How Do Simple Machines Make Work Easier? Six Machines for Kids

What You'll Learn

• The six classic simple machines are the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw.
• A lever tips on a fulcrum; placing the fulcrum close to the heavy load lets a small push on the long end lift it.
• An inclined plane (ramp) trades less force for more distance compared with lifting straight up.
• A wheel and axle turns a small force on the wide wheel into much more force on the narrow axle.
• A screw is an inclined plane wrapped in a spiral around a rod, trading many turns for extra pushing force.
• A single fixed pulley changes the direction of a pull but does not by itself reduce the force needed.

Words to Know

Simple machine

A tool with no motor that makes a push or pull easier

A seesaw, a ramp, a doorknob

Force

A push or a pull on something

Pushing a box, pulling a wagon

Lever

A bar that tips on a point (a fulcrum) to lift something with less push

A crowbar prying open a lid

Fulcrum

The spot a lever tips over, like the middle of a seesaw

The triangle block under a seesaw

Wheel and axle

A wheel attached to a rod so turning the wheel turns the rod easily

A doorknob, a steering wheel

Pulley

A wheel with a rope that changes which way you pull

A flagpole rope, a window blind

Inclined plane

A flat ramp that lets you push something up slowly instead of lifting it straight up

A loading ramp, a skateboard ramp

Wedge

Two ramps stuck back-to-back that push things apart

An axe blade, a doorstop

Screw

A ramp wrapped in a spiral around a pole

A jar lid, a lightbulb, a spiral slide

Mechanical advantage

How much easier a machine makes a job

A long ramp giving you a big mechanical advantage

Check What You Learned

Fun Facts

• There are six classic simple machines: the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw

  Source: Britannica, "simple machine"

• A ramp that is 4 times longer than it is tall lets you push something up it using roughly ¼ the force it would take to lift it straight up, ignoring friction — you trade less force for more distance

  Source: general physics of the inclined plane, mechanical-advantage principle

• A doorknob's wide knob and skinny rod are a wheel and axle — turning the wide knob a little distance with a little force turns the skinny rod with much MORE force (just a shorter distance), which is why a wide knob is so much easier to twist than the bare rod would be

  Source: Britannica, "wheel and axle"

• Scissors are two levers joined at a pivot (the fulcrum) working together — that's why they can cut with much less hand force than tearing with bare fingers

  Source: Britannica, "lever"

• A single pulley (like a flagpole pulley) does not reduce the force needed — it changes the DIRECTION of the pull, which is still useful

  Source: Britannica, "pulley"