SIMPLE MACHINESBy:

Drew Harris

Simple machinesThe basic machines that make up other

machines are called simple machines. There are six of them. They are lever, pulley, wheel and axle, inclined plane, screw, and wedge. All these machines help us move things by changing the size of the force applied, the direction of the force, or both at once. 

LeverOne simple machine is a lever. A lever is made up of a bar that turns on a fixed point. The fixed point, or point that doesn’t move, is called the fulcrum.When you push or pull a lever, you put a force, called the effort force, on one side of the bar. This force can be used for any simple machine. Effort force causes the bar to turn on the fulcrum. The other end of the bar moves. The resulting force on that end is what you use to move a load, or do work.

Levers

The kind of lever shown above changes the direction of the force applied to it. A force down on one side pushes the other side up. On a seesaw the weight of a person on the high end pushes that end down. This lifts the person sitting on the other end.

When the fulcrum of this kind of lever is not in the middle of the bar, a light weight on the long side can balance a heavy weight on the short side.

On a seesaw you can balance a heavier person if the fulcrum is closer to him or her. Your smaller weight is on the long side of the lever. It balances the larger weight on the other end.

Levers

Pry barMany hand tools are levers. A pry bar is a lever that has a long handle and a short end for prying. A small force on handle becomes a much greater force on the prying end.

Sewing ScissorsSewing scissors have long, wedge-

shaped blades and short handles. The fulcrum is the bolt in the middle. A large movement of the handles causes a small movement of the blades to close the bolt.

Fingernail scissors have long handles and short blades. They make it easier to cut hard fingernails.

Fingernail Scissors

WorkMachines are used to do work. In science, the word work has a special meaning. Work is done on an object when a force moves the object through a distance.The force and motion must be in the same direction. By this definition, thinking isn’t work. Just holding a book isn’t doing work. But lifting a book is doing on the book. Carrying a basketball isn’t doing work on the basketball. This is because the force holding the ball up and its motion aren’t in the same direction. Shooting the basketball, however, is doing work on the basketball.

Measuring WorkWork can be measured and described

mathematically. To find the work done on an object, multiply the force used to move the object by the distance the object moves.

Work = force x distance Examples:Work = 10 N x 2 mWork = 20 N – m (Newton-meters)

PulleysA pulley is made up of a rope or chain

and a wheel around which the rope fits. When you pull down on one rope end, the wheel turns and the other rope end moves up. 

A pulley that stays in one place is called a fixed pulley. Fixed pulleys are often used to raise and lower something lightweight, such as a flag or a small sail, while you stay on the ground or the deck.

A fixed pulley is like a lever that has its fulcrum in the middle. Both the lever and the pulley change only the direction of the effort force. They do not change the size of the effort force.

Fixed Pulleys

Moveable pulleysA different kind of pulley can change the size of the effort force. This pulley is called a moveable pulley because it is free to move up and down. One end of its rope is tied down. The load is hooked to the pulley. Pulling up on the rope makes both the pulley and the load rise.A moveable pulley doesn’t change the direction of the effort. A pull up on the rope also pulls up on the land. But a moveable pulley does increase the resulting force. To lift a load of 50 Newtons, you need to pull with only a 25-newton force. As with a lever, you don’t get more work out of a moveable pulley than you put in it. It doubles your lifting force, but you pull twice as far. To lift a load 2 meters, you must pull up 4 meters of rope.

Pulley SystemsPulleys can be put together to make pulley systems, a form of compound machines. For example, you can use a fixed pulley with a moveable pulley. The moveable pulley increases your force. The fixed pulley changes the direction of your force.Adding more moveable pulleys to a system increases your force even more. Each moveable pulley you add also increases the length of rope you must pull to lift a load.

Pulley System

Wheel and Axle

Wheels and AxlesA wheel and axle is another simple machine that can make a job easier. A wheel and axle is made up of a large wheel attached to a smaller wheel or rod. A doorknob is part of a wheel and axle. The large round knob turns a smaller axle. The axle is what pulls in the latch to open the door. Without the large knob, it would be difficult to turn the axle. The small effort force you use to turn the knob becomes a large resulting force put out by the axle.As with other simple machines, you can get more work out of a wheel and axle than you put in it. Effort force is made larger. But the distance the outside of the knob turns is larger than the distance the axle moves.

Inclined PlanesAn inclined plane is a sloping

surface, such as a ramp, used to lift heavy loads with little effort. The inclined plane does not move. It works by allowing less force but over a greater distance.

ScrewA screw is an inclined plane

wrapped around a cylinder. The threads of a screw form a tiny "ramp" that goes around the screw. A screw allows you to use less force, and it changes the direction of the force.

WedgeA wedge is an inclined plane that tapers to a sharp edge. A wedge is really two inclined planes joined back to back. A wedge changes the direction of the force that a wedge moves.

Simple Machines Vocabulary

*simple machine – one of the basic machines that make up other machines*lever – a simple machine made up of a bar that turns on a fixed point*fulcrum – the fixed point, or point that doesn’t move, on a lever*effort force – the force put on one part of a simple machine, for example, when you push or pull on a lever *work – that which is done on an object when a force moves the object through a distance

Simple Machines Vocabulary*pulley – a simple machine made up of a rope or

chain and a wheel around which the rope or chain fits  *wheel and axle – a simple machine made up of a large wheel attached to a smaller wheel or rod  *inclined plane – a flat surface with one end higher than the other  *efficiency – how well a machine changes effort into

useful work  *screw – an inclined plane wrapped around a pole  *wedge – a machine made up of two inclined planes

placed back-to-back

Simple Machines WHAT IT IS HOW IT HELPS US WORK

EXAMPLES

LEVER A stiff bar that rests on a support called a fulcrum

Lifts or moves loads

Shovel, nutcracker, seesaw,crowbar,elbow,tweezers,bottle opener

INCLINED PLANE

A slanting surface connecting a lower level to a higher level

Things move up or down it

Slide, stairs, ramp, escalator, slope

WHEEL AND AXLE

A wheel with a rod, called an axle, through its center: both parts move together

Lifts or moves loads

Car, wagon, doorknob, pencil sharpener, bike

SCREW An inclined plane wrapped around a pole

Holds things together or lifts

Screw, jar lid, vise, bolt, drill, corkscrew

PULLEY A grooved wheel with a rope or cable around it

Moves things up, down, or across

Curtain rod, tow truck, mini-blind, flag pole, crane

WEDGE An object with at least one slanting side ending in a sharp edge

Cuts or spreads an object apart

Knife, pin, nail, chisel, ax, snowplow, front of a boat

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