# The Naked Scientists Forum

### Author Topic: Mechanical & Thermal Energy  (Read 8424 times)

#### sciencekid

• Jr. Member
• Posts: 11
##### Mechanical & Thermal Energy
« on: 19/01/2012 00:44:54 »
why are mechanical and thermal energy different. I know one is a system, and the other one is an object, but need help. Thnks.

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Re: Mechanical & Thermal Energy
« Reply #1 on: 19/01/2012 10:41:03 »
This is meant as a non-technical guide and I hope it helps to clarify matters. It's not meant to be a definitive answer.
One form of energy can be converted into another form of energy.  Energy is something that is consumed (or perhaps more correctly, diluted) when work is done.  Energy can neither be created (from nothing) nor destroyed.  Energy and mass are in a sense equivalent.  When work is done high grade energy (high temperature for instance) is converted into low grade energy (low temperature).  This often means that a small amount of something at a high temperature, as work is extracted, ends up as a large amount of something at a low temperature.  The same amount of energy is still there but in a more dilute form and therefore difficult to extract any more work from.  As energy is used (diluted) so entropy increases.  Entropy is a one way flow in any closed system.  The purest form of energy, if you like is heat that is photons.  Mechanical energy is a means of extracting either heat energy or stored energy (ultimately heat energy) in a spring or stored in a gravitational field etc.

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Re: Mechanical & Thermal Energy
« Reply #2 on: 19/01/2012 13:08:02 »
Energy is basically an accounting system, and is useful because if your system is closed and not leaking energy outside of itself, the total energy within it is constant.  This allows us to make useful predictions if we can somehow add up the energy in a system.

The problem is that some systems are more complex than others.  If a system is simple enough that you can calculate its energy using the laws of mechanics (by looking at the energy of each part individually and adding these energies up to get a total), then its called a mechanical system and its energy is mechanical energy.  If a system consists of many, many parts, then counting and adding is impractical.  In this case, various averaging techniques can be employed.  The system is called thermodynamic and its energy is thermal energy.  So the difference between the two types of energies has to do with the techniques used to account for them within a system, which in turn depends basically on whether you can count and add energies or you have to use averaging.

#### simplified

• Sr. Member
• Posts: 428
##### Re: Mechanical & Thermal Energy
« Reply #3 on: 19/01/2012 14:34:16 »
why are mechanical and thermal energy different. I know one is a system, and the other one is an object, but need help. Thnks.
Mechanical energy under power of electric charges is thermal energy.

#### JP

• Neilep Level Member
• Posts: 3366
• Thanked: 2 times
##### Re: Mechanical & Thermal Energy
« Reply #4 on: 19/01/2012 14:49:45 »
why are mechanical and thermal energy different. I know one is a system, and the other one is an object, but need help. Thnks.
Mechanical energy under power of electric charges is thermal energy.

Not true at all.  You can use electrical energy in a mechanical system and you can have thermal energy without electrical charges.

#### simplified

• Sr. Member
• Posts: 428
##### Re: Mechanical & Thermal Energy
« Reply #5 on: 19/01/2012 17:37:14 »
why are mechanical and thermal energy different. I know one is a system, and the other one is an object, but need help. Thnks.
Mechanical energy under power of electric charges is thermal energy.

Not true at all.  You can use electrical energy in a mechanical system and you can have thermal energy without electrical charges.
We don't discuss electrical energy here at all.Released thermal energy from power of electric charges is not thermal energy.Speed of wind is not temperature! ;)

#### MikeS

• Neilep Level Member
• Posts: 1044
##### Re: Mechanical & Thermal Energy
« Reply #6 on: 20/01/2012 08:49:30 »
JP

I suspect what simplified is getting at is if you trace the  the source of electrical energy back far enough then ultimately the source of the energy was thermal before it became mechanical, chemical etc.

I will probably regret saying that.
« Last Edit: 20/01/2012 08:54:45 by MikeS »

#### simplified

• Sr. Member
• Posts: 428
##### Re: Mechanical & Thermal Energy
« Reply #7 on: 20/01/2012 14:10:19 »
JP

I suspect what simplified is getting at is if you trace the  the source of electrical energy back far enough then ultimately the source of the energy was thermal before it became mechanical, chemical etc.

I will probably regret saying that.
I got that energy of electrons in atom is thermal energy.If an electron is free of attraction of electric charges then this electron has mechanical energy.
« Last Edit: 20/01/2012 14:11:59 by simplified »

#### syhprum

• Neilep Level Member
• Posts: 3813
• Thanked: 19 times
##### Re: Mechanical & Thermal Energy
« Reply #8 on: 20/01/2012 16:34:10 »
They are in fact not different The energy stored in a speeding bullet can easily be calculated i.e mass*velocity squared/2 in theory you could calculate the energy stored in a hot body by taking the sum of the kinetic energy stored in each speeding molecule but it is not very practical.

acknowledgement to JP who has allready stated this in even more detail.
« Last Edit: 22/01/2012 01:16:34 by syhprum »

#### simplified

• Sr. Member
• Posts: 428
##### Re: Mechanical & Thermal Energy
« Reply #9 on: 20/01/2012 17:03:41 »
They are in fact not different The energy stored in a speeding bullet can easily be calculated i.e mass*velocity squared/2 in theory you could calculate the energy stored in a hot body by taking the sum of the kinetic energy stored in each speeding molecule but it is no very practical.
8D Different energies make different things.High thermal energy of an air heats you.Kinematic energy of an air cools you.

#### simplified

• Sr. Member
• Posts: 428
##### Re: Mechanical & Thermal Energy
« Reply #10 on: 25/01/2012 13:26:15 »
I think free electron doesn't radiate photon,but moving  electron around positive field,losing energy, radiates photon. And so time of attraction by positive field shares electron and its energy. :)

#### The Naked Scientists Forum

##### Re: Mechanical & Thermal Energy
« Reply #10 on: 25/01/2012 13:26:15 »