What are some types of energy?

Everyday objects are composed of atoms and molecules, which to some degree, are like billiard balls that are constantly bouncing off one another. "Mechanical energy" might include the kinetic energy of these particles, or potential energy stored in the physical arrangement. For example, a compressed solid exerts pressure because electromagnetic forces between particles tend to push them apart. Compressing a solid (moving the particles "uphill" against repulsive electromagnetic forces) stores potential energy in a similar way that pushing a boulder up a hill does (moving the object uphill against the attractive gravitational force of the Earth). On the other hand, a compressed gas exerts pressure because independently moving particles collide with the walls of the container and change direction. The particle is accelerated (its velocity vector changed), and the acceleration times the mass of the particle gives the force applied. Compressing a gas changes the average kinetic energy of the particles, which is reflected in the corresponding increase in the temperature of the gas. The pressure also increases, but this is because the same number of particles have been forced into a smaller volume, so they collide more often with the walls. The force of any given collision is the same, but the number of collisions has increased.