Temperature, Heat & Expansion

Temperature - The quantity that tells how hot or cold something is compared with a standard. Temperature - The quantity that tells how hot or cold something is compared with a standard. Measuring temperature: Measuring temperature: A common thermometer measures temperature by showing the expansion & contraction of a liquid in a glass tube using a scale. *the liquid is usually mercury or colored alcohol *the liquid is usually mercury or colored alcohol

Temperature Scales Celsius Celsius - most widely used scale - international scale c = temperature at which water freezes c = temperature at which water boils Fahrenheit Fahrenheit - used commonly in the U.S o = temperature at which water freezes o = temperature at which water boils Kelvin Kelvin - used in scientific research - degrees are the same as Celsius and are called “Kelvin” - 0 o K = absolute zero (0 o K = -273 o C) **Absolute zero is the temperature at which a substance has NO kinetic energy.

Temperature is proportional to the average kinetic energy. Temperature is proportional to the average kinetic energy. As temperature increases – kinetic energy increases. As temperature increases – kinetic energy increases.

Heat Heat – the energy that transfers from one object to another because of a temperature difference. Heat – the energy that transfers from one object to another because of a temperature difference. **HEAT IS ENERGY**  Heat is energy “in transit” from a body of higher temperature to one of lower temperature  The energy resulting from heat flow in Thermal energy.

Thermal Equilibrium What is thermal equilibrium??? When objects in thermal contact with each other reach the same temperature and no heat flows between them. When objects in thermal contact with each other reach the same temperature and no heat flows between them. ex: to read a thermometer we wait until the liquid stops moving. This is the point when the liquid in the thermometer and the substance being measured have reached thermal equilibrium.

Internal Energy The grand total of all energies in a substance is the internal energy. A substance does not contain HEAT, it contains ENERGY !!! This includes: The KE of moving molecules and atoms of a substance. The PE due to the forces between molecules or atoms.

Measuring Heat  Heat is measured in calories.  A calorie = the amount of heat required to raise the temp. of 1g water, 1 o C. A kilocalorie = 1000 calories A kilocalorie = 1000 calories  Kilocalories are the heat unit used in rating foods. Kilocalories are often referred to as Calories. (with a capitol “C”)

Specific Heat Capacity  Specific heat is the quantity of heat required to raise the temp. of a unit of mass of a substance by 1 degree.  Different substances have different capacities for storing internal energy (re: ability to “hold heat”) (re: ability to “hold heat”)and require specific quantities of heat to raise the temp. of a given mass a specific number of degrees.

Example: 1g of water requires 1 calorie to raise the temp. 1 o C. 1g of water requires 1 calorie to raise the temp. 1 o C.WHILE 1g of iron requires 1/8 as much energy to raise the temp. 1 o C. 1g of iron requires 1/8 as much energy to raise the temp. 1 o C. Water absorbs more heat per gram that iron for the same temperature change. So… water has a higher Specific Heat. (BTW – water is considered to have a very high sp.heat)

Thermal Expansion When the temp. of a substance increases the molecules move faster (increase KE) This results in the EXPANSION of the substance. With few exceptions – all forms of matter (solid, liquid & gas) expand when heated and and contract when cooled.

Heat Transfer

Conduction Conduction = heat transfer within and between different materials in direct contact. (molecule to molecule) Conduction = heat transfer within and between different materials in direct contact. (molecule to molecule) conductor – material that conducts heat well (metal) insulator – material that delays the transfer of heat (wood)

Poor conductors = good insulators Poor conductors = good insulators Good conductors = poor insulators Good conductors = poor insulators Which feels colder: barefeet on tile or carpet? The tile – because it is a good insulator. The heat moves from your feet to the tile. Does a blanket make you feel warmer? The blanket is a good insulator and delays the transfer of heat from your body to the air.

Convection Convection is when heat is transfer through a current in a fluid. Convection is when heat is transfer through a current in a fluid. ** fluids can be either liquids or gases ** fluids can be either liquids or gasesexamples: - Air in contact with a hot stove rises and warms the region above. - Water boils through convection - convection currents stir our atmosphere

Radiation Radiation is the transfer of heat through electromagnetic waves. (UV light, visible light, infrared, microwaves, radio waves, etc.) Radiation is the transfer of heat through electromagnetic waves. (UV light, visible light, infrared, microwaves, radio waves, etc.)Examples: - The sun - a lightbulb - a fireplace Any energy, including heat, that is transmitted by radiation is called radiant energy.