Week 16 - Heat vs Temperature, Volume, Conduction, Convection and Radiation
Lesson 2.1: Heat and Temperature
Science in Action 7 pages 198 to 202 or Science Focus 7 pages 204 to 207
Mercury is a solid at -40°C, but alcohol is still a liquid. Why? Because the attractive forces are stronger between the mercury particles than the attractive forces between the alcohol particles.
Recall earlier that we learned that there are attractive forces between the particles in a substance. But these attractive forces are different from substance to substance. Some substances have very strong attractive forces, while other substances have weaker forces. So, now knowing this, why do you think mercury turns solid while the alcohol does not?
Heat and temperature, although related words, do not mean the same thing. Heat is the amount of energy contained in the moving particles. Heat always flows from an area of higher temperature to an area of lower temperature. Temperature is the measure of how hot or cold something is. Temperature is the average kinetic energy of the particles of a substance. Why is it the average kinetic energy?
Let's use a pot of water on the stove for an example. Those particles near the bottom of the pot will have more kinetic energy that those nearer the top of the pot because the bottom is nearer the heat source, so all the particles in the pot are not moving at the same rate - they don't all have the same kinetic energy. The average of all the energy levels in the pot would be its temperature.
What is needed is a more accurate way of determining the temperature. Thermometers are devices use to measure temperature. There are two main types of liquid thermometers. Most are filled with an alcohol solution and can be used even a very low temperatures below -40°C. Some thermometers are filled with a shiny liquid metal called mercury. But mercury changes from a liquid to a solid at -39°C and leaving them out below this temperature causes the thermometer to break.
Knowing how hot or cold something is can mean a matter of life and death. Humans have an average body temperature of 37°C and can only stray from that temperature a few degrees without getting into real danger.
Hypothermia is a term that is used to describe a critical lowering of body temperature. Every year in Canada, many people die from hypothermia.
Heat stroke is a condition caused by your body temperature being to high. Death from heat stroke is more common in very warm environments.
ACTIVITY A: Can your senses be trusted?
Did You Know?
Many people who have suffered from hypothermia have actually removed clothing because they felt too warm, when all the while they were actually freezing to death!
Throughout our lives we rely on our senses to tell us what's happening in our environment. But just as our eyes can be tricked with optical (visual) illusions, other senses, such as heat detection, can also lead us astray. In this activity you will be using the sensory endings in your hands to tell you when liquids are hot or cold.
Complete this activity with the supervision of a parent, guardian or other adult.
1. Gather up three buckets. Two must be large enough so that you can place one hand inside each. These will be used for containers 1 and 3. The third, must be large enough so that both hands can fit in it at the same time (container #2).
2. Half fill the containers as shown below.
Caution! The water should feel hot, but not uncomfortable or burning hot!
3. Place one hand in container 1, and the other in container three. Leave them there for one minute.
4. After one minute take your hands out of the two buckets and place them both in container number 2.