Unit 7: Heat Transfer

Unit 7: Heat Transfer

I know…

• how to define conduction, convection, and radiation.

​​Learning Target

I can…

• describe how molecular motion relates to thermal energy.

Success Criteria

definition: the measure of the average kinetic energy in an object.

• particles within a substance are constantly moving (kinetic energy)

• as temperature increases, kinetic energy will also increase​

​​What is temperature?

• 3 units

  • Celsius (^oC)

  • Fahrenheit (^oF)​

    • American scale

    • rarely used in science​

  • Kelvin (K)​

    • 0 K is absolute zero = -273.13 ^oC​

Measuring Temperature

What type of energy is temp.?

Energy Transfer

• What type of energy is temp.?

  • temperature is energy transferred as heat (thermal energy)

  • energy must move for heat to occur​

• What is heat?

  • definition: the transfer of energy between the particles of 2 objects due to a difference in temperature​

Energy Transfer

• heat flows from high temperature to low temperature.

  • Question: what happens to your cold feet when you sit them in front of a heater?

How does heat flow?

• heat flows from high temperature to low temperature.

  • Answer: the warmth (heat energy) moves from the heater (high temp) to your cold feet (low temp)

How does heat flow?

There are 3 types of heat (thermal) energy transfers

1. Conduction

2. Convection

3. Radiation​

What is Conduction?

definition: heat (thermal) transfer of energy by direct contact

• the 2 objects in contact are at unequal temperatures.

• the heat will move from the warmer object to the colder object​

• Examples

  • holding a hot cup of hot chocolate with cold hands​, the heat from the cup will be transferred directly to your hands

  • ​ironing clothes, the iron is hot and by touching the clothes the heat is transferred directly to the clothing.

What is Convection?

definition: heat transfer of energy by the movement of a heated fluid/medium— this includes a liquid or a gas.

• heat transfer happens because there density changes as the fluid begins to warm.

• the phrase "hot air rises​" is correct because gases expand and rise as they heat up and become less dense than cold gas particles

What is Convection?

• Examples:

  • ​a space heater, it puts out warm air from the top and draws in cooler air at the bottom to heat up a room (air/gas is the medium)

  • boiling water, the cold water at the bottom gets warmer and rises because of the energy in the burner and then the cold water rushes down to replace it at the bottom.

What is Radiation?

definition: heat that gets transferred in rays/waves from one place to another WITHOUT any physical contact or a medium

• transfer of energy happens through electromagnetic waves (infrared, visible light, ultraviolet)​

• does NOT require the movement of matter

What is Radiation?

• Example

  • standing in sunlight​; radiation from the sun is a mixture of electromagnetic waves

    • most of the radiation is absorbed by the atmosphere, but people are exposed to the rest

Multiple Choice

Which of the following is an example of convection?

• sitting under a lamp at your desk

• a car engine getting hot after you turn the car on

• water boiling when cooking noodles on the stove

• your feet getting warm from the hot sand on the beach

Multiple Choice

The heat moving from a hot burner to a pot that is sitting on the stove is an example of which heat transfer?

• conduction

• absorption

• radiation

• convection

Multiple Choice

To keep the baby chickens warm a farmer uses heat lamps, this is an example of ______.

• conduction

• convection

• radiation

• isolation