Finish the activities you started on Monday with the pulley systems. See previous blogpost.

In your notebooks, write a summary relating what you have learned about the effects different arrangements of pulleys have on forces and work. Take pictures to support your thinking.

Remember that we have begun our definition of energy by saying that “energy is what is required to do work” and that the amount of work done can be found by multiplying the force applied to an object time the distance the force has been applied. The unit of work then is ** Newton-meter **which is equal to the unit of energy called

*. You can explore the various forms of energy through the units and formulas. For example, gravitational potential energy of an object lifted above the ground would be weight x height (above the ground). Remember that weight is a force which is acceleration x mass. So gravitational potential energy would be mgH (the mass x the acceleration due to gravity x the height above the ground). The formula for kinetic energy is*

**Joule****KE = 0.5 • m • v**where

^{2 }**m**= mass of object

**v**= speed of object. What else do you see in these inter-related ideas about energy and work? Investigate the history of these ideas. Newton had a feeling for energy but he thought energy was something like momentum (mv). Scientists who came after Newton (using the mathematics Newton invented–the calculus) derived the concepts we use today. These scientists also related heat to energy. The story of these discoveries is truly fascinating. Highly recommended is the Story of Science by Joy Hakim (http://www.joyhakim.com/)

Games with simple machines

http://www.msichicago.org/fileadmin/Activities/Games/simple_machines/

There are many websites and references on simple machines. Here are two:

**Leonardo da Vinci’s Inventor’s Toolbox –**

**The Essence of Simple Machines **

Build and analyze simple machines from the K-Nex kits. Record your observations and thoughts in your notes. Take pictures to support your analysis.

Simple machines can:

1. Change the direction of a force.

2. “Spread out” the effort (force).

Simple machines cannot reduce the total about of work. This is connected to the idea of the Law of Conservation of Energy (see links in the introductory blog post about energy).

Traditionally, six classes of simple machines have been described: http://physics.about.com/od/physicsintherealworld/p/simplemachines.htm

Lever, Wheel and axle, Inclined plane, Wedge, Screw, Pulley

Why do you think there are only 6? Do you think there are others? Would you consider the wedge a double inclined plane? What about a screw–could this be a twisted inclined plane?