Tools and simple machines

by Chris Woodford. Last updated: January 12, 2022.

It's built to last you a lifetime—quite literally. But though the human body is the most amazing tool at your disposal, it often needs a helping hand. Tools made from metal, wood, and plastic work like extensions of your body, making you feel stronger and helping you work faster and more efficiently. In science, tools like this are called simple machines. And although you might think there's a big difference between a tiny little wrench and a huge great earthmover, exactly the same physics is at work in both. Let's take a closer look at tools and machines and how they work!

Photo: This hydraulic digger uses a collection of simple machines (wheels, axles, and levers) to magnify the force its driver can exert. How many different machines you can spot at work inside the digger? Here are a few to start you off: the levers the driver pulls to make it do things, the wheels, the lever arm with the bucket on the end... and there are plenty more!

What is a machine?

To do anything at all—to lift a box, to push a car, to get out of bed, to jump in the air, to brush your teeth—you need to use a pushing or pulling action called a force. If you go around telling people you're strong, what you really mean is that your body can apply a lot of force. You may have watched incredibly strong people on TV pulling trucks or trains with their bare hands, but there's a limit to what even the most muscle-bound human body can do. Simple machines let us go beyond that limit. Simple machines can make us all strong!

Photo: Thumbtacks (sometimes called drawing pins) are a bit like nails with built-in hammers. When you push on the large, flattened head, the force you apply (to the large flattened end) is effectively magnified because it's concentrated into a much smaller area at the tiny pin head. According to science, even thumbtacks are simple machines.

When you hear the word "machine", you probably think of something like a bulldozer or a steam locomotive. But in science, a machine is anything that makes a force bigger. So a hammer is a machine. A knife and fork are a pair of machines. And even an egg whisk is a machine. All these machines have one thing in common: when you apply a force to them, they increase its size and apply a greater force somewhere else. You can't cut meat with your hand alone, but if you push down on a knife, the long handle and the sharpened blade magnify the force you apply with your hand—and the meat slices effortlessly. When you pound a nail with a hammer, the handle increases the force you apply. And because the head of the hammer is bigger than the head of the nail, the force you apply is exerted over a smaller area with much greater pressure—and the nail easily enters the wood. Try pushing in a nail with your finger and you'll appreciate the advantage a hammer gives you.

There are five main types of simple machine: levers, wheels and axles (which count as one), pulleys, ramps and wedges (which also count as one), and screws. Let's look at them more closely.

Levers

A lever is the simplest machine of all: it's just a long bar that helps you exert a bigger force when you turn it. When you sit on a see-saw, you've probably figured out that you need to sit further from the balance point (known as the pivot point or fulcrum) if the person at the opposite end is heavier than you. The further away from the fulcrum you sit, the more you can multiply the force of your weight. If you sit a long way from the fulcrum, you can even lift a much heavier person sitting at the other end—providing they sit very close to the fulcrum on their side. The force you apply with your weight is called the effort. Thanks to the fulcrum, it produces a bigger force to lift the load (the weight of the other person). The words "effort" and "load" can be very confusing, so we've avoided using them in this article. The important thing to remember about levers is that the force you produce is bigger than the force you apply:

With a long lever, you can exert a lot of leverage. When you use an axe or a wrench, the long handle helps to magnify the force you can apply. The longer the handle, the more leverage you get. So a long-handled wrench is always easier to use than a short-handled one. And if you can't budge a nut or bolt with a short wrench, try one with a longer handle.

Photo: Two tools that are levers. Left: A garden fulcrum weeder (green, top) and a pipe wrench (red, bottom). The weeder is a class-1 lever, while the wrench is a class-2 lever (these terms are explained immediately below). Right: Here's the weeder in action. The built-in fulcrum makes it easy to lift weeds with a long, strong tap root.

Wheels and axles

The invention of the wheel and axle (the rod around which a wheel turns), around 5500 years ago in the Middle East, revolutionized transportation and gradually brought huge changes to society, but what made it so special? It's easier to push a cart loaded with a heavy box than to push the same box along the ground because the cart's wheels and axles reduce friction and provide leverage. You can find out how in our main article on how wheels work.

