The term work has a special meaning in science. Work is done only when a force moves an object. When you "push" or "pull" an object, you are doing work. Your force is acting on the object, causing it to move a certain distance, and that is the definition of work. Work=Force X Distance. Force is measured in newtons, distance is measured in meters, so the unit newton-meter or joule (J) is the standard unit of work. Power is like work, it simply tells you how fast work is occuring. The formula for power is work / time, and the standard unit is the watt (W). A machine is a device that makes work easier. Machines take a force (work input), and multiplies that force (work output). A machine does not increase the amount of work done, it simply makes the job easier by taking the force you apply and increasing it. The number of times a machine multiplies your effort is called the mechanical advantage of the machine, and MA must always be greater than 1. Another term known as efficiency is sometimes used to describe how helpful the machine is.

Either way you say it, levers work the same way. All levers have 4 parts, or 4 things we can find on them. The fulcrum-"full-krum", the load (resistance), the effort and of course the lever (stiff bar), itself. The fulcrum is the place a lever rocks back and forth. You could call it a pivot. When it's right in the middle of the lever, the amount of effort you push down equals exactly the amount of load you can lift with the other end. Pound a nail almost all the way into some wood. Use your fingers to pull it out. Now try pulling it out with the hammer. It's a lot easier. The claw on a hammer is a lever. We call this kind of lever a first-class lever. It does not mean it's a better lever - just that it's the first kind of lever. A first class lever has the fulcrum between the load and the effort. Use your first finger and thumb to pop off a metal cap from a soda bottle. Don't twist it off, pry it off. Now try a bottle opener. Much easier, right? A bottle opener is a second-class lever, which means the fulcrum is at the end of the lever and the load is in the middle. A third-class lever has its fulcrum at one end and the load at the other end, with the work you do in the middle. It's how a fishing pole works. You lift just a short distance at the handle, but the end of the pole pops up several feet - hopefully with dinner on the line.

A plane is a flat surface. For example, a smooth board is a plane. Now, if the plane is lying flat on the ground, it isn't likely to help you do work. However, when that plane is inclined, or slanted, it can help you move objects across distances. And, that's work! A common inclined plane is a ramp. Lifting a heavy box onto a loading dock is much easier if you slide the box up a ramp--a simple machine.

A wedge is made up of two inclined planes back to back. Wedges are designed to separate objects. Look at the diagram, the design of a ship takes the form of a wedge. You find a wedge on an axe, or a knife.

Wedges can be used in several ways:

• Wedges can help you grip things to be lifted. Pushing one under an object provides a space for your fingers. The longer the wedge and the smaller the angle of slope, the less the force needed, but the wedge must be pushed in a greater distance.
• Wedges can also be used to tighten or hold things in place, for example, a wedge peg to hold a bench together, or a doorstop.
• Wedges are mostly used to push things apart, for example, pounding a nail into a block of wood. Other examples are a chisel, cutting tools, an axe (also a lever), a can opener (also a lever), plow blade, and the bow of a boat or ship.
• The purpose or advantage of the wedge is to change the direction of the applied force. When the force is applied downward on a wedge, it is able to push outward in two directions.

Now, take an inclined plane and wrap it around a cylinder. Its sharp edge becomes another simple tool: the screw. Put a metal screw beside a ramp and it's kind of hard to see the similarities, but the screw is actually just another kind of inclined plane.A screw, like a wedge, is another form of an inclined plane. A screw is an inclined plane wrapped around a cylinder to form a spiral.

A wheel and axle is a lever that rotates in a circle around a center point or fulcrum. The larger wheel (or outside) rotates around the smaller wheel (axle). Bicycle wheels, ferris wheels and gears are all examples of a wheel and axle. Wheels can also have a solid shaft with the center core as the axle such as a screwdriver or drill bit. The wheel, the round end, turns the axle with greater force causing movement. On a wagon, for example, the bucket rests on top of the axle. As the wheel rotates the axle, the wagon moves. Now, place your pet dog in the bucket, and you can easily move him around the yard. On a truck, for example, the cargo rests on top of several axles. As the wheels rotate the axles, the truck moves.

Instead of an axle, the wheel could also rotate a rope or cord. This variation of the wheel and axle is the pulley. In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's rotation to raise and lower objects. On a flagpole, for example, a rope is attached to a pulley. On the rope, there are usually two hooks. The cord rotates around the pulley and lowers the hooks where you can attach the flag. Then, rotate the cord and the flag raises high on the pole. Look at the diagram below.

If two or more simple machines work together as one, they form a compound machine. Most of the machines we use today are compound machines, created by combining several simple machines.

1. Online Practice Test
2. Interactive Tutor

Student objectives will include the ability to:
1. distinguish work's relationship with energy
2. describe power
3. define work in terms of force and distance
4. identify six simple machines and their function.