Thermal Energy-Total Energy All matter is composed of atoms and molecules Atoms & Molecules are constantly in motion The motion is “kinetic energy” Water with low kinetic energy is ice Water with more kinetic energy is liquid With a high amount of kinetic energy is steam (vapor)

Thermal Energy Potential energy-stored energy Kinetic energy-energy of motion Thermal energy of a substance is the sum of all the potential and kinetic energy of the particles of a substance as they move around. When you pump up a bicycle tire, the temp of the air in the tire goes up. Why? When you use propane to provide fuel to a camp stove, the can gets cold. Why?

Temperature Temperature is based on an arbitrary scale. In the US, we like to use 32 for freezing and 212 for boiling (water in Fahrrenheit) Other places like to use 0 and 100 for freezing and boiling. Converting: C= 5/9(F-32) F=9/5C+32 Temperature gives us a measure of the average kinetic energy of something, for purposes of comparing

Temperature Conversions Convert the following Celsius temps to Fahrenheit. C -> F 0 C = ________ F -40 C = _______F F-> C 200 F = ______C 0 F = ________ C

Celsius vs. Fahrenheit

Absolute Zero In principle, there is no upper limit of temperature There is a definite lower limit to temperature (absolute zero is it) At absolute zero, molecules of matter have lost all available kinetic energy Absolute zero is the beginning of the Kelvin scale Degrees on the Kelvin scale are the same as degrees on the Celsius scale, but they start at a different point

Heat Moves? Matter does not contain “heat”. By definition: Matter contains “thermal energy”. Heat is thermal energy in transit. That is: when thermal energy is moving from one object or substance to another For objects/substances in contact, thermal energy flows from higher level (higher temperature) to the object or substance with the lower level (lower temperature) of thermal energy

Kelvin/Celsius/Fahrenheit

What is cold? Dark is the absence of light. Likewise, cold is the absence of heat. By definition, cold is not the opposite of heat, cold is simply a condition of less heat. When you touch something that feels cold, energy leaves you and goes into the cold object

Heat measurement Heat is a form of energy measured in units called Joules. It takes 4.18 Joules of heat to change 1 gram of water by 1 Celsius degree. In the USA, the unit “calorie” is often used instead of or along with Joules. A calorie is defined as the amount of heat needed to change 1 gram of water 1 Celsius degree. The energy value of foods are measured in calories. (Actually in kilocalories.) A Kcal is the amount of heat needed to change 1 kg of water by 1 Celsius degree

Food labels show the calories in food.

Specific Heat Some substance will stay hot longer than others. This ability to store/retain heat is called specific heat. Specific heat capacity is somewhat like inertia. Recall that inertia is a resistance to change in motion, specific heat is a resistance to a change of thermal energy Water has one of the highest specific heat values around. Water takes a lot of energy to heat up and a long time to cool down. That is why places near large bodies of water have moderate climates.

Thermal Expansion Increase in temperature occurs when the molecules of a material move faster. Particles moving fast take up more space than particles moving slow. When materials are heated, they usually increase in volume. This is called thermal expansion. Conversely, when substances get colder, they decrease in volume. Water does something strange, it expands when it changes from liquid to solid.

Expansion of water When water cools it contracts, until it reaches 4 degrees C. Then it expands. Once it freezes, it expands a lot. That is why ice floats. (The density of ice is less than the density of water.)

Heat Transfer-Conduction When you touch something that is hot, that is conduction. Substances that are not good conductors of heat are insulators. Air and snow are 2 really good insulators. They slow down the transfer of heat by conduction because the molecules that make them up have space between them, which makes it harder for one molecule to hit the next one.

Heat Transfer-Convection Heat transfer that occurs when heated fluids (gas or liquid) rises due to it expansion (decrease in density) tion?quick=an&att=758 tion?quick=an&att=758

Heat Transfer-Radiation/Radiant Energy Radiant energy is in the form of electromagnetic waves Radiant energy does not need a substance to travel through Radiant energy is very much like infrared radiation All objects emit some radiant energy. Which of the following DOES NOT give off radiant energy? A. volcanic lavaB. Red-hot coals C. IceD. A science book When would an ice cube be an emitter of radiant energy? When would ice be an absorber of radiant energy?

Reflection of Radiant Energy Light colored surfaces are better reflectors of radiant energy than dark surfaces. Once we get snowfall that sticks, what typically happens to the average daily temperature? Why? New term: Albedo. Albedo is the measurement of the ability of a surface to reflect light. Snow would have a high albedo, a black shirt would have a low albedo.

Energy changes during phase changes When matter changes phase, like when water freezes, ice melts, or water evaporates, there is a change of energy.