Debunking the 800 RPM myth

If you’ve spent any time at all in the wonderful, supportive, but sometimes misguided corners of the “cloth nappy internet,” chances are you’ve stumbled upon a piece of advice that, frankly, needs a good spin cycle itself to get rid of – the idea that you should never set your spin cycle higher than 800 RPM.

Let’s get this out of the way right now: this is a myth. A persistent, well-meaning, but ultimately inaccurate myth. Normally, our laundry science focuses on chemistry, but today’s lesson is all about physics.

What happens inside the washing machine

During the wash component of the wash cycle, items bump and grind against each other and the drum in the laundry equivalent of a busy nightclub. This physical agitation removes dirt and grime. It is also where damage is most likely to happen. Common culprits are an overloaded machine and snags from items catching on open zippers and Velcro tabs. 

Meanwhile, the spin cycle involves rotating the drum of the washing machine at a set number of revolutions per minute (RPM). Instead of moving around the machine, items are forced against the sides of the drum.

At the end of the spin cycle, items are pressed evenly around the edge of the drum. Sometimes you need to peel them off the sides and top.

How spin cycles work (no magic, just physics!)

Whether you’ve got a trusty front loader or a robust top loader, washing machine spin cycles operate on centripetal and centrifugal force. 

Centrifugal and centripetal force in action

Ever held a bucket of water and swung it in a circle over your head? When the bucket is at the very top of its swing, completely upside down, the water doesn’t fall out. It feels like magic, but it’s actually physics.

• The water wants to go straight (inertia): The water in the bucket wants to keep moving in a straight line – that’s called inertia. Even though you’re swinging the bucket in a circle, the water keeps trying to fly off in whatever original direction it was going in.
• The bucket keeps it in (centripetal force): The bucket stops the water from flying away. Its sides and bottom are always pulling the water inward, toward your hand. This inward pull that keeps the water moving in a circle is called centripetal force.
• It feels like being pushed out (centrifugal force): If you were a tiny person inside the bucket, it would feel like you’re being pushed outward. That feeling is called centrifugal force. There isn’t actually a real force pushing you out, it’s just perceived that way because your body (or the water) wants to go straight, while the bucket keeps pulling you in.
• Why the water stays in at the top: At the very top of the swing, the bucket is upside down – but the water still stays in. That’s because it’s moving fast enough that the inward pull from the bucket is stronger than gravity pulling down. The water is pressed into the bucket by its own motion.

The water stays in because it’s moving fast in a circle. Its inertia wants it to go straight, but the bucket pulls it into a circular path, and that keeps it stuck inside, even upside down!

The washing machine spin cycle

A similar thing happens during your washing machine’s spin cycle.

The drum acts like the bucket, providing the centripetal force that pulls your wet nappies into a circular path.

However, unlike in the bucket example, washing machine drums are perforated, meaning they’re full of small holes. The water in the nappies, due to its inertia, flies straight outwards through those tiny holes. This “flinging” sensation is the centrifugal force pushing the water out of the drum, removing it from the nappies.

The faster your machine spins, the more water gets pulled out of your nappies — and the difference adds up fast. Even a small increase in spin speed can make a big difference in how dry they come out.

How much more effective is a higher spin speed?

More force = more water expelled = drier nappies and clothes. But by how much?

Comparing relative force

If you plotted these figures on a graph, they would create an exponential curve. So how does that work?

Calculating relative force

Dust off your high school textbooks, because it’s time to get technical.

F_c = mrω²

That’s the formula for centrifugal (and centripetal) force. It depends on three things:

• m = mass
• r = radius (how far from the centre)
• ω = angular velocity (how fast it’s spinning)

To see how spin speed affects force, we focus on ω². So we say: F_c ∝ ω²

That just means: centrifugal force increases with the square of the spin speed.

In physics, spin speed is usually expressed in radians per second (rad/s), but that’s not very useful for everyday stuff. Washing machines use RPM instead. Since both measure rotation, we can treat them the same here: ω² ∝ RPM²

Which means: F_c ∝ RPM²

Now the fun part – we can use this to compare spin speeds!

If we increase our spin speed from 800 RPM to 1200 RPM, that’s (1200 ÷ 800)² = (1.5)² = 2.25.

This means spinning at 1200 RPM creates 2.25 times more force than 800 RPM, or 125% more. That’s a lot more water squeezed out of your laundry!

In mathematical terms, centrifugal force and spin speed have a quadratic relationship. Simply put, any increase in RPM is a big gain in how much water is removed from your nappies during the spin cycle.

The benefits of a higher spin speed

All this maths translates to some big advantages in increasing the spin speed for your nappy washes.

• ⚡ Use less energy for drying: If you use a clothes dryer, you will save power as your nappies will take less time to dry.
• 🌞 Faster drying times: If you are air-drying, your drying time is significantly reduced. With a smaller stash, this might be the difference between continuing with cloth during winter and needing to reach for disposables!

The takeaway

This post got far more technical than we intended it to be. Our original idea was a light-hearted look at an enduring cloth nappy myth rather than a physics lesson.

The takeaway is don’t be afraid to use the higher spin speeds your washing machine offers for your cloth nappies! Getting as much water out as possible in the wash cycle results in dryer nappies, not damage.