What kind of energy do I possess when I exert a force?

[Brownian notions]

If I'm trapped between 2 walls, and I am pushing outwards such that I just balance the force, I am not doing work on the walls but I'm getting tired.

This is because chemical potential energy is converted into... kinetic energy (within muscles?) and heat energy right?

What if I replace the human with a battery powered robot?

1. What energy is the chemical potential energy of the batteries converted into?
2. How is it possible that the robot is exerting a force without "transferring" any energy?

Thanks!

 

[BvU]

converted into... kinetic energy (within muscles?) and heat energy right?

No kinetic energy in the steady state. Just heat.

Robot idem. Possible because battery power is dissipated into heat.

 

[PeroK]

If I'm trapped between 2 walls, and I am pushing outwards such that I just balance the force, I am not doing work on the walls but I'm getting tired.

This is because chemical potential energy is converted into... kinetic energy (within muscles?) and heat energy right?

What if I replace the human with a battery powered robot?

1. What energy is the chemical potential energy of the batteries converted into?
2. How is it possible that the robot is exerting a force without "transferring" any energy?

Thanks!

If you had a human bone handy, you could jam that between the walls and the force could be resisted indefinitely without an energy source.

The energy in your muscles is essentially used to keep your joints rigid.

 

[Brownian notions]

Thanks both of you.

Im a bit confused now:

the force could be resisted indefinitely

But this bone would be exerting force outwards right?
Am I right to say that there is no energy conversion going on here, but there is still a force being exerted outwards?

kinetic energy in the steady state. Just heat.

I've heard that some energy is converted to kinetic energy within muscles for contraction etc, because otherwise it seems like there would be a LOT of heat produced?

 

[PeroK]

Thanks both of you.

Im a bit confused now:But this bone would be exerting force outwards right?
Am I right to say that there is no energy conversion going on here, but there is still a force being exerted outwards?
?

There is no energy involved. Not in static equilibrium.

 

[CWatters]

A book on a shelf exerts a force on it without expending any energy.

Energy might be expended contracting muscle but after they have finished contracting they can continue to generate a force without suddenly getting a lot hotter.

 

[CWatters]

The basic equations are:

Work=force*displacement
Power=force*velocity

The walls aren't moving so you are doing no work on them. It might not feel like that but humans are not ideal machines. We consume a lot of energy even while asleep.

Humans are also rather bad measuring instruments... If you ride a bike up a hill twice, it can feel easy or hard depending on what gear the bike is in. This is true even if you ride up at the same speed both times so you are generating the same power.

 

[Dale]

Am I right to say that there is no energy conversion going on here, but there is still a force being exerted outwards?

Yes. A static force does not require energy. For energy to be transferred there must be a displacement in the direction of the force.

 

[person_random_normal]

What if I replace the human with a battery powered robot?

when the robot is trying to push the walls apart- the cement and other stuff is holding the structure together- so you can roughly say- the friction forces are acting as reaction forces(wherein action is force caused by the robot)
So, now for understanding the involved energy transfer - think about the molecular basis of friction - friction is resultant of lots and lots of minuscule electrostatic forces between any two surfaces. i.e shearing two contact surfaces will cause breaking and making of electrostatic bonds
Hence, finally, we can say - the chemical energy is being converted to electrostatic energy(very rough model)

 

[BvU]

No. Wall don't move $\Rightarrow$ no energy is converted.

 

[Brownian notions]

Thanks guys, i think i get it now. Really appreciate the help!

 

[person_random_normal]

No. Wall don't move $\Rightarrow$ no energy is converted.

Yes, the wall doesn't move, but there is some temporary deflection (few micro/nanometers) which we cannot notice!