Heat Transfer

That’s hot! Many things give off heat. Heat is sometimes very hot! All heat is energy. Sun fire electricity

What is thermal energy? Thermal energy is what we call energy that comes from heat. For example, a cup of hot tea has thermal energy in the form of kinetic energy from it’s particles. When you pour some milk into your tea, some of this energy is transferred to the particles in cold milk. What happens next? The cup of tea is cooler because it lost thermal energy to the milk.

How is thermal energy transferred? Thermal energy is transferred through a material by the collisions of atoms within the material. Over time, thermal energy tends to spread out through a material and equilibrium is established. –Equilibrium just means that both materials are at similar and unchanging temperatures

What is Temperature? Temperature is the measure of the average kinetic energy of the particles in a sample Basically, it is how fast the molecules in a substance are moving

3 Types of Thermal Heat Transfer Conduction Convection Radiation Think of an example of all three with your group

Conduction Transfer of heat from one material to another if they are in contact with one another. The two objects HAVE to be touching for conduction to occur Example: frying an egg, curling iron, hot plate

Convection Thermal energy can also be transferred by means of currents in air, water, or other fluids. The two objects are NOT touching when convection occurs. Think of when you feel heat from something but nothing is actually touching you Examples: convection oven, hair dryer, heat from a heater

Radiation Some thermal energy in all materials is transformed into light energy and radiated into the environment by electromagnetic waves. That light energy can be transformed back into thermal energy when the electromagnetic waves strike another material. Examples: heat from the sun, energy from the EM spectrum

Cooling A material tends to cool down unless some other form of energy is converted to thermal energy in the material. Most objects are always moving towards being cool

Campfire! Pretend you are at a campfire. You are roasting a hot dog on a metal wire coat hanger. Slowly the end of the hanger warms up, as it takes in the heat from the fire.

Ouch! If you leave the hanger in the fire for a long time, the whole hanger will become to hot to touch! Why does this happen?

Here’s the reason…. This happens even though the handle end was never placed into the flames. Heat moves from the flames to the metal handle. From there it moves to all the molecules in the hanger by conduction until it reached your fingers.

Heat on the move! Heat can move from one object to another, or from one molecule to another through the process of conduction.

What is a molecule? A molecule is like a tiny building block that makes up everything around us. We can’t see them with our eyes.

Hot All Over! As one molecule is heated it begins to move quickly. When it does it passes some of its heat energy to other molecules around it. When this happens, all the molecules of an object move heat from one to another, until they are all hot.

What things get hot fast? Some materials (objects) get warmer faster than others. Metal is a good conductor because it takes heat in quickly. Copper becomes hot quickly, so it is a conductor. Copper pots

You’re no good! Other things like wood, plastics, and cotton are not good conductors of heat energy. These are called insulators.

Color conductors! Some colors are good conductors of heat! Black, navy blue, and other dark colors take in heat quickly.

It’s getting hot in here! Have you ever noticed how quickly you get hot when you are wearing a black t-shirt on a summer day?

Cool colors?! Wearing white or light colored clothing outside helps you stay cool on hot days!

HONK! HONK! BEEP! BEEP! Question #3 Would a white car or black car on a summer day be hotter? Which do you think would be hotter to touch?

Which would you choose? Question #4 On a hot day, which side of the shirt would keep you cool?

Remember…. Heat moves through objects. This is called conduction!

Conductors Some things hold heat in faster than others. Metal and copper are conductors.

Insulators Plastic, wood, and cotton are insulators! They do not let heat in quickly! These things are insulators.

Stay cool dude! The color black takes in heat faster than cooler colors like white! On a hot day, wear a white shirt and chill out!