Heat Transfer

 

Heat is transferred from one object to another in three different ways.

- Conduction

- Convection

- Radiation

 

      1) Conduction -- This is the transfer of heat that occurs when a warmer particle collides with a cooler particle and transfers energy ( heat). The two substances are in contact with each other. This type of heat transfer usually occurs in solids.

 

- The particles in the hotter object are vibrating faster and when they hit the particles in the cooler object they pass on the kinetic energy( their heat). The particles do not move around. For example: A pan on the stove.

 

      2) Convection-- This is the process where heat is transferred when a liquid or gas moves from one place to another carrying heat with it.

 

-- Warm water or air rises and when it cools it falls back down creating convection currents. These convection currents are what transfers the heat. Some examples of convection currents are:

- wind is a type of convection current

 

- continental drift ( the movement of continents around the Earth) are caused by convection currents in the Earth.
 

 

  3) Radiation -This is a type of heat transfer where the heat is transmitted by waves.The waves are Electromagnetic Waves. Some examples of these type of waves are:

      - radio waves

      - microwaves

      - light

      - x-rays

 

Conductors/Insulators

 

 

   We know that heat can be transferred or move through an object. The rate that an object conducts heat is called it's Thermal Conductivity.

 

   Some substances have higher conductivity then others which means they conduct heat better. Metals are good conductors of heat, which is why they are used in things like cookware and radiators.

 

   Things that are poor conductors of heat are called Insulators.For example the handles of cookware are plastic or wood because they are poor conductors and stay cool when the rest of the pan heats up.

 

We use materials that are good insulators in our homes to prevent the transfer of heat. These insulators keep heat in, in the winter and out in the summer. They reduce the transfer of heat. For example: Fiberglass insulation( pink) is used in houses.

 

   Thermos bottles use a vacuum as an insulator. The vacuum is completely empty, there are no particles, so therefor conduction and convection cannot occur.

 

 

Temperature/Heat

 

What is the difference between temperature and heat?

      Heat is also known as Thermal Energy. Heat can be defined as the total kinetic energy of a substance. Heat is measured in Joules.

      Temperature can be defined as the average kinetic energy of a substance. It is measured in degrees Celsius.

This means that the amount of a substance does not affect temperature but it does affect heat.

 

Specific Heat Capacity

 

Another idea when talking about heat is called specific heat capacity. This is defined as the amount of heat needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.

Some heat capacities of some common substances are:

                                            water 4.18

                             alcohol 2.43

                             soil 0.80

                             steel 0.42

                             wood 1.71

 

What these numbers mean is the larger the heat capacity              ( number) the most heat that is required to raise the temperature.
In other words a substance with a large heat capacity is more resistant to getting its temperature changed.