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 of a thumbtack (drawing pin) being pushed into a wall.
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: