Liquid particles slide past one another and flow like gases. However, the difference between a liquid and a gas is that the particles of a liquid are more strongly attracted to each other than the particles in a gas. This attractive force between water molecules is called an intermolecular force. Because of intermolecular forces, liquid particles vibrate and spin in fixed positions while moving freely, but they do not have enough kinetic energy to overcome the intermolecular forces and become a gas. Kinetic energy is the energy an object has because of its motions. To overcome the intermolecular forces and become a gas, commonly called evaporation or vaporization, a liquid particle must have enough kinetic energy.