain wrong.

14. Aug 25, 2016

### A.T.

Maybe he meant the fieldless region not the vacuum as such?

15. Aug 25, 2016

### donaldparida

You mean that newtonian forces don't exist in fieldless regions

16. Aug 25, 2016

### ZapperZ

Staff Emeritus
When there is "no field", there is no force.

Your question to your teacher seemed to equate vacuum to fieldless region. They are not the same thing. You can have vacuum but with fields. This is VERY common. We accelerate charged particles in vacuum!

Zz.

17. Aug 25, 2016

### donaldparida

I guess you are talking about field forces and what about forces applied by contact.

18. Aug 25, 2016

### ZapperZ

Staff Emeritus
What do you think "contact" is at the miscroscopic level?

Zz.