Big wheels are used to multiply force in other ways too. Pipes, for example, have wheels called stopcocks (or stop valves) fitted to them. When you turn the outer rim of a stopcock, the inner axle turns with much greater force—so the pipe is easier to close. Steering wheels work this way too. A truck or a bus often has a bigger steering wheel than a car, because it takes more force to turn its wheels. The bigger wheel gives the driver more leverage.

Wheels can multiply distance and speed as well as force. Bicycles have large wheels so they go faster. When you pedal, you power the inside of the wheel. But the wheel's outer rim turns around faster and covers more ground, so your pedaling has a much greater effect. Car wheels work the same way.

Artwork: A wheel can work as either a force multiplier or a speed multiplier (but not both at the same time). If you turn the outside (rim) of a wheel, the axle at the center turns with less speed but more force, so the wheel works as a force multiplier. If you turn the axle instead (as a car does), the wheel becomes a speed multiplier. The axle turns only a short distance (blue arrow), but the leverage of the wheel means the outer rim turns much further (red arrow) in the same time. That's how a wheel helps you go faster.

Wheelbarrows combine wheels and levers to brilliant effect. A wheelbarrow makes it really easy to transport a load from one place to another—for two reasons. First, its long frame acts like a lever, so the load is much easier to lift. Second, it's easier to push the load using a wheelbarrow because the only friction is between the wheel and the axle. If you pushed the load across the rough surface of the ground without using a wheelbarrow, the friction would be much greater.

Gears

Photo: A gear is made from two or more wheels of different sizes with teeth cut into their edges to ensure they "mesh" (turn together without slipping).

Gears are wheels with teeth that can either increase the speed of a machine or its force, but not both at the same time. Bicycles use gears in both ways. If you want to pedal up a hill, you use gears to increase your force so you don't have to work quite so hard, although the catch is that they reduce your speed at the same time. If you're racing along a straight road, you can use gears to increase your speed, but this time the catch is that they'll reduce your force. Although it's not obvious just by looking at them, gears work in exactly the same way as levers (just as wheels do). That takes quite a bit of explaining so we won't go into more details here. Instead, you can read all about it in our gears article.

Pulleys

Put two or more wheels together and loop a rope around them several times and you create a powerful lifting machine called a pulley. Each time the rope wraps around the wheels, you create more lifting power or mechanical advantage. If there are four wheels and the rope wraps around them, the pulley works as though four ropes are supporting the load. So you can lift four times as much, although the catch is that you have to pull the rope four times further. Read more in our pulleys article.

Ramps and wedges

If you've ever helped pull a boat out of the sea, you'll know it's easier to do it if there's a ramp on the shore. Instead of lifting the boat vertically, straight up, you can get it out of the sea with much less force if you go up the ramp. You use less force, but you need to pull the boat a longer distance—so you use the same amount of energy in each case. Hillwalkers sometimes use the idea of a ramp to get to the top of a steep climb. By zig-zagging from side to side across their climb, they effectively create their own ramp. The hill becomes less steep, but they have to walk quite a bit further to get to the top.

Ramps are sometimes known as inclined planes or wedges. The head of an axe is a wedge working in a different way. An axe forces wood apart in two ways. The handle works like a lever, magnifying the force you apply. The wedge-shaped blade concentrates the force over a smaller area, increasing the pressure on the wood and splitting it apart. The blade of a knife works the same way.

Artwork: The head of an axe works like a ramp. When it powers into wood, the wood splits apart along the diagonal. That means you can cut the wood by applying a smaller force over a larger distance. If you wanted to pull a log apart with your bare hands, you'd need to apply a much bigger force (though over a much shorter distance).

Screws

Photo: The spiral thread on a screw means it takes longer to drive it into wood but—theoretically at least—you need less effort. The grooves also help the screw to remain in place.

