january 22, 2015 agenda 1.roll 2.powerpoint titled: what is heat? 3.possible video: “basics of...
TRANSCRIPT
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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