I've always been fascinated by how a tiny spider can create a web spanning a gap where climbing and dragging a thread across the floor would be impossible, maybe between trees, from a building to a lamppost, or over a stream. How do they do that? Here's a common technique by many orb weaver spiders — known for building orb-shaped, or circular wheel-shaped webs — for bridging the gap and creating the web.

The spider stands on the edge and lets out a long thread. It waits for the breeze to blow the thread away from them. If the thread catches onto something it can form a bridge thread.

Once it catches, the spider may reinforce the thread and then put down other anchors. These then form the frame of the web into which it will add radial threads from the centre.

The spider may then put down an auxiliary thread that provides a non-sticky frame, together with the radial threads, for it to walk on while it lays down the final sticky capture spiral. It's then set to lie in wait.

Some spiders will eat their webs at the end of the night but leave a bridge thread in place — perhaps for you to walk into in the morning — ready to rebuild the next night.

There is a vast diversity of spiders and webs. This is a fairly common example, but even within orb spider webs, there are a ton of different strategies for capturing prey. But perhaps, the next time you spot a bridge thread spanning a seemingly impossible gap this will give you a thought as to how it might have been done.

Here's a common orb spider web as a static sketch

You can watch darwin's bark spider on the BBC creating a web spanning a remarkable 25 metres

A common orb spider web

Möbius strip: the mindbending shape with only one side.

It's very simple to create: take a long piece of paper, give one end a 180-degree twist and then stick the ends together. The simple shape just created has only one side. What??

You can test this by running your finger over the surface and you'll cover the entire shape and end up back where you started.

Try to follow the red ball in the animation as it follows the surface over the entire loop.

Möbius strips have a couple of other interesting properties including how cutting them in half down the middle simply makes a longer loop, and cutting a third of the way in over the full length will reveal two distinct yet interconnected loops. Fun to try!

SP 759 - Möbius strip - single.png

In case it's handy here's a static Möbius strip sketch

Möbius strip

A clever means of categorizing the size of rivers. It does this by looking at joins of tributaries. Each time two tributaries of the same order join together then the river goes up in order. So the start of a stream from a spring is the outermost branch — first order. When two first orders join together, the river is classified as second order and so on.

The largest river by Strahler stream order classification is the Amazon at twelfth order. This means that at least two order 11 rivers had to merge together before the river emptied into the sea.

Strahler stream order: Streams, rivers, the Amazon and how to organise them.

An amazingly simple, and ridiculously useful and successful mechanism that converts linear motion to rotational motion. It’s basically what allows us to take a force produced by, say, steam, or an explosion, and make a wheel turn. Stick a few of these together and time the rotation of each correctly, carefully controlling the explosions and the exhaust and you have an internal combustion engine that powers our cars. There’s a lot amazing to me about it, but I am still impressed with how effectively it takes something moving back and forth, and makes something spin round, and vice versa.

Sketchplanations tagged with animation