Nina Marie Alban IV-Bacquerel

*History of Heat

*Even in the ancient times, it was understood that light and heat are different. Fire was considered to be one of the elements, but the ancients had noticed that while the fire burned it give light and heat but after it subsided the embers continued to give heat.

*Joseph Black – He noticed that a kettle filled with water and ice placed over a fire did not change in temperature till all the ice was melted. He suggested that heat flows like a fluid.

*What is HEAT?

*Heat is thermal energy that is absorbed, given up or transferred from one body to another.

*The temperature of a body is a measure of its ability to give up heat to, or absorb heat from another body. (modern physics p.167)

*What are the sources of HEAT?

• The sun is the primary source of heat energy.• Most of the

sun’s heat is radiated back into space and only small amount of it reach the earth to keep it warm.

Rubbing or Friction – heat can be produced when two objects are being rubbed together.

Burning- is one of the common ways of producing Heat. When something burns, it produces flame and also heat.

Electricity

*What are the effects of HEAT?

*Thermal Equilibrium•Heat flows from warmer objects to cooler

objects. When a warmer object is in contact with a cooler object, it will transfer heat to the cooler object. •This will go on until both objects have the same temperature. At this point, they are in the state of thermal equilibrium.•For example, a bottle of soda is taken out from refrigerator and placed on a table. The table which is at room temperature, will transfer heat to the bottle. Eventually, their temperature will be equal and thermal equilibrium will be achieved.

*Expansion &Contraction of Matter

•Most matter expands when heated and contracts when cooled.

•Two common examples of the effects of heat are a boiled egg and a thick glass cracking when hot water is poured onto them.

•The increase in size of objects when they are hot is called expansion. The decrease in their size when they are cooled is called contraction

*Expansion & Contraction of Solids

•The atoms or molecules in a solid vibrate at all temperatures.

•As the temperature increases, they vibrate more vigorously and this pushes the atoms further apart. The volume of the solid increases and the expansion is said to occur.

*Expansion and Contraction of Liquids

*When a liquid is heated, the molecules of the liquid have more energy and move more vigorously. The movement of the molecules gradually overcomes the forces of attraction between molecules, allowing them to have greater freedom to move over greater volumes. Thus, the liquid expands.

*Expansion and Contraction of Gases

•The molecules of a gas are far part compared with the molecules in a solid and a liquid. The gas molecules move at a high speeds in all direction.

• If a gas is confined in a container whose volume is variable, the volume of the gas will increase with increasing temperature. The volume will decrease as the temperature drops.

*Thank you!!