Unit+8

= Machines =

You are doing work when you use a force to cause motion. To measure the amount of work you do, multiply the force times the distance the object moved.
Work= F x D (work= force x distance the object moved)

Force (or weight) is measured in Newtons Distance is measured in meters.

Unit measure of work = Newton x meter or Newton meter A Newton meter (N-m) is called a joule (J)

Machines make work easier. The work that comes out of a machine can never be greater than the work put into a machine.

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In physics, power and energy do go hand in hand, but they're not the same thing. Whenever energy is changing or moving, there also is power, telling us how fast the energy is being transformed.

Energy is the property of matter that makes things happen. To make things happen, energy must change form or change locations. Power is a measure of how fast those energy changes are happening. Power is the rate of energy change per length of time. It tells us the quantity of energy that changed during a certain period of time. So the units of power are chunks of energy per amount of time, like 1 Joule per second (which is the same as 1 Watt), or 1000 Btu per hour, or 550 foot-pounds of energy per second (which is 1 horsepower). A 50 Watt light bulb converts 50 Joules of electrical energy to thermal energy and electromagnetic radiation (light) every second. A 100 Watt light bulb converts 100 Joules every second, mostly to heat and a little light also. Yes, it's true, a typical incandescent bulb is mostly making heat. That's why it's so hot to touch. Only about 2 percent of the electrical energy being converted in a light bulb becomes light. The other 98% is making heat that warms up the air in your house. Not so bad in the winter, but definitely unwanted on a hot summer day. [ [|Back to the Top] ]

machines
**Simple machines** are types of machines that do work with one movement. There are 6 simple machines; the inclined plane, the wedge, the screw, the lever, the pulley, and the wheel and axle.

Levers
The **lever** is a simple machine consisting of a bar supported at some stationary point along its length and used to overcome resistance at a second point by application of force at a third point. The stationary point of a lever is known as its **fulcrum**. There are three types of levers.

A first class lever is like a teeter-totter or see-saw. One end will lift an object (child) up just as far as the other end is pushed down. || A second class lever is like a wheel barrow. The long handles of a wheel barrow are really the long arms of a lever. || A third class lever is like a fishing pole. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish. ||
 * ** 1st Class Lever **
 * [[image:http://johnson.emcs.net/Physical/images/lever1.gif width="126" height="68"]] ||
 * [[image:http://johnson.emcs.net/Physical/images/lever1st.gif width="113" height="63"]] ||
 * [[image:http://johnson.emcs.net/Physical/images/actleverani.gif width="176" height="230"]] ||
 * ** 2nd Class Lever **
 * [[image:http://johnson.emcs.net/Physical/images/lever2.gif width="121" height="65"]] ||
 * [[image:http://johnson.emcs.net/Physical/images/lever2nd.gif width="130" height="72"]] ||
 * [[image:http://johnson.emcs.net/Physical/images/actlever2nd.gif width="229" height="135"]] ||
 * || ** 3rd Class Lever **
 * || [[image:http://johnson.emcs.net/Physical/images/lever3.gif width="125" height="84"]] ||
 * || [[image:http://johnson.emcs.net/Physical/images/leverthrd.gif width="77" height="83"]] ||
 * || [[image:http://johnson.emcs.net/Physical/images/actlever3ani.gif width="170" height="103"]] ||

Pulleys
A pulley is a simple machine made with a rope, belt or chain wrapped around a grooved wheel. A pulley works two ways. It can change the direction of a force or it can change the amount of force. A fixed pulley changes the direction of the applied force. A movable pulley is attached to the object you are moving. Fixed Pulley || Movable Pulley || Combined Pulley ||
 * [[image:http://johnson.emcs.net/Physical/images/pulyani.gif width="96" height="84"]] [[image:http://johnson.emcs.net/Physical/images/pulley.gif width="42" height="102"]] ||
 * [[image:http://johnson.emcs.net/Physical/images/actpull.gif width="164" height="253"]]
 * [[image:http://johnson.emcs.net/Physical/images/actpull.gif width="164" height="253"]]
 * [[image:http://johnson.emcs.net/Physical/images/pulley5.gif width="260" height="142"]] |||| [[image:http://johnson.emcs.net/Physical/images/crane.gif width="250" height="144"]] ||

Wheel and axles
A wheel and axle is a modification of a pulley. A wheel is fixed to a shaft. The wheel and shaft must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs.

Inclined Planes
The inclined plane is the simplest of simple machines because to make it work, nothing moves. You move! An example is a ramp which works by helping you lift things more easily up to a higher level. It can be really hard to carry something up a ladder. But carrying that same box up a staircase is an easier job, and carrying it up a smooth ramp is even easier.

Screws
A screw is a simple machine that is like an inclined plane. It is an inclined plane that wraps around a shaft.

Wedge
A wedge is a modification of an inclined plane that moves. It is made of two inclined planes put together. Instead of the resistance being moved up an inclined plane, the inclined plane moves the resistance.

**Mechanical Advantage**
Man first started using machines to make work easier and faster. How much easier and faster a machine makes your work is the mechanical advantage of that machine. In science terms, the mechanical advantage is the number of times a machine multiplies your effort force. To find the MA of a machine, you can divide the resistance force by the effort force. Most of the time the resistance force is the weight of the object in Newtons. MA = effort arm length / resistance arm length
 * To find the MA of a lever, divide the effort arm length by the resistance arm length.

To find the MA of an inclined plane, divide its length by its height. MA = length / height

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 * The MA of a pulley is equal to the number of supporting ropes.

Machines

 * Compound machines** are two or more simple machines working together. A wheelbarrow is an example of a complex machine that uses a lever and a wheel and axle. Machines of all types make work easier by changing the size or direction of an applied force. The amount of effort saved when using simple or complex machines is called mechanical advantage or MA. Make a compound machine in this [|game].

**Rube Goldberg Machines**
Rube Goldberg is actually a great cartoonist who drew to entertain America with his silly little machines. His actual name is Reuben Lucius Goldberg. Since most inventions are made to make difficult tasks simple, his inventions made simple look very complex. Rube Goldberg's cartoon contraptions were made complex to perform basic things. Today, these complex machines come to life. They are called the Rube Goldberg projects. Even a small funny idea can turn into something cool. Here is an example of one of his cartoons: Simplified pencil-sharpener: Open window (A) and fly kite (B). String (C) lifts small door (D) allowing moths (E) to escape and eat red flannel shirt (F). As weight of shirt becomes less, shoe (G) steps on switch (H) which heats electric iron (I) and burns hole in pants (J). Smoke (K) enters hole in tree (L), smoking out opossum (M) which jumps into basket (N), pulling rope (O) and lifting cage (P), allowing woodpecker (Q) to chew wood from pencil (R), exposing lead. Emergency knife (S) is always handy in case opossum or the woodpecker gets sick and can't work. [ [|Back to the Top] ]