Conservation of Energy Energy Transformation

Law of Conservation of Energy Conservation of energy refers to the fact that energy cannot be created or destroyed. The total amount of energy in the universe stays the same. Energy can only change forms, but it can never just cease to exist.

Law of Conservation Scientists and texts will often make the statement that “energy is conserved”. That just means that the TOTAL energy of the object or in the system stays the same. The total energy is just all the different type of energy added up. So one type of energy may turn into another type while an object changes position or temperature. This is usually referred to as energy transformations. These multiple types will always combine to the same total.

Energy Transformation A pendulum is one of the simplest examples of energy conservation. At the left most position the pendulum bob has only gravitational potential energy. It’s actually not moving for a split second here so it has no kinetic energy. But then gravity causes it to fall, which means it starts moving. So now it has kinetic energy. But that energy had to come from somewhere. It cannot be created. At the same time the gravitational potential energy is decreasing because the height is going down. But this energy had to go somewhere, it cannot be destroyed. Turns out this problem is solved if we assume that the potential energy is turning into the kinetic energy.

Energy Transformation cont. And at the lowest point all the gravitational potential that can transform has transformed into kinetic energy. So the lowest point is where the bob moves the fastest. As the bob moves back up the opposite process happens. Gravity is pulling it down so the object slows and loses kinetic energy. That kinetic energy is being used to get higher which means it is being turned into gravitational potential energy. And then it falls back down and the cycle repeats. Conservation of energy means that the total energy has the to stay the same. So if you add up the kinetic and potential energy at any one point you should always get the same number.

Energy Transformation cont. Now, normally you don’t want to have to write out or read that long of an explanation about energy changing forms and it is more efficient to just draw a picture or a flow chart. For our pendulum that would look something like this: And so forth. To draw a energy transformation diagram you just have to ask yourself: What kind of energy is it starting with? And what is happening to that energy as it moves/changes? GPE KE GPE

Energy Transformation cont. This situation is slightly more complicated than this. Under the Law of Conservation of Energy, you might assume this pendulum cannot lose energy. But if you observe it, you will notice that it won’t keep going as high. It will slow down and eventually it will stop suggesting it doesn’t have as much energy anymore. But we also know that energy cannot be destroyed so where is this energy going? It’s going in the air. The pendulum bob is colliding with air molecules and making them move faster which causes them to heat up. So even though the bob lost energy itself, the energy was not destroyed. It just turned into thermal energy and went into the environment. GPE KE GPE Thermal Thermal Thermal

Another Example When drawing your own diagrams you don’t necessarily need to go into as much detail. You just need to ask yourself what kind of energy is the object starting with? And what kind of energy do I want to get out of it? Example: Using an ipod to listen to music. -The ipod is powered by a battery which is storing chemical potential energy. -The point of the ipod is to play music which is vibrational energy (sound). -There is a step in between these two if you want to include it (but don’t have to). The battery actually turns chemical potential energy into electric energy, which is then converted into a sound wave that you can hear. But also as the electrons move through the wire, it produces heat. So a more complete energy transformation diagram might look like: Chemical PE Vibrational Energy Chemical PE Electric Energy Vibrational Energy Thermal