Lesson 2 Summary - Thermal Energy Transfers

Radiation is heating by LOCATION.

1. With radiation, you don’t need to be touching a hot object to be warmed by it.  (Ex:  We don’t put our hands into a fire to warm them by a fire)

2. Radiation is the way heat gets from the Sun to the Earth because space is a vacuum (it’s completely empty).

3. Radiation can transfer heat through a solid, a liquid, or a gas.

Conduction is heating by TOUCH or DIRECT PHYSICAL CONTACT.

1. With conduction, a hotter object is physically touching a colder object.  The hotter object will donate thermal energy until the two objects have the same temperature.

2. With conduction, the colder object does not send its particles into the hotter object, but simply accepts energy from the particles in the hotter object.

3. A material through which thermal energy flows easily is known as a thermal conductor.  Metals make good conductors.

4. A material through which thermal energy doesn’t flow easily is known as a thermal insulator.  Cloth, cotton, wood, foam, and air are examples of good insulators.

5. The specific heat of a material tells you how much heat is needed to raise the temperature of that material.

   1. Objects with a LOW specific heat are good conductors- you don’t need to give them much heat in order to warm them up.

   2. Objects with a HIGH specific heat are good insulators- you have to give them lots of heat in order to warm them up.

   3. WATER has an especially high specific heat.  It takes a great deal of energy to raise the temperature of water.   This is why pools, lakes, and oceans stay cool during the summer, even when it’s very hot outside.

3. Convection  is heating by MIXING.

   1. Convection only occurs in liquids and gases.

   2. With convection currents, a fluid that is heated expands and rises.  As it does so, it’s replaced by denser molecules of the same material that are cooler.  These molecules, in turn, get warmer, expand, and rise.  They are once again replaced by cooler molecules of the same material.

   3. Convection currents circulate the air in a room, the water in Earth’s oceans, and cause winds and breezes to blow.

Materials expand when they are heated, and contract, or shrink, when they are cooled.  

This happens because as molecules in a substance are heated, they gain kinetic energy (move faster), spreading out in the process.

Similarly, when molecules in a substance lose heat, they also lose kinetic energy (slowing down), making them get closer together.

Thermal expansion is any increase in a material’s volume when its temperature increases.

Thermal contraction is any decrease in a material’s volume when its temperature decreases.

Thermal expansion and contraction are most noticeable in gases and less noticeable in liquids.  They are the least noticeable in solids.