Introduction to

Simple Machines

What are they?

Simple machines are machines with few or no moving parts that are used to make work easier

Types of Simple Machines Wedge Wheel and Axle Lever

Inclined Plane Screw


Wedge • Pushes materials apart, cuts things • Examples: axe, doorstop, chisel, nail, saw, jackhammer, bulldozer, snow plow, horse plow, zipper, scissors, airplane wing, knife, fork, bow of a boat or ship

The Wedge • A wedge is used to split, tighten, or secure a hold. • A wedge is usually a triangle shape with a sharp point. • If you apply force at one end, the wedge will go between something, in this case an ax splits a piece of wood.

Where can we find wedges? • Wedges that split: • Your teeth! • Every time you bite into something, you are using a wedge. • Wedges that cut: • A saw! • A knife!

• Wedges that tighten: • A doorstop to keep the door open. • Wedges that hold things together: • A nail holds wood to a wall or other wood.

Wheel and Axle • Makes it easy to move things by rolling them, and reducing friction • Examples: car, bicycle, office chair, wheel barrow, shopping cart, hand truck, roller skates

The Wheel and Axle • Two or more wheels are connected by an axle. • The wheel turns with or around the axle. • This car wheel has a big axle that it rotates around when the car moves.

Why do we need wheels? • Wheels help us move heavy objects. • They roll easily. • Did you know a doorknob is really two wheels connected by an axle? You can’t see the axle because it’s inside the wheels, but it’s there! • If there wasn’t an axle, the doorknob wouldn’t turn!

Another kind of wheel is called a gear! • A gear is a wheel with teeth. • The teeth fit in between each other and turn. • When one gear turns, its teeth push against the teeth of the other gear and they both turn. • There are gears on your bike, on a can opener and on an egg beater.

Lever • Makes lifting weight easier by using a fulcrum to redirect force over a longer distance • Examples: see-saw, dump truck, broom, crane arm, hammer claw, crow bar, fishing pole, screwdriver, bottle opener

Levers • There are three parts to a lever: • Load • Force • Fulcrum: support or balance

A seesaw is a lever • Let’s pretend you are riding a seesaw with your friend. • The center support is the fulcrum, which does not move. • The load is your friend sitting on one end. • You exert the force at the other end trying to lift your friend off the ground.

• When you push down on your seat, (the force) you can lift your friend (the load) while the fulcrum acts as the pivot point, making the seesaw go up and down. • It’s easy to lift your friend this way instead of just picking her or him up by yourself!

Inclined Plane • Makes it easier to move objects upward, but you have to go further horizontally • Examples: highway or sidewalk ramp, stairs, inclined conveyor belts, switchback roads or trails

The Inclined Plane • It is a slanted surface or ramp. • It makes moving objects easier. • Roads are also inclined planes. Instead of going straight up, like this: roads go up at small angles, like the picture.

Screw • • • •

Turns rotation into lengthwise movement Takes many twists to go a short distance Holds things together Examples: screws, bolts, clamps, jar lids, car jack, spinning stools, spiral staircases

The Screw • The three parts to a screw: • Head • Shaft • Tip • The head is the part that you exert a force on. • The shaft has ridges, called threads that wind around the screw. If it doesn’t have the threads, it is probably just a nail.

How to use a screw: • Fasten two things together • When you turn it, the threads cut a groove in the material, making a hole. The groove holds the screw tightly in place. • To remove the screw you turn it the opposite way, you can’t just pull it out.

Pulley • Makes lifting things with a rope easier by redirecting force and the addition of additional pulleys • Examples: flag pole, elevator, sails, fishing nets, clothes lines, cranes, window shades and blinds, rock climbing gear

Pulleys • Lifting a bucket full of water is a lot of work! • A pulley is a wheel with a rope running over it. The wheel has a groove, called a sheave, and it keeps the rope from slipping off the wheel. • Remember, since there is a wheel in a pulley there also has to be an axle! • These two men are using a pulley to help them lift their heavy bucket.

Why Use Simple Machines? For the mechanical advantage… • Making something easier to do, but it takes a little longer to do it • For example, going up a longer flight of stairs instead of going straight up a ladder

Complex Machines • Combining two or more simple machines to work together • Examples: – Car jack combines wedge and screw – Crane or tow truck combines lever and pulley – Wheel barrow combines wheel and axle with a lever

Summary Wedge

Pushes material apart, cuts

Wheel and Axle

Makes it easy to move things by rolling them, and reducing friction


Helps lift heavy weights using longer distances

Inclined Plane

Makes it easier to move objects upward; a longer path, but easier lifting


Turns rotation into lengthwise movement


Makes lifting heavy weights easier by redirecting force

Compound Machines • Compound machines consist of two or more simple machines put together. • Most devices are compound machines. • They can do more difficult jobs because their mechanical advantage is greater.

Name the Simple Machines Present in Each Compound Machine

Compound Machines

COMPOUND MACHINES • A compound machine is a combination of two or more simple machines that operate together.

COMPOUND MACHINES • Many familiar compound machines, such as a car, a washing machine, or a clock, are combinations of hundreds or thousands of simple machines.

Compound Machine Corkscrew • • • • •

Inclined Plane Wedge Screw Lever Wheel and Axle

Compound Machine Jack • • • •

Inclined Plane Wedge Screw Lever

A Wedge in a Compound Machine: Stapler • Staples are wedges: they cut through paper because their ends are pointed in a wedge shape. • Simple machines in a stapler: – Wedge – Lever

A Wedge in a Compound Machine: Scissors • The cutting edge of scissors is a wedge. • Simple machines in a pair of scissors: – Wedge – Lever