Heating and Cooling

Energy: Heat Transfer

Heat is the name for the type of kinetic energy possessed by particles.

If something gains a lot of heat energy, it becomes hot - so what is temperature?

Temperature is a measure of the hotness or coldness of something, not the total amount of energy contained.

Temperature is measured in degrees Celsius (or centigrade) - ºC.

Temperature measurement

The freezing point of water is DEFINED as 0oC (at 1 atm.). The boiling point of water is DEFINED as 100oC (at 1 atm.).

The temperature can be measured in a variety of different thermometers. These include liquid in glass, digital, thermocouple and bimetal strip thermometers.

The Particle Model

The existence of solids, liquids and gases is

explained by the following ideas:1. All substances are made up of

particles (atoms, ions and molecules).2. That these particles are attracted to

each other, some strongly and others weakly.

3. That these particles move around (i.e. Have kinetickinetic energy).

4. That their kinetic energy increases with temperature.

Which would feel warmer if we picked up a piece of wood and a piece copper metal both at room temperature (i.e. both at 250C)?

The wood feels warmer because it is a POOR conductor. So it would not conduct heat away from your hand as quickly as the copper.

Energy : heat transfer

Temperature

What’s the temperature?• The coldest place on Earth

is Antartica, where temperatures as cold as -89˚C have been recorded.

• At the other extreme, the hottest place on Earth is the El Alzizia desert in Libya where temperatures have soared to 58˚C.

• But what exactly do we mean by hot and cold?

The Celcius temperature scale• We measure temperature

to tell us exactly how hot or cold something is. To do this we use a thermometer, which has a scale on it. The celcius temperature scale is based on two fixed points, the melting point of ice (water) and the boiling point of water at normal atmospheric pressure. The melting point of water is called 0, and the boiling point is called 100. There are 100 divisions or degrees between these two points.

Make your own thermometer

• If you had a thermometer without a scale, you could make your own scale. Dip it in melting ice for a few minutes and mark off the reading: this is 0˚C. then put it in boiling water and mark off this reading: 100˚C. Then divide the distance between the two fixed points into 100 equal units.

The right thermometer for the job

• There are different thermometers for different jobs. For example, your body temperature is 37˚C but the temperature in a freezer might be -20˚C. You need different thermometers to measure a range of temperatures, from the hottest to the coldest on its scale

The right thermometer for the job

• Some thermometers have a liquid in a a bulb. The liquid expands when it becomes warm, and the level moves up the tiny capillary tube inside. You read where the top of the liquid has got to on the scale. But not all thermometers are like this – there are lots of different kinds. Digital thermometers show you the reading in numbers.

What’s the difference between heat and temperature?

• Heat is a type of energy. We call it heat energy or thermal energy. Like other forms of energy it is measured in Joules (J).

• Heating is the transfer of thermal energy. Heat flows from one thing to another when there is a temperature difference. It flows from the hotter thing to the cooler thing.

Heat flows from hotter flame

Cooler metal pan

Cooler oil inside pan

What’s the difference between heat and

temperature?• The oil gets hotter because it is

supplied with thermal energy. As a result, its temperature rises. If you stopped heating the oil, thermal energy would float away from it, into the coller air around it. Then the oil would get colder again and it’s temperature would fall. The thermal energy is transferred to the oil through the metal pan. It is transferred by conduction. Conducting means transferring. Heat is conducted through any kind of material, but some materials are better than others. Metals are good conductors.

Revision

• We use a thermometer to measure temperature.

Measure to here

The Celsius scale of temperature

• At 0oC water will freeze into a solid.

• At 100oC water will boil and turn into steam.

• The range between these two points is divided into 100 segments known as the Celsius temperature scale.

Freezing point

Boiling point