Activities for Students
Activities for Teachers
Great AHS Engine
Several ideas are key to understanding how machines make work easier or peoples' efforts more powerful. Among them are the following:
- Energy is a fundamental property of everything in our universe. Some would say it is the fundamental property. One way to think about energy is to see it as distributed between these forms:
In many cases we design systems to change one type of energy into another. Hydroelectric generators tranform the gravitational potential energy of water held behind a dam into the kinetic energy of electrons flowing through wires.
- Work changes the energy of objects and systems. Work may change either the kinetic energy or the potential energy of an object or both. Often we use machines to do work. In many cases we think of work as the application of a force through a distance as in the example above of lifting a book from the floor to the desktop. The force applied was equal to the weight of (the force of gravity on) the book. The distance was the height of the desk.
Here Force X Distance = Weight X Height = Change in Potential Energy = Work.
- Power is how fast work is done or energy is used. Power lets us compare different ways of doing work to see which is quicker. For instance, a car engine with high horsepower will accelerate a car (change its kinetic energy) from 0 to 60 mph in less time than one with less horsepower.
- Efficiency measures how much of the energy we put into an engine or other system comes out as useful work. In every case some of the input energy is lost to heating the surroundings; nothing can be 100% efficient. What we call the "Laws of Thermodynamics" describe this relationship and limit people's quest for perpetual motion machines and "free" energy.