Interesting fact
Water is a better thermal conductor than air and conducts heat away from the body about 20 times more efficiently than air. A person who is not wearing a wetsuit, will lose heat very quickly to the water around them and can be vulnerable to hypothermia (this is when the body temperature drops very low). Wetsuits help to preserve body heat by trapping a layer of water against the skin. This water is then warmed by body heat and acts as an insulator. Wetsuits are made out of closed-cell, foam neoprene. Neoprene is a synthetic rubber that contains small bubbles of nitrogen gas when made for use as wetsuit material. Nitrogen gas has very low thermal conductivity, so it does not allow heat from the body (or the water trapped between the body and the wetsuit) to be lost to the water outside of the wetsuit. In this way a person in a wetsuit is able to keep their body temperature much higher than they would otherwise.
Investigation : a closer look at thermal conductivity
Look at the table below, which shows the thermal conductivity of a number of different materials, and then answer the questions that follow. The higher the number in the second column, the better the material is at conducting heat (i.e. it is a good thermal conductor). Remember that a material that conducts heat efficiently, will also lose heat more quickly than an insulating material.
|
Material |
Thermal Conductivity (
) |
| Silver |
429 |
| Stainless steel |
16 |
| Standard glass |
1.05 |
| Concrete |
0.9 - 2 |
| Red brick |
0.69 |
| Water |
0.58 |
| Snow |
0.25 - 0.5 |
| Wood |
0.04 - 0.12 |
| Polystyrene |
0.03 |
| Air |
0.024 |
Use this information to answer the following questions:
- Name two materials that are good thermal conductors.
- Name two materials that are good insulators.
- Explain why:
- cooler boxes are often made of polystyrene
- homes that are made from wood need less internal heating during the winter months.
- igloos (homes made from snow) are so good at maintaining warm temperatures, even in freezing conditions.
Interesting fact
It is a known fact that well-insulated buildings need less energy for heating than do buildings that have no insulation. Two building materials that are being used more and more worldwide, are
mineral wool and
polystyrene . Mineral wool is a good insulator because it holds air still in the matrix of the wool so that heat is not lost. Since air is a poor conductor and a good insulator, this helps to keep energy within the building. Polystyrene is also a good insulator and is able to keep cool things cool and hot things hot. It has the added advantage of being resistant to moisture, mould and mildew.
Remember that concepts such as conductivity and insulation are not only relevant in the building, industrial and home environments. Think for example of the layer of blubber or fat that is found in some animals. In very cold environments, fat and blubber not only provide protection, but also act as an insulator to help the animal keep its body temperature at the right level. This is known as
thermoregulation .
Magnetic and non-magnetic materials
We have now looked at a number of ways in which matter can be grouped, such as into metals, semi-metals and non-metals; electrical conductors and insulators, and thermal conductors and insulators. One way in which we can further group metals, is to divide them into those that are
magnetic and those that are
non-magnetic.
