Introduction: Temperature = a measure of the AVERAGE kinetic energy in a substance. Heat energy is measure in Joules
Expansion Def: When objects are heated up and their temperature increases, they will normally expand. ◦ The molecules move farther apart.
Contraction Def: When objects cool down they will normally contract. ◦ The molecules come closer together.
Absolute Zero: 0K or -273 ˚C ◦ All molecular motion stops ◦ Is only a theory ◦ The basis for the Kelvin scale
Temperature Scales: Kelvin ◦ 0 K is the lowest temp possible This is absolute zero Fahrenheit ◦ Freezing point of water 32 ◦ F, and the boiling point is 212◦F. Celsius ◦ Freezing point of water is 0 ◦C, and the boiling point is 100◦C. ◦ Scientists use the Celsius scale
Converting Fahrenheit to Celsius To convert temp from ◦ F to ◦ C: ◦ C= (5/9) ( ◦ F-32) To convert temp from ◦ C to ◦ F: ◦ F= (9/5) ( ◦ C ) + 32 To convert temp from ◦ C to K: K = ◦ C + 273
Example: To convert 68 ◦F to ◦C, first subtract 32, multiply by 5 and then divide by 9. The result is 20 ◦C. *Remember: ◦ C= (5/9) ( ◦ F-32) ◦ C= (5/9) (68 ◦ F-32) ◦ C= (5/9) (36) ◦ C=180/9 ◦ C= 20
Heat: Def: The transfer of energy between objects that are at different temperatures; Energy is always transferred from higher- temperature to lower-temperature objects, until thermal equilibrium is reached.
3 Types of Heat Transfer: Conduction Convection Radiation
Heat Transfer #1: Conduction = transfer of heat by direct contact (molecule to molecule) ◦ Ex- metal spoon in a hot bowl of soup ◦ Conductors- conduct thermal energy very well Ex- Iron, steel, gold ◦ Insulators- Do NOT conduct thermal energy well Ex – rubber, plastic, wood
Heat Transfer #2: Convection = Transfer of energy by convection currents in liquids and gases Warmer fluids are less dense than colder fluids, thus warm fluids rise and cold fluids fall. ◦ fluid = anything that flows (liquids & gases) ◦ not possible in solids ◦ hot air balloons, “convection” ovens
Example: The water at the bottom of a pot on a stove burner gets hot because of contact with the pot itself (conduction). As a result, the hot water becomes less dense because its higher-energy particles have spread apart. As the warm molecules rise to the top of the pot the cooler molecules sink back down into the pot. This circular motion creates a convection current.
Heat Transfer #3: Radiation = transfer of heat by electromagnetic waves ◦ Wavelengths can be; infrared, ultraviolet, and visible light. ◦ Only type of transfer that can occur through empty space. Sun Earth
Example: The coils of an open heater warm a room by radiating visible light and infrared waves.
Thermal Energy: Def: The total energy is equal to the particles that make up a substance. An object at a high temperature has more thermal energy than the same object at a lower temperature. The more moving particles that you have, the greater the thermal energy!!
Example: When you hold an ice cube in your hand, thermal energy is transferred from your hand to the ice cube. The ice cube’s thermal energy will increase and your hand’s thermal energy will decrease!! ◦ THIS MAKES YOUR HANDS FEEL COLD!!
Thermal Conductivity: Def: The amount of energy at which a substance conducts thermal energy.
Specific Heat Capacity: Def: The amount of energy needed to change the temperature of a 1kg object by 1˚C.
The law of conservation of energy: States that; energy cannot be created or destroyed.
Review: What are the 3 types of temperature scales? Kelvin, Fahrenheit, and Celsius
Review: List the three types of thermal energy transfer and give an example of each. Conduction- molecules have to be touching!! Convection- thermal heat currents Radiation- travels is waves
Review: What is the difference between heat and temperature? Temperature = a measure of the AVERAGE kinetic energy in a substance. Heat=The transfer of energy between objects that are at different temperatures.
Review: What is absolute zero? 0K or -273 ˚C ◦ All molecular motion stops ◦ Is only a theory ◦ The basis for the Kelvin scale
Review: If it is 62 ◦F outside today, what would the temperature be in ◦C? ◦ 16.66 ◦C What would it be in K? ◦ 289.66 K