Why do neither liquids or gases have permanent shapes?

A gas and a liquid will change shape to fit the shape of their container.

Explanation:

Solid - In a solid, the attractive forces keep the particles together tightly enough so that the particles do not move past each other. Their vibration is related to their kinetic energy. In the solid the particles vibrate in place.

Liquid - In a liquid, particles will flow or glide over one another, but stay toward the bottom of the container. The attractive forces between particles are strong enough to hold a specific volume but not strong enough to keep the molecules sliding over each other.

Gas - In a gas, particles are in continual straight-line motion. The kinetic energy of the molecule is greater than the attractive force between them, thus they are much farther apart and move freely of each other. In most cases, there are essentially no attractive forces between particles. This means that a gas has nothing to hold a specific shape or volume.

Conclusion: There are following reasons due to this gases and liquid have not permanent shape

1) Particle have large distance between them

2) Weaker Inter-molecular energy as compare to solid

3) Greater K. E as compare to solid