3 Types of Heat Transfer

Heat Transfer- The movement of heat from a warmer object to a cooler object.

1. Conduction Heat transfer by direct contact of molecules. In other words, when one molecule runs into another and it runs into another, etc. It can occur in a solid, liquid or a gas. Occurs best in a solid because the molecules are close together.

conduction

2. Convection Heat transfer by means of up and down movements called convection currents. Can occur only in a liquid or a gas

Convection currents Heated molecules do 2 things: 1. they expand, become less and then.. 2. they rise. Cooled molecules do the exact opposite: 1. they contract, become more dense and then… 2. they sink That is what makes a hot air balloon rise.

3. Radiation Heat transfer through open space. Occurs in a gas only.

Chapter 5 Section 1Fall 2005, Pflugerville ISD Energy comes in many forms: –Thermal energy –Chemical energy –Electrical energy –Sound energy –Light energy –Nuclear energy What is Energy? Cite:

Chapter 5 Section 1Fall 2005, Pflugerville ISD Thermal energy is the total energy of the particles that make up an object. Because the particles are moving, they have kinetic energy. –At higher temperatures, the particles move faster –The faster particles move, the more kinetic energy they have and the greater the object’s thermal energy is Thermal energy also depends on the number of particles in a substance. What is Energy?

Chapter 5 Section 1Fall 2005, Pflugerville ISD Chemical energy is the energy stored in a substance that can be released when the substance reacts. For example - when wood is burned, chemical energy is released. Another example - when you eat something, your body is able to use the food’s chemical energy. What is Energy?

Chapter 5 Section 1Fall 2005, Pflugerville ISD Electrical energy is the energy of moving electrons. When you plug in your alarm clock and turn it on, electrons in the wires move back and forth (120 times per second). As the electrons move, energy is transferred to different parts of the clock to make it do work. What is Energy? Cite: Cite:

Chapter 5 Section 1Fall 2005, Pflugerville ISD What is Energy? Sound energy is caused by an object’s vibrations. When a guitar string vibrates, energy is transferred from the moving string to the air particles around it. The particles transfer energy from one another and finally cause your eardrum to vibrate, and you hear the sound of the guitar.

Chapter 5 Section 1Fall 2005, Pflugerville ISD Light energy is caused by the vibrations of electrically charged particles. The vibrations that transmit light energy do not require particles to transmit energy. Light energy, unlike sound energy, can be transmitted through a vacuum (like space). What is Energy?

Chapter 5 Section 1Fall 2005, Pflugerville ISD What is Energy? Nuclear energy is caused by changes in the nucleus of an atom. Nuclear energy is produced two ways: –When two or more nuclei join together (nuclear fusion) –When the nucleus of an atom splits apart (nuclear fission)

Chapter 5 Section 2Fall 2005, Pflugerville ISD The Law of Conservation of Energy states energy can neither be created nor destroyed. The total amount of energy in a closed system is always the same. Energy Conversions

Chapter 5 Section 3Fall 2005, Pflugerville ISD Heating systems move thermal energy to cooler areas. Air or water is used to move thermal energy from burning fuel to other areas of a house or building. Using Energy

Chapter 5 Section 3Fall 2005, Pflugerville ISD Solar heating systems convert light energy from the sun into thermal energy. Active solar heating systems have moving parts – machines that move the sun’s energy throughout a building (such as pipes, fans, and storage tanks for water to be heated). Passive solar heating systems do not have moving parts – they use thick walls and large windows that face south. Using Energy