Question re. Brownian movement

[tranx]

I understand that e.g. pollen grains reflect the movement of the molecules in the e.g. water around them

 

Perhaps the induced movement of the pollen indicates that they have absorbed some energy and this generates some heat through friction, returning it to the system as the molecules lose heat to the pollen

 

This, like the rotation of planets, looks like 'perpetual motion', so may I ask what is really going on?

[danny8522003]

The motion of the pollen is due to water molecules colliding with them creating movement through conservation of momentum. These water molecules lose energy and give it to the pollen, and hence no energy is lost from the system.

 

The motion of the planets is not perpetual since energy is conserved. The rotation is due to the fact the matter the solar system is made of was rotating before it collapsed. The planets actually lose energy as they orbit the Sun but this is arbitrary and is not noticable.

[tranx]

Thanks, I think I get it now! I had interpreted 'perpetual motion' literally as movement that goes on and on, yet this is no problem according to the usual rules; I understand now because you explained that the energy, which was was there already, is just conserved

 

Re. "The planets actually lose energy as they orbit the Sun but this is arbitrary and is not noticeable" - this was interesting and I suppose the energy is conserved by being passed to other bodies

 

Appreciate the rapid advice

[danny8522003]

Actually the lost energy is thought to be given off as gravity waves or gravitons. Just as an electron would give off photons as it orbits a nucleus, and hence puts rest to the Bohr model.

 

It's interesting to see how energy is gained and lost but is inevitably conserved.

 

Glad I could be of help.

[J.C.MacSwell]

The motion of the pollen is due to water molecules colliding with them creating movement through conservation of momentum. These water molecules lose energy and give it to the pollen, and hence no energy is lost from the system.

 

The motion of the planets is not perpetual since energy is conserved. The rotation is due to the fact the matter the solar system is made of was rotating before it collapsed. The planets actually lose energy as they orbit the Sun but this is arbitrary and is not noticable.

 

Can you explain this? How is this arbitrary?

[danny8522003]

Sorry i meant negligible. It was late.. I was tired..