Why a solid keeps its shape

The idea

Solids have a definite shape and volume because their particles are tightly packed and held in fixed positions by very strong attractions; the particles only vibrate about their positions and cannot move past each other.

A stone in a bowl

A stone is put in a glass, then in a bowl, then on a plate.

What happens to the shape of the stone?

• It stays the same
• It takes the shape of each container
• It spreads out to fill each container

Move the solid

Put the stone into each container. Watch its shape, and its particles on the right.

The solid state

Solids have a definite shape and volume. Their particles are tightly packed, and very strong attractions hold them in fixed positions. The particles only vibrate (move to and fro) about their positions and cannot move past each other.

• What we see | Why (particles)
• Same shape and volume in any container | Tightly packed, held by very strong attractions
• The shape does not flow or change | Particles cannot move past each other
• Particles are never still | They vibrate about their fixed positions

Notes

Solids have a definite shape and volume: particles tightly packed, held in fixed positions by very strong attractions. They only vibrate and cannot move past each other.

Check yourself

Why does a stone keep its shape in any container?

How do the particles of a solid move?

Which is true for a solid?

• Its particles do not move at all. They do move: they vibrate about their fixed positions.
• Very strong attractions hold its particles in fixed positions — correct. Yes. The particles cannot move past each other.
• The containers are too small. The stone keeps its shape in big and small containers alike.
• They slide past each other. Particles of a solid cannot move past each other.
• They move freely in all directions. That is how the particles of a gas move.
• They vibrate about their fixed positions — correct. Yes. They move to and fro but stay in place.
• It has a definite shape and a definite volume — correct. Yes. Its particles are tightly packed in fixed positions.
• It has a definite volume but no definite shape. That describes a liquid.
• It has neither a definite shape nor a definite volume. That describes a gas.