Energy exists in many forms all around us. The development of our modern society has been accomplished because scientists and engineers have learned to capture some of that energy and transform it into ways to do useful work. The conversion of energy from a chunk of coal into steam and then into mechanical engines that could do heavy work was a critically important role of engineers in the 19th century that helped to start the industrial revolution. An engineer needs to know where to "find" energy resources and then how to convert them into forms that are more useful for all of the machines and gadgets we use in our daily lives.
The law of conservation of energy states: Energy can neither be created nor destroyed... But, it can be converted! (Relate back to the energy forms and energy flow diagrams discussed earlier. In some cases, the items had different starting and ending energy forms, so conversions were going on.) The truck was an example of chemical energy converted to mechanical and heat through the COMBUSTION of fuel.
Energy conversions are necessary when we desire a certain form or state of energy, perhaps heat for our homoes, when the only form available is different, perhaps chemical energy in fuel. Conversions are also useful for transporting energy to where it is needed. For example a hydropower plant may be miles from our homes, so how do we use its energy? We convert its mechanical energy (flowing water) to electric energy, which is easily transported to our home via wires, and then back to mechanical energy in our blenders.
(Next, conduct the combustion demo to illustrate how we can add conversion processes to our energy flow diagrams.)
In the first lesson, we saw that energy can be transformed from one form to another, and during this conversion, all the energy that we put into a device comes out. However, all the energy that we put in may not come out in the desired form.
For example, we put electrical energy into a bulb and the bulb produces light (which is the desired form of output from a bulb), but we also get heat from the bulb (undesired form of energy from an electric bulb).
Electrical energy conversion to light and heat.
Therefore, energy flow into and out of any energy conversion device can be summarized in the diagram below:
Energy Flow Diagram for an Energy Conversion Device
When all forms of energy coming out of an energy conversion device are added up, it will be equal to the energy that is put into a device. Energy output must be equal to the input. This means that energy can not be destroyed or created. It can only change its form.
In the case of an electric bulb, the electrical energy is converted to light and heat.
The amount of electrical energy put into a bulb = the amount of light energy (desirable form) plus the heat energy that comes out of the bulb (undesirable form).
Say you go to the mall with $100 and you come back with only $10. You need to account for the $90 that was spent. After thinking about it, you come up with the following list:
Gas ($15); Sandwich, fries, and a drink ($8); Lost ($5); New clothes ($62)
So you spent $62 on something useful - the clothes - but you spent additional money for other things that were necessary for your trip to the mall.
Instructions: Identify the useful energy output(s) and undesirable energy output(s) in the energy conversion devices below. Enter your answers in the fields provided, and click the "Check Answers" button to check your work. If you need help, click the yellow buttons marked with an "H" for a hint.