Class Notes

Chaps. 4-5

The rate at which energy is transformed is called power. A stretched rubber band situation involves primarily potential energy. The energy of position is potential energy. The final total energy of a system always equals the initial total energy, called energy conservation law. A 1.0 hp engine compared to a 0.50 hp engine can do twice the work in the same time. Expansion property of materials is used in making the thermometers. The following properties does not change with temperature: volume, the state of a material, and length. The volume of a gas is directly proportional to its Kelvin temperature. The direction in which heat is conducted between two bodies depends on their temperatures. A drop of alcohol feels cool on your skin because heat is absorbed from your skin. The quantity that tells how warm or cold a body is with respect to some standard body is called temperature. A hot-water bottle contains 1 kilogram of water, as it cools from 70 deg C to 20 deg C it gives off 50 Kcal. If you warm your hands by holding them to one side of a flame, heat transfer is primarily by radiation. Absolute zero on the Fahrenheit scale is -460 deg F. A solid-gas phase change is called sublimation. A person carries their 10 N books at constant speed down a 5 m hall. How much work is being done? zero J. A cat when allowed to fall always lands on its feet. The cat is using conservation of angular momentum. Astronauts in space appear weightless because they are in free fall. Every person in your classroom is exerting a gravitational force on you, yet you do not feel this force because the force due to gravity is so small. Our Moon is simply a projectile freely falling around the Earth.

Calculate the heat energy required to raise 0.50 kg of water from 39 deg C to 50 deg C. The answer is 5505 cal or 23023 J. Convert 250 K into deg C and deg F.

In winter, light-colored clothes will keep you warmer than dark-colored clothes if you are warmer than your surroundings. Temperature measurement in liquid-in-glass thermometers is based on thermal expansion. The upper limit of temperature is unknown. Water has a negative thermal expansion over the temperature range of 0 to 4 C . Forced air home heating is an example of heat transfer by convection. The smallest temperature unit is a Fahrenheit degree. Convert 92 deg. F to Kelvin. The heat of fusion is the quantity of heat liberated when a unit mass a liquid to a solid. The boiling point of water is given as 100 on which temperature scale? If you sand a rusty metal, the sandpaper gets hot because friction creates the heat. The sunburn is caused by the radiation. If the mass and velocity is tripled, the kinetic energy is increased by a factor of 3. Power is work times time. P = work multiplied time. When a driver brakes a car to a stop, the energy of the moving car is converted to heat. The process of heat transfer may take place in a vacuum is convection.

Note: Do assigned problems!