What is temperature?

Temperature measures the average kinetic energy of particles (atoms or molecules) in a substance in other words, how fast the particles inside something are moving or vibrating.

When you heat a substance, particles get more energy and move faster. Temperature captures that average speed.

Three main scales:

• Celsius: water freezes at 0, boils at 100 used worldwide in daily life
• Fahrenheit: water freezes at 32, boils at 212 used in the US
• Kelvin: starts at absolute zero (0 K = -273.15°C) used in science and physics

Absolute zero (0 K): the temperature at which particle motion essentially stops. Nothing can be colder. Never perfectly achieved, though lab experiments have come extremely close.

Temperature vs heat: a bathtub of warm water has more total heat than a cup of boiling water, but the cup has a higher temperature. Heat is total energy; temperature is intensity per particle.