What is heat?

What is heat? Whenever you hear the word heat, what usually comes to your mind? The hot sun, the fire that cooks your food, or a 95 degrees Fahrenheit during a hot summer?

Unfortunately, none of these situations above properly define heat.

Definition of heat:

Heat is the transfer of energy from one object to another as a result of a temperature difference between the objects.

Heat is heat transfer

The word transfer is key here in understanding what heat is.

Examples of heat transfer

  • You touch a hot piece of metal. Energy will enter your hand from the hot metal because the temperature of your hand was lower than the metal.
  • You dip your finger inside hot chocolate. Energy will enter your finger from the hot chocolate because the temperature of the hot chocolate is higher than the temperature of your finger. 
  • You boil water. Energy will enter the water from the hot burner.

This transfer of energy from something that is hot to another is what we call heat. In fact heat and heat transfer can be used interchangeably. 

Here is another example that may help you understand better. Your mom takes your temperature and you have a fever of 104 degrees.

Whenever you have a fever, the temperature of your body has risen.

Your body is hot. However, we never say that your body has heat in it. It is incorrect in physics to think that matter can contain heat.

However, it is OK to say that matter may contain energy and this energy may exist in several forms.

This energy could be kinetic energy, potential energy, electrical potential energy or heat.

While you struggle with your fever, what do you think will happen if you immerse yourself in water with a temperature of 65 degrees Fahrenheit?

The energy from your body will transfer to the water. This will as a result lower your body temperature.  This does not get rid of any infection your body may have, but it helps to keep your body temperature under control.

What is heat? Here is a better definition

You may have noticed so far that the transfer always happen from a warmer object to a cooler object. If you touch ice, why is your hand cold?

It is because the energy that existed in the form of heat in your hand transferred to the ice. 

Second definition of heat:

Heat is the transfer of energy from a warmer object to a cooler object.

The transfer of energy from the sun to the earth is heat.

The transfer of energy from the fire to your food is heat

A 95 degrees Fahrenheit during a hot summer is not heat. It is just the temperature during a hot summer. However, a transfer of energy from the hot summer to your body, making you feeling hot, is heat.

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