Living things get energy through photosynthesis and metabolism. Photosynthesis is the conversion of light from the Sun into chemical energy. Metabolism is the process of converting energy from a stored form into other forms. Living things do metabolism, but for those that cannot photosynthesize, it is the only way to get useable energy. The energy from photosynthesis and metabolism can be use to do work. All forms of life show metabolic activities; they extract and transform energy from their environment and use it for maintaining life processes, growth, movement and reproduction.
Energy is also needed by non-living things. For example, when a person throws a ball, kinetic energy is required for the ball to move. The ball gets this kinetic energy from the person throwing it. The ball uses this kinetic energy to move through the air. Without the kinetic energy provided by the person throwing the ball, the ball would fall to the ground immediately.
When we heat a liquid, it will have more energy. The heat energy is used to overcome the forces of attraction between the molecules in the liquid. When the bonding between water molecules breaks up, the water will boil. A solid can melt into a liquid if heat is added. When a substance melts, some of the bonds holding the particles together are broken or loosened so that the particles can move freely around each other but are still close together. If enough heat is absorbed, the attraction between the molecules will no longer be able to hold them together and the solid will melt. The reason that energy has to be put into a substance to make it melt or boil is because the attraction between molecules needs to be broken.