7.3 HEAT FLOW.1. Heat energy travels from one place to another as a result of differences in

temperature.2. When two objects are brought into contact, heat energy will flow from a

hotter object to a cooler object. 3. As a result, the temperature of cooler object rises, while that of the hotter

object falls.4. The flow of heat energy will stop when the objects in contact have reached

the same temperature.5. The rate of heat transfer depends on the difference in temperatures between

two objects. The greater the difference in temperature, the faster rate of heat flow.

6. Heat is transferred in three different ways:

A. CONDUCTION1. Conduction is the transfer of heat energy through solids.2. The particles in the medium do not flow.3. Heat is transferred from the hotter end of the object to the cooler end by the vibration of particles in the object.

4. Different materials conduct heat at different rates.5. Generally, metal such as copper, iron, aluminium and silver are good conductors of heat.6. Non-metal such as wood, glass plastics and rubber are poor conductors and are called insulators of heat.

The thumbtack that is stuck to the copper rod drop first. This is followed, in order, by

the thumbtack stuck to aluminium rod, iron rod and glass rod.

This is because different materials conduct heat at different rates.

B. CONVECTION1. Convection is the transfer of heat from one part of a fluid (substances which

can flow) to another by the circulating movement of the heated fluid.2. Liquid and gases are fluids.3. This circulating movement is called a convection.

C. RADIATION

1. Radiation is a process of heat transfer that does not require a medium.2. Radiation can take place in a vacuum.3. Properties of radiant heat:

i. Travels as electromagnetic waves.ii. Travel at the speed of lightiii. Travels in straight lineiv. Travel through vacuumv. Can be absorbed or

reflected.4. The heat from the Sun is

transferred to the Earth by radiation.

HEAT FLOW IN NATURAL PHENOMENAA. SEA BREEZE

1. During day time, both land and sea absorb heat from the Sun. However, the land gets heated up faster than the sea.

2. As a result, the air on land becomes less dense and rises.3. The cooler air over the sea which is denser moves toward the land. This

movement is called sea breeze.

B. LAND BREEZE1. At night, the land cools faster than the sea.2. The sea becomes warmer than the land. The hot air above the sea less

dense and rises.3. Cool air from the land moves in to take its place.4. This movement of air is called land breeze.

C. THE WARMING OF THE EARTH BY THE SUN1. The Earth and the Sun is separated by vacuum.2. The heat from the Sun travels as energy waves called infrared.3. The infrared waves travel through vacuum in space to reach the Earth by

radiation.4. The Earth and its atmosphere are warmed by radiation.

HEAT CONDUCTORS AND HEAT INSULATORSCONDUCTORS

1. A heat conductor is a substance that allows heat to move through it easily.2. Metals are good conductors of heat.3. Examples: mercury, silver, copper, aluminium, zinc, iron and lead.

INSULATORS1. An insulator is a substance does not conduct heat easily.2. Insulator also called poor conductors of heat.3. Generally, non-metals are good insulators.4. Examples: air, cork, water, glass, cotton, plastic, rubber, wood and

polystyrene.

THE USES OF CONDUCTORS AND INSULATORS OF HEAT