There are many other forms of energy, such as electrical, gravitational, nuclear, and strain energy. An example is a lump of coal, which when burned will release a certain number of joules of energy. Another example is food. A calorie contains almost 4.2 joules of energy, so if we eat a piece of chocolate that has 100 calories we can expect to get around 420 joules of energy from it. Energy used up over time.
Most electrical devices have their power consumption rated in watts.
A watt is a rate of energy consumption of one joule per second. So, if you have a light bulb in your room that is rated at 100W it is using energy at a rate of 100 joules every second. To go back to the example in the previous bullet point, a piece of chocolate with 100 calories isn t very big but could easily ruin a planned daily diet. Personally, I d rather eat the chocolate. So, to summarise, energy can come in many forms, it can be transferred from one system to another.