AI Tutor
If you leave an ice pop on a sunny sidewalk, it turns into a puddle in minutes. But if you pour juice into an ice tray and slide it into the freezer, it turns solid.
What invisible power turns hard ice into liquid water and back again?

Thermal Energy and Tiny Particles

All matter is made of tiny bits called particles that never stop moving. Thermal energy is the total energy of all those moving particles inside an object.
When an object gets hotter, its particles move faster and push slightly apart. When an object cools down, its particles slow down and move closer together.
So what happens when solid particles absorb so much energy that they can no longer hold still?

Adding Heat: Melting

Melting is the phase change from a solid to a liquid when thermal energy is added. For pure water, this happens at 0 degrees Celsius (0∘C0^\circ\text{C} or 32∘F32^\circ\text{F}), which is called its melting point.
As heat flows into an ice cube, the locked particles vibrate faster and faster until they break free from their rigid pattern and slide around as liquid water.
What happens if we reverse the process and take that thermal energy away?

Removing Heat: Freezing