Presure is merely force over a defined area. Gas pressure is just the collective force of gas molecules running into a container wall. Since gas molecules have such small masses, these gas molecules are moving at very fast speeds.
The reason why these things do bounce off the walls and one another is because molecules and atoms have clouds of electrons around them that repel each other, positive repels positive and negative repels negative. So these things didn't have these repulsive electrostatic forces, they'd just run right through each other.
The reason why these things do bounce off the walls and one another is because molecules and atoms have clouds of electrons around them that repel each other, positive repels positive and negative repels negative. So these things didn't have these repulsive electrostatic forces, they'd just run right through each other.