Chapter 5.2 Using Machines

What is a machine? Definition: A machine is a device that makes doing work easier. It does this by increasing the force that can be applied to an object. Most people think of machines as power equipment like the crane to the right.

Machines DO NOT create energy In an ideal situation (meaning without friction), the energy put out by the machine to do the work would equal the energy put in. However, due to heat loss associated with friction, this NEVER happens! The energy of burning coal to move this steam train is greater than the energy converted to the tracks for motion. Why? A lot of the energy is lost to heat in the engine as well as to overcoming the friction of the wheels on the track. Wind resistance is another source of energy lost!

Simple Machines: Remember that: W = f*d Therefore, Definition: A Simple Machine is a machine that does work using only one movement. Simple Machines have been used by people for a very long time to make doing work less forceful. The principle of a Simple Machine is: “Apply a small force over a large distance to get a large force over a small distance.” Remember that: W = f*d Therefore, f*d = f*d You apply a smaller force over a greater distance to get a LOT of force over a small distance.

Mechanical Advantage The ideal mechanical advantage (IMA) of a machine is the number of times a machine multiplies the effort force(Feffort) to overcome the resistance force(Fresistance): IMA = de/dr = .30m/.05m = 6 Actual MA = Fr/Fe = 1500N/300N = 5 Fe = 300N de = .30 m Fr = 1500N dr = .05 m

Even Simple Machines are NOT 100% efficient All these simple machines make doing work easier, but all require MORE work put INTO (Win) them than the work OUT (Wout) needed to do a job.

Calculating machine efficiency The efficiency of a machine is calculated by the dividing the work put out (Wout) by the machine to do the work divided by the work put into the machine to do the job times 100%. Efficiency = (Wout/Win) x 100% Note: The efficiency of a machine is NEVER 100%

Though six Simple Machines are mentioned, they actually fall under two categories: The Lever The Inclined Plane Pulley Wheel & Axle Screw Wedge

There are three types of levers Resistance Force Fulcrum Fulcrum Fulcrum

Examples of Levers 1st class lever: Resistance Force Effort force Fulcrum

Levers continued: 2nd Class lever: Effort force Resistance Force Fulcrum

Levers continued: 3rd Class lever: Effort force Fulcrum Resistance Force