SIMPLE MACHINES

Work occurs when a force causes an object to move in the direction of the force. Work includes the force required to push or pull the object and the direction. Work = force x distance

Power is the rate at which work is done. How fast it happens. The more power the faster work is done.

Work & Power W = fd Object foRce Keep in mind direction more Power = faster wOrk hoW fast work is donE Rate

Machine A device that helps make work easier by changing the size or direction of a force. Do determine whether your machine changes compare work input (the work you do) with work output (the work by the machine).

Machines DO NOT SAVE work The amount of work stays the same; machines make them easier. There is a trade off between size of force or direction or both. Work = force x distance

Mechanical advantage A machine has a mechanical advantage if it multiples force. In other words, it allows you to use less force to do the same job.

Review True (1) or False (2): Work is a rate. Power is how fast work can be done. Machines save work. Work is only the amount of force needed to push or pull an object. Machines change the size and direction of a force. Mechanical Advantage makes you use more force to do the same job.

The six simple machines Levers Inclined planes (ramps) Wedges Screws Pulleys Wheel and axle

Levers Levers are simple machines consisting of a bar that pivots at a fulcrum (fixed point) Mechanical advantage depends on where the fulcrum is located.

Input Force vs Output Force Work Input = The force you put INto the machine Work Output = The force the machine puts OUT

Three types of levers The type of lever is determined by whether the fulcrum is located and where force is applied. These two variables (location of fulcrum and force application) determine whether the level changes direction, changes force or both!

First Class Lever First class – fulcrum between input and output First class levers change directions. If the fulcrum is closer to the load.

Second class lever – output force between fulcrum and input force Second class levers require little force for a larger distance.

Third class lever – input force is located between fulcrum and output force. Since more force is required to move the lever, mechanical advantage is less than one.

Inclined Planes (ramp) A simple machine which is a straight slanted surface. The longer the inclined plane, the greater the mechanical advantage. MA = length height

Wedges a double inclined plane that moves. A wedge has an edge or a point. It’s job is to drive itself into something by forcing itself into it. The longer and thinner a wedge is the greater the mechanical advantage (it takes less force).

Screws are inclined planes wrapped in a spiral. A screw applies a small force over a long distance. The closer the threads and the longer the screw, the greater the mechanical advantage.

Wheel & Axle is a simple machine consisting of two circular objects of different sizes. The mechanical advantage is determined by the radius, usually greater than one.

Pulleys are simple machines consisting of a grooved wheel that holds a rope or a cable. A load is attached to one end of the rope and the force applied to the other. The mechanical advantage is determined by the type of pulley.

Fixed pulley does move. The mechanical advantage is 1 since it’s only function is to change direction.

Movable Pulley are attached to the object that moves. They do provide a mechanical advantage since the force is applied over a greater distance.

Block and tackle includes a fixed pulley and a movable pulley to allow a large mechanical advantage when picking up heavy loads. The mechanical advantage is equal to the number of rope segments utilized.

Compound Machines Include more than one simple machine.

Review Is pushing a stroller work? (1) yes or (2) no Is doing homework work? (1) yes or (2) no Who is doing more work, (1) a guy who picks up a bag of groceries two feet or (2) a guy who picks up an identical bag of groceries four feet? Work is measured in (1) Newtons, (2) Joules or (3) Watts.

Review Power is (1) the amount of work you get done or (2) how fast you get work done Power is measured in (1) Joules, (2) Newtons or (3) Watts The person demonstrating the most power is the one who lifts 100 lbs over their head (1) in two seconds or (2) in four seconds. The person demonstrating the most power is the one who lifts 100 lbs over their head (1 three times in ten seconds or (2) four times in ten seconds

Simple Machines Machines lessen work. (1) True or (2) False Machines change (1) distance and force (2) direction and force or (3) distance and direction How many types of levers are there? What determines the amount of Mechanical Advantage? Machines can be more than 100% efficient (1) True or (2) False

What determines the mechanical advantage of: A wedge? A screw? A block and tackle pulley? What does a fixed pulley do (1) change force or (2) change direction? Which compound machines has the most simple machines (1) scissors, (2) can opener or (3) bicycle