Do you know what you are made of?

One answer is that you are made of flesh, blood, and bone.
Another answer is that you are made of atoms and molecules. Atoms are tiny bits of matter that join together to make everything in the world. An atom is over a million times smaller than the thickness of a human hair. Atoms come together to form groups called molecules. Powerful microscopes produce pictures of atoms and molecules. We cannot see them directly.

What is kinetic energy?

Atoms and molecules are in motion all the time. They have energy called kinetic energy.
“Kinetic” comes from a Greek word meaning to move.
In a solid object like a bar of iron, the atoms are packed close together.
When the iron bar is cold, they vibrate only a little.
When the iron bar is heated up, the atoms start to move faster and faster.
The quicker the atoms move, the more kinetic energy they have.
If the iron bar becomes hot enough, the atoms have so much kinetic energy that they can separate from each other.
Then the solid iron melts and becomes a liquid.