# Conduction between two materials

1. Feb 10, 2013

### sgstudent

When I have a metal object at 0 degrees and a plastic object at 0 degrees, the metal feels colder as heat is conducted away at a faster rate. The reason for that would be that the metal is a better conductor of heat so when my hand touches it, it can start vibrating more quickly than the plastic.

So does this mean that how fast heat gets conducted into another material depends on the warmer material? For example if the metal and plastic is at 60 degrees, when I touch them they should feel the same? Because now that heat is transferred to the hands, the rate of heat flow into the hand from the hotter object will be the same (since the kinetic energy of the metal and plastic particles is the same so they should have the same rate of heat transfer to the hand). Is this correct?

Thanks

2. Feb 10, 2013

### Staff: Mentor

Nope. The metal would feel warmer and conduct heat into your hand at a greater rate.
Not only is the metal able to conduct heat into your hand better, it is also able to conduct heat within itself better too, so it also replaces the heat lost at the point of contact with your hand at a greater rate than the plastic can.

3. Feb 10, 2013

### Naty1

as, posted already, no; It depends on the temperature difference between materials and the conduction rate of the poorer conductor.

4. Feb 10, 2013

### sgstudent

Oh that's right! But if I were to touch it for a brief moment then they would feel the same? Or would the touch be too slow? Also what is the formula for this? Thanks

Last edited: Feb 10, 2013
5. Feb 11, 2013

### Staff: Mentor

That depends on how brief. If brief enough you wouldn't feel anything. A little longer and the metal would feel hot while the plastic probably wouldn't.

Sorry, I don't know that one.

6. Feb 11, 2013

### marcusl

Heat transfer is governed by a second order differential equation called the diffusion equation, and the key parameter governing the rate of transfer is the diffusivity. Wikipedia is a good starting point for this
http://en.wikipedia.org/wiki/Heat_equation
Heat transfer across the boundary between different media is a little more complicated. I can refer you to appropriate texts if you are interested.