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Heat
Heat
Introduction
Introduction
Heat is a form of energy that we need all the time. Heat affects most everything we do, what we wear and the types of houses we live in. If the sun should cool, all life on earth would disappear and it would be just a cold, dead mass much like moon. Heat is both our servant and our enemy. Using heat we can move trains, ships, and airplanes, but heat can also bum.
All materials or substances are made up tiny particles called molecules. It is taught that these molecules are in constant motion or vibration. Because they are moving, they have kinetic energy called heat.
Heat can travel from one place to another in three ways:
- Conduction
- Convection
- Radiation
Conduction is when heat moves from one molecule to another molecule. This is where the molecules near the sources of heat become hot, move faster, and strike the molecules next to them, causing them to move faster and get hotter.
Convection is when heat is transmitted by currents of gases or liquids. Warm air from a stove is pushed up by the colder, heavier air around it. The air circulates and warms the room.
This unit is an introduction into the fascinating area of physics called heat.
Radiation is when heat is transmitted through air or space by means of waves (electromagnetic waves). It does not require any particles to transfer the heat. Our best example of radiation is the heat that reaches us from the sun.
SOME BASIC FACTS
SOME BASIC FACTS
Temperature
Temperature
The temperature of something tells you how hot or how cold it is. Temperature is a measurement of heat or cold.
It is usually measured in degrees centigrade. Pure water freezes at 0° C and boils at 100° C at sea level under one atmosphere of pressure.
If you are well, your body temperature is about 37°C. We use a thermometer to measure the temperature of a room, body, weather and etc.
Hot things have a high temperature and cold things have a low temperature.
Thermometers
Thermometers
Temperature measures the degree of hot or cold of an object. The correct scientific definition is – the average internal kinetic energy of the particles of matter.
In the laboratory we usually make use of a laboratory thermometer (Direct reading thermometer). This thermometer can measure temperatures from -100C up to 1100C.
Please note the following facts:
Pure water boils at 100oC (at sea level and under 1 atmosphere of pressure)
- Pure water freezes at 00C (at sea level and under 1 atmosphere of pressure)
- Temperature is affected by height above/below sea level
- A clinical thermometer is different to the direct reading thermometer (see diagrams)
- The units used to measure temperature are; degrees centigrade (0C); degrees
- Fahrenheit (0F) and you will often hear Kelvin being used to measure temperature Thermometers are usually filled with alcohol –either coloured red or blue) or mercury as they are liquids able to expand and contract pretty quickly.
Structure of a thermometer
The thermometer consists of a glass tube which has a thin capillary tube in the centre. The capillary tube ends in the bulb or reservoir. The glass tube is sealed to keep a partial vacuum in the capillary tube.
This vacuum allows the liquid to expand and contract. On the outer wall of the glass tube is a marked scale. Depending on The liquid you will either read the top/bottom of the meniscus.
(Please remember the Error of parallax). The thermometer can measure from -100C to 1200C.
One problem students experience is reading the temperature accurately:– they often remove the thermometer from the liquid and find the temperature changing.
Because it is a direct reading thermometer, the thermometer must remain in the liquid you are heating/measuring.
Units for measuring temperature
Units for measuring temperature
There are two main units used for measuring temperature:
- Celsius ( the universal system)
- Fahrenheit
In the early eighteenth century, Gabriel Fahrenheit (1686-1736) created the Fahrenheit scale. He set the freezing point of water at 32°F and the boiling point at 212°F. These two points formed the anchors for his scale.
Later in that century (1743), Anders Celsius (1701-1744) invented the Celsius scale. Using the same anchor points, he determined the freezing temperature for water to be 0°C and the boiling temperature 100°C.
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