Week 5 Materials

Day 1

1. Is it possible to make a device that outputs more energy than you put into it?

NO

And if it were possible, Mark would use it to conquer the planet.

2. Some examples:
   1. a set of lightbulbs, connected in parallel. What happens to the brightness when you increase the number of bulbs? Why?
   2. The Shake Light flashlight -- it doesn't have a battery. Where is the energy coming from?
   3. The pull-back VW mini-bus. If you push it forward, it rolls to a stop in a couple of feet. If you pull it backward, then let go, it rolls a good 10 feet or more before it stops. Could Mark build a world domination device out of VW mini-bus pull-back cars? Why not?
   4. The lever. How much force does it take to lift a mass, if the mass is on one end of the lever and you are pulling on the other end? What if you move your pulling point halfway in toward the pivot point? What if you move the mass half way in toward the pivot point? What does it mean that one of these situations requires less force? Is this a device with which you could conquer the planet?

Day 2

1. Measuring the lever. Your task is to characterize how to use a lever by systematically changing where the pivot point is, where the load mass is, and where the applied pulling force is -- and measuring how much force you have to apply to "balance" it. Make sure to think carefully about all the possible arrangements of the mass, pivot, and applied force, and measure carefully.

Day 3

1. Discussion of principles of the lever. What is the implicit trade-off that explains why you can't use the lever to create infinite free energy? Examples of lever use.
2. The pulley. How can you arrange a pulley or pulleys to require the least possible force to lift a 1 kilogram mass?

Day 4

1. Quiz on potential and kinetic energy transitions; lever and pulley concepts.