Question 1

What is temperature, actually?

Accepted Answer

A measure of the **average kinetic energy of the particles** in a substance — how vigorously they move, vibrate and rotate. It is not a measure of how much heat something contains, and separating those two ideas resolves most everyday confusion about it.

**Temperature versus heat.** A spark from a firework can be at over 1,000°C and cause no injury, because it contains almost no **energy** — very little mass moving vigorously. A bath at 50°C contains vastly more energy and will scald you. **Temperature is intensity; heat is quantity.**

**Why heat flows the way it does.** Energy transfers from higher to lower temperature until they equalise — not because anything is pushing it, but because that distribution is overwhelmingly the most probable arrangement. **Thermal equilibrium is a statistical outcome**, which is the deep connection between temperature and entropy.

**Why absolute zero cannot be reached.** At 0 kelvin, particle motion would be at its quantum minimum. Each step of cooling removes a fraction of the remaining energy, so reaching zero requires infinitely many steps. Laboratories have achieved billionths of a kelvin and never zero.

**Why the scales are as they are.** Celsius and Fahrenheit are defined around convenient reference points; **kelvin is defined from absolute zero**, which is why it is used in physics — ratios only make sense on an absolute scale. Twenty degrees Celsius is not twice as hot as ten.

**How thermometers work**, in order of what they actually measure: thermal expansion of liquid or metal; electrical resistance changing with temperature; the voltage generated where two dissimilar metals join, in a thermocouple; and **infrared radiation emitted by the object**, which is what non-contact thermometers detect — they measure emitted radiation and must assume a surface emissivity, which is why they misread shiny metal.

**The oddity worth knowing:** systems with an upper bound on energy can be assigned **negative absolute temperatures**, which are not colder than zero but hotter than any positive temperature — a genuine and counterintuitive result in statistical mechanics.

Question 2

What is absolute zero and why can't you reach it?

Accepted Answer

Absolute zero is 0 kelvin, equal to −273.15°C. It is the lowest possible temperature: the point at which a system has the minimum energy physically permitted. What temperature actually measures.

Question 3

Why is space cold if the Sun is so hot?

Accepted Answer

Because "cold" and "hot" are describing two different things, and space has almost nothing to do the transferring. Temperature is not the same as heat. Temperature measures the average kinetic energy

Question 4

What actually is fire?

Accepted Answer

Fire is not a substance or an object. It is a process — a self-sustaining chemical reaction — and what you see is the visible byproduct of that reaction. The chemistry. Fire is rapid combustion: fuel

Question 5

Why does metal feel colder than wood at the same temperature?

Accepted Answer

Your skin does not measure temperature. It measures how quickly heat is leaving or entering it. Metal and wood sitting in the same room are at the same temperature, but metal removes heat from your

Question 6

Why does hot metal glow red and then white?

Accepted Answer

Because everything emits light according to its temperature, and as temperature rises the emission shifts toward shorter wavelengths and broadens across the spectrum. Any object above absolute zero

Question 7

Can hot water really freeze faster than cold water?

Accepted Answer

Sometimes, under specific conditions — but the effect is inconsistent, and after decades of experiments there is still no agreed explanation. It is known as the Mpemba effect, after a Tanzanian

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