Energy and Heat

What is Energy? When something is able to change its environment or itself, it has energy Energy is the ability to change Energy has several different forms, such as electrical, chemical, mechanical, light, nuclear, and thermal

Energy Forms

Kinetic Energy Kinetic energy is energy in the form of motion The amount of kinetic energy depends on the mass and velocity of the object The kinetic energy of an object can be calculated using the following relationship: Kinetic energy = ½ mass X velocity2 KE = ½ m X v2 The joule is the SI unit of energy

Kinetic Energy

Potential Energy Potential energy is stored energy The amount of potential energy depends on its position or its condition Potential Energy can be calculated using the following equation: Potential Energy = weight X height Weight = mass X Gravity (9.8 m/s2) PE is measured in joules Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring Energy can be stored in the chemical bonds between atoms Energy stored in chemical bonds is chemical potential energy

Potential Energy

Conservation of Energy Energy may change from one form or another, but the total amount of energy remains constant Energy cannot be created nor destroyed This statement is known as the law of conservation of energy

Energy Forms Energy can change from one form to another Energy can be found in the form of: nuclear mechanical chemical thermal light electrical

Energy Conversion in a Car

Energy Conversion in a Coal Plant

Temperature Temperature is the measure of the average kinetic energy of the particles in a sample of matter. In SI units, temperature is measured in Kelvin (K) (273 + °C). A change in state due to temperature involves a transfer of energy from a warm/hot object to a cool/cold object.

Thermal Energy Like temperature, thermal energy is related to the energy of the particles that make up matter. Thermal energy is the total energy of the particles in a material. This includes both kinetic and potential energy. Thermal energy of an object increases as its temperature increases. The more mass a material has at the same temperature, the more thermal energy it has.

Heat Heat is the thermal (or internal) energy that flows from something with a higher temperature to something with a lower temperature. Heat is a form of energy, so it is measured in joules In most cases, heat flows from warmer to cooler materials.

Specific Heat Different materials need different amounts of heat to produce similar changes in their temperatures. The specific heat (C ) of a material is the amount of energy it takes to raise the temperature of 1 kg of the material 1 kelvin. Specific heat is measured in joules per kilogram kelvin [J/(kgK)].

Change in Thermal Energy Change in thermal energy = mass X change in temperature X specific heat or Q = m X ΔT X C When ΔT is positive, Q is also positive; the object has increased in temperature and gained thermal energy. When ΔT is negative, Q is also negative; the object has lost thermal energy and decreased temperature.

Movement of Thermal Energy Conduction is the transfer of energy through matter by direct contact of particles. Conduction takes place in solids, liquids, and gases. The most important way thermal energy is transferred in fluids is by convection. Convection is the transfer of energy by the bulk movement of matter. In conduction, energy moves from particle to particle, but the particles themselves remain approximately in place. In convection, fluid particles move from one location to another, carrying energy with them. Radiation is the transfer of energy in the form of waves. Good insulators do not allow heat to move easily through them.

Movement of Thermal Energy

Forced-Air System The most common type of heating system in use today is the forced-air system. In this system, fuel is burned in a furnace and heats a volume of air. A fan then blows the warm air through a series of large pipes called ducts. The ducts lead to openings called vents in each room. Cool air returns through the furnace through additional vents, where it is reheated.

Forced Air System

Radiators and Electrical Heating Systems A radiator is a closed metal container that contains hot water or steam. The thermal energy contained in the hot water or steam is transferred to the air surrounding the radiator by conduction. This warm air then moves through the room by convection. An electrical heating system has no central furnace as forced-air and radiator systems do. Instead, it uses electrically heated coils placed in ceilings and floors to heat the surrounding air by conduction. Convection then distributes the heated air through the room.

Radiators and Electrical Heating Systems

Using Heat to Do Work Combustion is the process of converting chemical energy to thermal energy. During combustion, a fuel combines with oxygen and produces heat and light. The thermal energy that is produced is then converted into mechanical energy. An engine that converts thermal energy into mechanical energy is called a heat engine. A heat engine is called an internal combustion engine because fuel is burned inside the engine in chambers, or cylinders. A heat mover is a device that removes thermal energy from one location and transfers it to another location at a different temperature. Refrigerators, air conditioners, and heat pumps are examples of heat movers.

Heat Engine

Heat Movers