Energy From the Sun

Almost all the energy used on Earth comes from the sun as light or heat. Plants use sunlight and water to make food during photosynthesis. Some animals eat these plants, while others eat the animals that eat the plants. Either way, all food contains stored energy that is transferred from the sun to plants, then to animals in the food chain. Animals break down food chemically and mix it with oxygen to produce the energy they need. The energy in food is measured in calories. In a calorimeter, a sample of food is burned inside a sealed container that captures the heat released and uses it to heat a known amount of water. The water temperature before and after heating is recorded. The difference is used to calculate the calories of heat energy released by the food. If calories in the body are not used, they become fat. We also obtain energy from fossil fuels that were formed over millions of years. Some of the sun’s energy soaked up by plants in prehistoric times changed form and became natural gas, which we collect and use to power things such as cars.