January 22, 2015

Agenda

1. Roll

2. PowerPoint Titled: What is Heat?

3. Possible Video: “Basics of Physics: Exploring Heat”

Subject Area: Heat

EQ: How is energy transferred using heat?

Questions:

1. What is heat?

2. What are the different methods of transferring heat?

What is Heat?

When you go to a check-up and the doctor places the metal stethoscope on your back and it feels cold. Why is this different than the tongue depressor which is the same temperature as the stethoscope? The difference is in the way the energy was transferred from the instrument to your skin.

Heat Is a Transfer of Energy

You might think of the word heat as being something hot. Heat also has to do with things that feel cold. The specific meaning of heat is: Heat is the transfer of energy between objects that are at different temperatures.

Partner Question:What is heat?Heat is …

When two objects at different temperatures come in contact, energy is always transferred from the object with the higher temperature to the object with the lower temperature.

Heat Is a Transfer of Energy

Heat and Thermal Energy

Thermal energy is the total kinetic energy of the particles that make up a substance.

Partner Question:What is Thermal Energy?Thermal Energy is …

Heat and Thermal Energy

When you hold an ice cube the thermal energy is transferred from your hand to the ice cube. The ice cubes thermal energy increases and the thermal energy in your hand decreases. The particles in your hand start moving slower and your hand feels cold!

Reaching the Same Temperature

When two objects at different temperatures meet, energy from the high-temperature object will be transferred to the low-temperature object until both objects reach the same temperature. This point is called thermal equilibrium. Thermal equilibrium is when two objects are the same temperature and no net change in either object occurs.

Conduction, Convection, and Radiation

There are three processes that involve a type of energy transfer, they are: Conduction, Convection, and Radiation.

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Conduction

Conduction is the transfer of thermal energy from one substance to another through direct contact.

Partner Question:What is Conduction?Conduction is …

ConductionAs substances come into contact, particles

collide, and thermal energy is transferred from the higher-temperature substance to the lower-temperature substance. Higher-kinetic-energy particles transfer kinetic energy to lower-kinetic-energy particles. Conduction makes some particles slow down and other particles speed up until all particles have the same average kinetic energy.

Conductors

Substances that conduct thermal energy well, are called conductors.

Insulators

Substances that do not conduct thermal energy well, are called insulators.

Convection

Convection is the transfer of energy by the movement of a liquid or gas.

Partner Question:What is Convection?Convection is …

ConvectionWhen you boil water the water will move in a

circular motion. The hot water will be less dense and will rise and the cooler water will be more dense and will fall. The circular motion of liquids or gases due to density differences that result from temperature differences is called a convection current.

Radiation

Radiation is the transfer of energy through matter or space as electromagnetic waves, such as infrared light or visible light.

Link

Partner Question:What is Radiation?Radiation is …

Greenhouse Effect

The greenhouse effect is the heating of the Earth due to radiation from the Sun that is trapped by the Earth’s atmosphere. If not for the greenhouse effect the Earth would be a cold lifeless planet.

Link

Heat and Temperature Change

On a hot day you might get into a car and touch the seat belt and the metal part is hot and the cloth part would not be as hot. Why is this?

Thermal Conductivity

Different substances have different thermal conductivities. Thermal conductivity is the rate at which a substance conducts thermal energy. The metal seat belt is more conductive to heat than the cloth. Even though they are the same temperature the metal will seem hotter because it will transfer the energy more rapidly to your hand than the cloth.

Specific Heat

Specific heat capacity is the amount of energy needed to change the temperature of 1kg of a substance by 1°C.

Link

Specific HeatIt requires less energy to

change the temperature of the metal buckle compared to the cloth even though they are the same size. Different substances will have different heat capacities.

Some common specific heats and heat capacities:

 Substance

 S (J/g 0C) C (J/0C)

for 100 g

 Air  1.01  101

 Aluminum

 0.902  90.2

 Copper  0.385  38.5

 Gold  0.129  12.9

 Iron  0.450  45.0

 Mercury  0.140  14.0

 NaCl  0.864  86.4

 Ice  2.03  203

 Water  4.179  41.79

     

Partner Question:

1. Why do substances get hotter faster than others?Some substances get hotter faster than others because …

Calculating Heat

The energy transfer between objects cannot be measured, it must be calculated. Heat can be expressed in Joules (j).

Calories and Kilocalories

Heat can be expressed in units called calories. A calorie is the amount of energy needed to change the temperature of 0.001 kg of water by 1°C. Therefore 1000 calories are required to change the temperature of 1kg of water 1°C. Calories are the units listed on food labels.

The Difference Between Temperature, Thermal Energy, and Heat

There are differences between temperature, heat, and thermal energy.

Heat Link

Temperature versus Thermal Energy

Temperature is the measure of the average kinetic energy of an objects particles and thermal energy is the total kinetic energy of an objects particles. A drop of boiling water had the same temperature as a pot of boiling water, but the pot has more thermal energy because there are more particles.

Thermal Energy Verses HeatHeat is the transfer of thermal energy. Objects

contain thermal energy, but they do not contain heat. Temperature Thermal Energy Heat

A measure of the average kinetic energy of the particles in a substance

The total kinetic energy of the particles in a substance

The transfer of energy between objects that are different temperatures

Expressed in degrees Fahrenheit, degrees Celsius, and Kelvin

Expressed in joules Amount of energy transferred in joules and calories

Does not vary with the mass of a substance

Varies with mass and temperature of a substance

Varies with mass, specific heat capacity, and temperature change of a substance

“Exploring Heat”What did you know?1. ________________________________2. ________________________________3. ________________________________What did you learn?1. ________________________________2. ________________________________3. ________________________________What do you want to know?1. _________________________________2. _________________________________3. _________________________________

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