ACARA v9 CONTENT DESCRIPTION “identify sources of heat energy and examine how temperature changes when heat energy is transferred from one object to another”
Builds on noticing that some things feel hot and some feel cold. Here we name the things that give off heat, and we use a thermometer to measure how warm something is instead of only guessing with our hands.
Heat energy comes from sources
Some things give off heat energy. We call them heat sources. The Sun, a fire, a switched-on stove and even your own hands rubbing together all make heat. When heat reaches an object, the object gets warmer.
Where does heat come from?
Heat energy comes from a source. Tap each one to see how it gives off heat.
The Sun warms the whole Earth from far away in space. All of these are sources of heat energy.
Temperature tells us how hot
Temperature is a number that tells us how hot or cold something is. We measure it with a thermometer, and we write it in degrees, like 20°C. When heat energy is added, the temperature reading goes up. When heat is taken away, the reading goes down.
A thermometer reads the temperature
Temperature tells us how hot something is. Add heat and the thermometer reading goes up.
The reading is 20°C. When something gets hotter the column climbs, and when it cools the column drops. The thermometer lets us measure the change instead of just guessing.
Heat moves from hot to cold
When a hot object touches a cooler object, heat energy moves from the hotter one to the cooler one. That is why a warm cup heats your cold hands, and not the other way around. Heat always travels in this one direction: from hot toward cold.
Heat moves from hot to cold
When a hot thing touches a cold thing, heat energy travels from the hotter one to the cooler one.
Tap "Hold the cup" to join the hot cup and the cold hands. Watch which way the heat arrow points.
Until they are the same
The heat does not move forever. As the hot object cools and the cool object warms, the gap between them shrinks. Once both objects reach the same temperature, the heat stops moving and they stay equally warm together.
They meet in the middle
When a hot block and a cold block touch, heat keeps moving until both reach the same temperature.
The hot block is 80°C and the cold block is 20°C. Wait again and watch the gap between them shrink as heat passes from hot to cold.
Measuring lets us compare
With a thermometer we can put a number on how warm each thing is. Then we can compare them fairly: a higher number always means warmer. Measuring is better than guessing, because two things that both feel cool can still be at quite different temperatures.
Measure and compare
We use a thermometer to measure things, then compare which is warmer and which is cooler.
The your hand measures 30°C, so it is a warm thing. Measuring lets us compare fairly: a bigger number on the thermometer always means warmer.
Why this matters
Heat is all around us, from warming our food to keeping us comfortable. Knowing where heat comes from, that it moves from hot to cold, and how to measure temperature helps us cook safely, dress for the weather and understand the world around us.
Quick self-check
1. Which of these is a source of heat energy?
2. What do we use to measure how hot or cold something is?
3. A hot cup of cocoa touches your cold hands. Which way does the heat move?
4. A hot block and a cold block touch and are left for a while. What happens to their temperatures?
5. When you add heat energy to water, the thermometer reading...