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Transcript of Heat and heat technology
Heat and Heat Technology
Holt: Chapter 10
Fusion: Unit 4, Lessons 2-3
Temperature
• It is not simply “how hot or cold something is”
• Hot and cold are relative
• Temperature is, specifically, a measure of the average kinetic energy of the particles in an object
• All matter is made of particles that are constantly moving! (Remember the movements of solids, liquids and gasses)
• The more the particles are moving, the more kinetic energy, therefore, higher temperature
How do we measure temperature?
• Thermometers
• Thermometers can measure temperature due to thermal expansion.
• Thermal expansion is an increase in the size of a substance in response to an increase in the temperature of the substance.
• As a substance’s temperature increases, its particles move faster and spread out. There is more space between them = expansion.
The temperature scales
• You will have to know this
for your SOL test!
• 0K = absolute zero
• Absolute zero is the
temperature at which all
molecular motion stops.
Heat
• Heat is the energy transferred between objects that are different temperatures.
• When two things at different temperatures come into contact, energy is transferred from the object with the higher temperature to the object that has the lower temperature.
• The form of energy being transferred is thermal energy. Thermal energy is the total kinetic energy of the particles that make up a substance.
• More thermal energy = higher temperature
Quick check!
• Why do we use temperature instead of “hot” and “cold”?
• What are the three temperature scales?
• What is absolute zero?
3 ways to transfer thermal energy
• Conduction
•Convection
•Radiation
Conduction
• Thermal conduction is the transfer of thermal energy from one substance to another through direct contact.
• Substances that conduct thermal energy well are called thermal conductors.
• Substances that do not conduct thermal energy well are called thermal insulators.
Convection
• Convection is the transfer of thermal energy by the circulation or movement of a liquid or gas.
Radiation
• Radiation is the transfer of energy as electromagnetic waves.
Quick check!
• What are the three types of thermal energy transfer?
• What are some key words that can let you know that the type of transfer is conduction?
• Convection?
• Radiation?
Heat and Temperature Change
• Remember the concepts of insulators and conductors
• Different substances have different thermal conductivity
• Thermal conductivity is the rate at which a substance conducts thermal energy.
Specific Heat
• How easily does a material change temperature?
• Specific heat is the amount of energy needed to change the temperature of 1 kg of a substance 1 degree C. (p 285 Holt)
• The energy is measured in joules.
States of Matter
• Remember: states of matter are the physical forms of matter, which include solid, liquid and gas.
• A change of state is a change of a substance from one physical state to another.
• Is change of state a physical or chemical change?
Changes
• Heat can be involved in both physical changes (change of state) and chemical changes
• How do new bonds form in chemical reactions?
Food and Chemical Energy
• Where do we get energy?
• Energy that your body can use is released when chemical compounds such as carbohydrates are broken down. Energy is released in chemical reactions.
• You can find out how much chemical energy is in food by looking at the CALORIES on the nutrition label
• The calorie is the unit of energy in food = a measure of heat
• 1 calorie = 4184 J
Calorimeter
• A calorimeter is a device that measures heat.