lesson
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If you hold an ice cube, your hand feels freezing cold. But how cold is it really?
To know the exact warmth or coldness of an object, we measure its temperature using a unit called degrees Celsius (ext°C).
In 1742, Swedish scientist Anders Celsius invented this scale by setting the freezing point of pure water at 0ext°C and the boiling point at 100ext°C.
📊A colorful horizontal benchmark bar showing degrees Celsius (°C) milestones for primary students: 0°C (Ice freezing / snowman icon), 20°C (Comfortable room temperature / house icon), 37°C (Normal human body temperature / smiling person icon), and 100°C (Boiling water / steaming kettle icon). Clean minimal styling, light background #f8f9fa, blue accent for cold, red accent for hot, bold clear text labels.
How does a narrow glass tube tell us the exact temperature?
Inside a Liquid Thermometer
A liquid-in-glass thermometer has colored liquid inside a bulb. When the liquid warms up, it expands (gets bigger) and climbs up the tube; when it cools, it shrinks and drops.
Before you read a thermometer, always check the scale to see how much each small tick mark represents.
📊An interactive-style visual diagram of a liquid-in-glass thermometer tube. On the left, show a scale where every mark is 1°C (marks at 20, 21, 22, 23, 24, 25). On the right, show a scale where each tick mark represents 2°C (marks at 10, 12, 14, 16, 18, 20). Include an eye icon pointing horizontally straight at the top meniscus of the red liquid at 24°C with a green checkmark, and tilted sightlines with red X marks labeled 'Wrong: looking from above or below'.
Let's read a scale counting by 2s: if the liquid is two marks above 20ext°C, you count 20,22,24ext°C.
Always look straight at the liquid level with your eyes flat and level. Looking from above makes the temperature look too low, while looking from below makes it look too high!
What happens if the weather gets even colder than freezing ice?