Machines Simple Machines Have few or no moving

Machines

Simple Machines • Have few or no moving parts • Make work easier • Can be combined to create complex machines • Six simple machines: Lever, Inclined Plane, Wheel and Axle, Screw, Wedge, Pulley

Machines • Make work easier by: 1) decreasing force by increasing distance 2) increasing force by decreasing distance 3) force and distance stay the same but the direction is different.

Machines Make Work Easier by:

Mechanical Advantage • We know that a machine multiplies whatever force you put into it: - Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead of stairs • The amount that the machine multiplies that force is the mechanical advantage of the machine • Abbreviated MA

Mechanical Advantage • (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere • (AMA) Actual MA: This is simply the MA of a machine in the world as we know it - Force is lost due to friction - Force is lost due to wind, etc. • Can we have an ideal machine?

Mechanical Advantage MA = output force input force IMA = input distance output distance Ø Mechanical advantage is a ratio so there is no unit.

Efficiency • The efficiency is a ratio that measures how much work the machine produces versus how much work goes in • Example: We have an inclined plane with an ideal MA of 3. We measure our real-life inclined plane and find an MA of 2. Efficiency = Actual MA/Ideal MA x 100% = (2/3) X 100% = 66. 66%

Inclined Planes • A slope or ramp that goes from a lower to higher level • Makes work easier by taking less force to lift something a certain distance • Trade off: the distance the load must be moved would be greater than simply lifting it straight up

Mechanical Advantage: Inclined Plane • The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope • So for our plane MA = 15 feet/3 feet = 5 • Let’s say S = 15 feet, H = 3 feet

Wedge • An inclined plane on its side • Used to cut or force material apart • Often used to split lumber, hold cars in place, or hold materials together (nails)

Mechanical Advantage: Wedge • Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end • So for our wedge, MA = 6”/2” = 3 • They are one of the least efficient simple machines

Screw • An inclined plane wrapped around a rod or cylinder • Used to lift materials or bind things together

Mechanical Advantage: Screw • The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw • The pitch of the screw is the number of threads per inch • So for our screwdriver MA = 3. 14”/0. 1” = 31. 4 Circumference = ∏ x 1” = 3. 14” Pitch = 1/10” = 0. 1”

Wheel and Axle • A larger circular wheel affixed to a smaller rigid rod at its center • Used to translate force across horizontal distances (wheels on a wagon) or to make rotations easier (a doorknob) • Trade off: the wheel must be rotated through a greater distance than the axle

Mechanical Advantage: Wheel and Axle • The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle • So for our wheel and axle MA = 10”/2” = 5

Pulley • A rope or chain free to turn around a suspended wheel • By pulling down on the rope, a load can be lifted with less force • Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

Mechanical Advantage: Pulley • The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley • So for the pulley system shown there are 3 ropes supporting the bottom pulley MA = 3 • This means that if you pull with a force of 20 pounds you will lift an object weighing 60 pounds

Lever • A rigid board or rod combined with a fulcrum and effort • By varying position of load and fulcrum, load can be lifted or moved with less force • Trade off: must move lever large distance to move load small distance • There are 3 types of levers

st 1 Class Lever • The fulcrum is located between the effort and the load • Direction of force always changes • Examples are scissors, pliers, and crowbars

2 nd Class Lever • The resistance is located between the fulcrum and the effort • Direction of force does not change • Examples include bottle openers and wheelbarrows

3 rd Class Lever • The effort is located between the fulcrum and the resistance • Direction of force does not change, but a gain in speed always happens • Examples include ice tongs, tweezers and shovels

Mechanical Advantage: Lever • The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load • For our example, MA = 10/5 = 2 • Distance from effort to fulcrum: 10 feet • Distance from load to fulcrum: 5 feet

The trick is WORK • Simple machines change the amount of force needed, but they do not change the amount of work done • What is work? • Work equals force times distance • W=Fxd • By increasing the distance, you can decrease the force and still do the same amount of work

Examples: • Inclined Plane: • Lever: • Work is equal on both sides of a lever. You move the long end a LARGE distance with SMALL force. The other end moves a SMALL distance with a LARGE force, which is why it can lift heavy objects. • It takes a certain amount of work to get the cabinet into the truck. You can either exert a LARGE force to lift it the SMALL distance into the truck, or you can exert a SMALL force to move it a LARGE distance along the ramp.