# Specific heat capacity and heat capacity?

1. Sep 3, 2013

### threy

A spark does not cause injury when it strikes the skin of a child. If you touch the burning stem, it can cause severe burn on your fingers? WHY?

What's the difference between specific heat capacity and heat capacity?

2. Sep 3, 2013

### janhaa

The specific heat capacity is the heat required to change the temperature of a substance by a certain temperature interval.

The heat capacity of a substance is a measure of how well the substance stores heat. When heat supplies to a material, it will cause an increase in the material's temperature. The heat capacity is defined as the amount of heat required per unit increase in temperature.

http://en.wikipedia.org/wiki/Heat_capacity

3. Sep 3, 2013

### CWatters

If you are shot by a gun it's not the mass of the bullet that matters it's the energy it delivers when it hits you. Even a small object like a bullet can contain a lot of energy if it's travelling really fast.

"burning stem" = Bunsen burner stem?

So regarding the spark vs Bunsen burner stem...

What causes injury is not just the temperature of the object but the amount of energy it delivers to the person.

The amount of energy released by an object = The temperature change * The amount of stuff * A constant that depends on the material.

So when a metal spark hits you it might well cool from say 1000C to body temperature but because the amount of stuff (the amount of mass) is very low the energy it contains/delivers is also very low.

The Bunsen burner stem might not be as hot as the spark but it has much greater mass so it is able to deliver more energy to your body.

Regarding the constants...

Heat Capacity is the amount of energy (in Joules) stored in an object per degree temperature rise. It takes into account the mass of the object (eg the mass of the metal in the spark).

Specific Heat Capacity is the same as the Heat Capacity BUT it is calculated "per unit of mass". This makes it more useful because it allows you to calculate the amount of energy in any size lump of metal simply by multiplying by the mass of metal.

So in short one takes into account the mass and the other doesn't.

Last edited: Sep 3, 2013
4. Sep 3, 2013

### CWatters

ps There are other versions of the Specific Heat Capacity. In some situations it might help to know the "volumetric specific heat capacity" which is the amount of energy per degree per unit volume of the material. To calculate the energy stored you would multiply by the volume rather than the mass.