How a spring works

You click the top of a ballpoint pen and it springs back on its own. You lie down on your mattress at night, it sinks a little, then gently pushes you back up. You squeeze a clothespin and it snaps open again. In every one of these moments, a spring is quietly working for you, almost always without you noticing.

In this guide we will explain, in very plain words and with no complicated terms, what a spring is and how it works. You do not need to know anything about engineering. If you have ever stretched a rubber band for fun, you already understand half the story.

What a spring is, in plain words

A spring is a piece of very bendy steel wire, coiled or bent into a special shape. That shape is the secret: it lets the spring store energy when you push, pull or twist it, and give that energy back when you let go.

Think of a spring as a tiny piggy-bank for energy that you can use over and over. When you press the pen, you put a little of your force into that piggy-bank. When you let go, it gives the force back and the pen pops out again. A spring does not create energy out of nowhere. It just holds the energy you gave it and returns it at the right moment.

That is why springs show up in so many things: whenever something needs to push back, pull back, or return to its place on its own, a spring solves the problem cheaply and reliably.

The three types you use every day

There are many kinds of springs out there, but for everyday life you only need to know three families. The difference between them is simply the kind of movement each one answers to: squeezing, stretching or twisting.

• Compression spring: this is the one that pushes back when you squeeze it. It usually looks like a chubby coil with space between the loops. Examples: the spring inside a ballpoint pen, the springs in a mattress, and a car's suspension, which softens the bumps in the road.
• Extension (tension) spring: this is the one that pulls back when you stretch it. Its loops sit tightly together when it is at rest, and it has hooks at each end. Examples: the spring that pulls a screen door shut, the springs on a trampoline, and the inside of a handheld luggage scale.
• Torsion spring: this is the one that reacts when you twist it, not when you squeeze or stretch it. It pushes back with a turning motion. Examples: a clothespin, the garage-door spring that helps lift the door, and a mouse-trap.

Why a spring is made of steel

The key word here is elastic. An elastic material is one that changes shape when you apply force and then returns to its original shape when you let go. The steel used in springs is very good at this.

Compare it with an ordinary paperclip. If you bend the paperclip once, it stays bent and does not come back. It simply is not elastic enough. Spring steel, on the other hand, can bend and return, bend and return, thousands upon thousands of times, without staying bent. It is like a hair tie that can take far more use.

That is why most springs are made of steel rather than plastic or aluminium. The right steel can store a good amount of energy in a small space and give almost all of it back, again and again, for years.

Soft spring or stiff spring?

Not every spring is equally stubborn. Some are soft and easy to squeeze, like the one in a pen, which you move with a single finger. Others are stiff and hard to move, like a car's suspension spring, which holds up the weight of the whole vehicle.

Engineers give this stubbornness a name: the spring rate, also called the spring's stiffness. It is just a way to measure how much force you need to move the spring a tiny bit, say, one millimetre.

A soft spring moves a lot with only a little force. A stiff spring barely budges, even under plenty of force. Neither is better than the other. Each job calls for the right stiffness: a pen needs a very light spring, while a car needs a firm one so it does not sink to the ground. Choosing this stiffness is one of the most important parts of designing a spring.

What can go wrong with a spring

Springs are tough, but they have limits, like almost everything. If you overdo it, two things can happen.

The first is the spring losing its shape. If you squeeze or stretch it too far, beyond what it was made to handle, it can stay deformed and never return to its original size. It is like stretching a hair tie until it goes loose and never grips properly again.

The second is the spring breaking after heavy use. Even when working within its limit, every movement causes a tiny bit of wear. After millions of back-and-forth cycles, a poorly sized spring can simply snap, in the same way a wire breaks if you bend it back and forth many times in a row.

The good news is that both problems can be avoided. A well-designed spring always works within a safe margin, far from the point where it would lose its shape or wear out too soon. That is why it pays to get the dimensions right before you have it made.

Where springs are hiding

Once you understand how a spring works, it is hard to stop spotting them. They are scattered all over your home and the street, almost always out of sight, doing quiet work.

• On your desk: pens, staplers, the mouse and keyboard, power sockets and switches.
• Around the house: mattresses, reclining sofas, trampolines and toys.
• In cars and motorbikes: suspension, brakes, the clutch, locks and the pedal that springs back on its own.
• In everyday objects: clothespins, garage doors, padlocks, wristwatches and the valve on a pressure cooker.

How molas.app.br makes it easy

You do not need an engineering degree to get a good spring. On molas.app.br you build your spring on screen by adjusting a few simple values, watch the design spin in 3D right away, and get the price instantly, with the calculations and safety limits already handled behind the scenes for you.