A screw bites into wood when you turn it around. You often read science books that say a screw is "like a ramp wrapped around in a circle", which is pretty confusing and hard to understand. But imagine you're an ant and you want to climb from the bottom of a screw to the top. If you climb vertically up the outside, you go a relatively short distance but it takes an awful lot of climbing force. If you walk up the screw thread, winding around and around, you're really walking up a kind of spiral staircase—a ramp wrapped around in a circle. Yes, you walk much further, but it's a whole lot easier. There's another good thing about a screw too: because the head is bigger than the shaft beneath it, a screw works like a wheel (or lever): each time you turn the head, the sharpened point beneath bites into the wood with greater force. The tapering (cone-shaped) design makes it easier to drive in the screw.

Machines are all around us!

That's pretty much all there is to the science of simple machines. Once you understand how machines work, you start seeing them everywhere. Even your body is packed with machines. Your skeleton, for example, is a collection of levers! Take a look around your home and see how many more "simple machines" you can spot. You'll be amazed how many there are!

Photo: Lots of everyday tools contain several simple machines. I can count at least five on this corkscrew and bottle opener. The bottle opener on the right is a wedge. Once you've jammed it under a bottle-top, you use the rest of the (folded-up) corkscrew as a lever to jack the bottle open. The corkscrew contains another three simple machines. To open a wine bottle, you push the screw down into the cork. Then you use the levers to force the cork up and out of the bottle. The screw is linked to the levers by a kind of worm gear.

Is there a catch?

Lifting, cutting, chopping, moving, bending—machines like the ones we've explored up above make it easier to do all kinds of things by making forces bigger than you can normally create with your own body. At first sight, that sounds like it might open up the way to designing a machine that can give us something for nothing—maybe one that can make energy out of thin air, or a perpetual motion machine that runs forever.

In practice, the laws of physics are strict and if you make life easier for yourself in one way, you always make it harder in another to compensate. That's the scientist's way of saying "there's no such thing as a free lunch," and, in physics, it goes by the name of the law of conservation of energy (simply put: we can't make energy appear magically out of nowhere). So whenever you have a machine that gives you more force, it doesn't give you extra energy you didn't have before. With a pulley, for example, ropes and wheels give you much more lifting force, but you have to heave them much further, so you use exactly the same amount of energy as you would have done before. You just use it more slowly, with less effort, so the lifting feels easier. In the same way, you can use a see-saw to lift a much heavier friend by sitting further from the balancing point than they are, but you have to move your legs much further to compensate. You get extra force, but no extra energy—and that's the catch.

Artwork: A seesaw lets you create extra lifting force. The little red person can lift the big blue person by sitting further from the pivot point. That means they can lift a bigger force, but the catch is that they have to move their own body over a much bigger distance. This machine makes more force, but no more energy.

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On this website

• Axles and wheels
• Drilling
• Gears
• Hydraulics
• Pneumatics
• Pulleys

Books

These are broadly particularly suitable for ages 7–12:

Simple machines

• Making Machines with Levers by Chris Oxlade. Raintree, 2016. This is one of a series of six activity-driven books covering levers, wheels and axles, pulleys, ramps, screws, and springs. Ages 7–9.
• Simple Machines: Forces in Action by Buffy Silverman. Heinemann Library, 2016. A typical 48-page curriculum-based guide.
• The Kids' Book of Simple Machines: Cool Projects and Activities That Make Science Fun by Kelly Doudna. Mighty Media, 2015. An activity-driven guide covering each of the simple machines in turn.
• How Machines Work: The Interactive Guide to Simple Machines and Mechanisms by Nick Arnold and Allan Sanders. Templar, 2011. A short book and hands-on experiment kit that introduces 12 simple machines for ages 7–9.
• The Science of Forces: Projects and Experiments with Forces and Machines by Steve Parker. Heinemann, 2005. A 32-page hands-on introduction to things like gears and ramps.

Forces

• A Crash Course in Forces and Motion with Max Axiom Super Scientist by Emily Sohn. Capstone, 2019. A graphic-novel (comic) treatment that will appeal to more reluctant readers (though it does sometimes distract a little from the key takeway points).
• Can You Feel the Force by Richard Hammond. DK, 2007/2015. A sparky, humorous look at the physics of forces. (I was one of the consultants and contributors to this book.)
• Force and Motion by Peter Lafferty. DK, 2000. One of the series of excellent Eyewitness volumes from Dorling Kindersley covering the history, science, and technology of forces in our world.