Heat Transfer Radiation Conduction Conduction Convection Convection

The speed of a material's molecules or atoms determines its heat energy. The speed of a material's molecules or atoms determines its heat energy. Heat is the total kinetic energy of an object. Heat is the total kinetic energy of an object. So, when you record the temperature of a substance you are recording the SPEED of the molecules or atoms. So, when you record the temperature of a substance you are recording the SPEED of the molecules or atoms.

Radiation The transfer of energy through electromagnetic waves. The transfer of energy through electromagnetic waves. Does not need a medium (solid, or gas) in order to move. It travels through empty space. Does not need a medium (solid, or gas) in order to move. It travels through empty space.

Conduction Heat energy can be transferred from one substance to another when they are in direct contact. Heat energy can be transferred from one substance to another when they are in direct contact. EXAMPLE: frying an egg….the pan (solid) heats the egg. EXAMPLE: frying an egg….the pan (solid) heats the egg.

Since the atoms are closer together, solids conduct heat better than liquids or gasses. Since the atoms are closer together, solids conduct heat better than liquids or gasses. Heat spreads by conduction when atoms increase their vibrations, and pass this energy on to those nearby. Heat spreads by conduction when atoms increase their vibrations, and pass this energy on to those nearby.

Convection Heat transfer in fluids (liquids and gases). Heat transfer in fluids (liquids and gases). Molecules of the fluid must come in contact with one another. Molecules of the fluid must come in contact with one another. Image: As the warmer air rises (less dense), it passes its energy to other air molecules. When it moves away from the heat source it gets cooler (more dense) and sinks. CONVECTION CURRENT! Image: As the warmer air rises (less dense), it passes its energy to other air molecules. When it moves away from the heat source it gets cooler (more dense) and sinks. CONVECTION CURRENT!

The Lab You will be working with hot water..so you must wear safety goggles. You will be working with hot water..so you must wear safety goggles. I will explain how you are to conduct the lab. So please pay attention! I will explain how you are to conduct the lab. So please pay attention! Pay close attention to what happens when you place the cold color dye and what happens to the warm color dye. Remember……..always consider the placement of the molecules! Pay close attention to what happens when you place the cold color dye and what happens to the warm color dye. Remember……..always consider the placement of the molecules!

The lab What occurred when your group placed the food color representing the “cold water” into the tray? What occurred when your group placed the food color representing the “cold water” into the tray? What you should have observed was the food coloring “resting” on the bottom of the tray. What you should have observed was the food coloring “resting” on the bottom of the tray.

WHY? WHY? The cold water molecules are more dense, which means they are closer together. Since they are more dense they have less energy and are moving less. The cold water molecules are more dense, which means they are closer together. Since they are more dense they have less energy and are moving less.

When your group placed the food coloring that represented the warm water into the tray over the heat source, the food coloring started to rise and spread. When your group placed the food coloring that represented the warm water into the tray over the heat source, the food coloring started to rise and spread. WHY? WHY? The warm water molecules were less dense and contained energy that was transferred by the bottom of the tray (conduction). The warm water molecules were less dense and contained energy that was transferred by the bottom of the tray (conduction).

As those molecules start to rise they pass the energy to other water molecules by the process of convection. As those molecules start to rise they pass the energy to other water molecules by the process of convection. As the warm water rises, it is moving away from the heat source and starts to cool. However, warmer water is still rising below the cooling water. This causes the cooler rising water to be pushed out of the way. As the warm water rises, it is moving away from the heat source and starts to cool. However, warmer water is still rising below the cooling water. This causes the cooler rising water to be pushed out of the way.

What happened when your group placed food coloring representing the cold water closer to the heat source? What happened when your group placed food coloring representing the cold water closer to the heat source? The food coloring was moving towards the heat source. The food coloring was moving towards the heat source. WHY? WHY?

Same concept from the “crushing the can lab”. Warm water rising is less dense that creates “more space” for the more dense cold water to fill. Same concept from the “crushing the can lab”. Warm water rising is less dense that creates “more space” for the more dense cold water to fill. Warm = Low pressure Warm = Low pressure Cold = High pressure Cold = High pressure