Physics
Temperature & heat
Why your tea goes cold and what particles have to do with it.
What you need first
You blow on your hot cocoa, put on gloves in winter, and in summer you'd rather not touch the black car roof. It's always about warm and cold. But what exactly is warm in there? The answer lies in particles far too small to see.
Everything jiggles
Everything around you is made of tiny particles, and these particles never stand still. They tremble, whirl, and constantly bump into each other. Temperature is a measure of how vigorously they jiggle: in hot water the particles dash around wildly, in cold water they move only sluggishly. So a thermometer basically measures particle jiggling.
Water (liquid). Particles move faster.
Heat flows from warm to cold
When a warm and a cold body touch, the fast particles pass energy to the slow ones with every collision. This travelling energy is called heat, and it always flows from warm to cold, never the other way. That's why your tea goes cold and the ice in your hand melts: both adjust to their surroundings. The flow only stops once both sides have the same temperature. So if you mix equal amounts of hot and cold water, they meet roughly in the middle between the two temperatures. Important: temperature and heat are not the same. Temperature describes the state of a body, heat is the energy flowing between bodies.
The Celsius scale
So that everyone measures the same, the Celsius scale has two fixed points set by water: at normal it freezes at 0 °C and boils at 100 °C. Everything you know from daily life lies in between: about 20 °C in the living room and 37 °C in your body. Below 0 °C the scale carries on into the minus , so a winter morning at −4 °C sits 4 degrees below the freezing point.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
In which direction does heat flow by itself?
At how many °C does water freeze?
At how many °C does water boil at normal air pressure?
When two bodies touch, heat always flows by itself from … to cold, never the other way.
What does a high temperature mean in the particle model?
Match each temperature on the Celsius scale to the fitting situation.
Where this leads