Temperature and Heat

Programme Outline

This programme is concerned with the measurement of temperature and the nature of heat. Thermal imaging is used to give a new perspective on heat in everyday life. The history of the thermometer is outlined to show the importance of a standard scale for temperature measurement. How can we measure the temperature of red hot-iron, or liquid air? What is heat and how do things cool down? How can you make instant ice cream?

The programme is divided into four main sections:

1. Imaging techniques using infra-red
2. Sensing temperature
3. How thermometers work
4. Temperature, heat and the movement of particles

00.00–03.23
How can you see in the dark?

A police helicopter is using Forward Looking Infra-Red to track a group of suspects. The contrast between the warm bodies of the suspects and the cold background allows the pilot to pick them out. A tour around the supermarket, a hot drink and a cold shower all look very different in infra-red.

03.23–05.02
How does our sense of temperature work?

We use our skin to feel how hot or cold something is, but we are not very good at judging the temperature of a swimming pool. A simple investigation with bowls of warm and cold water shows that our sense of temperature is based on comparison.

05.02–06.16
The invention of air thermometers

Doctors used to place their hand on a patient’s forehead to help with diagnosis, but they needed a more reliable method of measuring temperature. Early thermometers consisted of a large round flask with a long tube attached. Introduce a coloured liquid by warming and cooling and you have a thermometer.

06.16–07.52
How does an air thermometer work?

The air thermometer works because a gas expands when it is warmed. A graphic simulation shows how the gas particles have more energy and so move apart from each other. A smaller bulb allowed the doctor to get it into the patient’s mouth. Early temperature measurements were made by the doctor marking their own temperature on the glass tube and comparing it with that of the patient.

07.52–11.00

The Celsius scale

In the eighteenth century there were many types of thermometer, and many temperature scales. A standard scale was needed, so that temperatures taken by different thermometers could be compared. A visit to a modern thermometer factory shows how a liquid thermometer is made and the standard Celsius scale is marked on it.

11.00–11.51
Different thermometers for different jobs

Not all thermometers look the same. A montage of devices used to measure different temperatures takes us up and down the scale, from red-hot metal to liquid nitrogen.

11.51–13.30
How do things warm up and cool down?

In the kitchen we investigate why milkshakes are cool, but chocolate can be hot. The thermal imaging camera and three-dimensional graphics help to explain how energy from hot chocolate can pass to a cool milkshake, until everything is at the same temperature. What can you say about the energy of the particles in both drinks now?

13.30–18.30
Making instant ice cream using heat transfer

The same principle allows a couple of crazy chefs to make instant ice cream in seconds using liquid nitrogen. But if you want to try this at home, all you need is ice, salt and plenty of energy for shaking. Graphic overlays help to explain how energy flows from the ice cream mixture to the ice and salt. Shaking speeds up the process by bringing the warmer and colder particles together until all the particles have about the same amount of energy.

18.30–end
Calculating the amount of heat in an ice cream

Which has more energy, the particles in a small bowl of ice cream, or the particles in a large tub? They’re both at the same temperature, but the large tub has more particles, so it has more energy.