# Heat always flows away from a hot material to a cold material

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Heat always flows away from a hot material to a cold material
Heat Transfer What is a heat? Heat always flows away from a hot material to a cold material Remember, heat moves in predictable ways, from a high temperature to low temperature.

Hot objects in a cooler room will cool to room temperature.
Heat Transfer Hot objects in a cooler room will cool to room temperature. Cold objects in a warmer room will heat up to room temperature. So that everything is in a state of equilibrium, meaning equal.

Question If a cup of coffee and a red popsickle were left on the table in this room what would happen to them based on how heat moves? Why?

Question If a cup of coffee and a red popsickle were left on the table in this room what would happen to them based on how heat moves? Why? The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.

Heat transfers in three ways: Conduction Convection Radiation
Heat Transfer Methods Heat transfers in three ways: Conduction Convection Radiation

Conduction Conduction is heat energy moving from a high-temperature object to a low-temperature object. Occurs in solids only.

Conduction When you heat a metal strip at one end, the heat travels to the other end. Conduction is the direct transfer of heat or energy from one molecule to another molecule by collision.

In solids, every atom is bonded to another atom
In solids, every atom is bonded to another atom. If we apply heat to one part of a solid the atoms begin to vibrate.

The heated atoms vibrating causes atoms to collide.
Conduction The heated atoms vibrating causes atoms to collide. This passes the heat from one atom to the next. The energy spreads throughout all the molecules of the solid, and the temperature increases.

Conduction This is why when a metal pot or pan is placed on a hot stove, the whole pan becomes hot, rather than only the bottom.

Conduction examples

Conduction Lab If you have a metal skewer with blobs of butter on it and heat the rod, why will the blobs fall off one by one? How is this an example of conduction?

Convection Convection takes place when heated molecules move from one place to another, taking the heat with them. Convection is the primary way that heat moves through gases and liquids.

Convection

Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out, rise and become less dense.

Fluid movement Cooler liquids and gases s___.
ink Warmer liquids and gases r___ up. ise

Water movement Convection current Hot water rises Cooler water sinks

Convection Current The water or air at the bottom heats up first causing it to expand. Since the warmed air or water has a lower density (it’s lighter) than the air or water around it, it rises up. At the top, the air or water cools, increasing its density, which causes it to sink back down to the bottom. This up and down movement eventually heats everything. The continual cycling is called a convection current.

Explaining Convection
Convection currents cause the movement of magma within the earth.

Why is it windy at the seaside?

Where is the freezer compartment put in a fridge?
Cold air sinks Where is the freezer compartment put in a fridge? Freezer compartment It is warmer at the bottom, so this warmer air rises and a convection current is set up. It is put at the top, because cool air sinks, so it cools the food on the way down.

Radiation May Come From Other Sources
Have you ever sat too close to a campfire while cooking marshmallows? You’re enjoying the warmth ….. only to notice that your skin is really warm?

Radiation is the transfer of energy by electromagnetic waves
Radiation does NOT require matter to transfer thermal energy Radiation = heat escaping the sun So now we are going to cook with it!

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