Topsy-turvy images with a glass of water

We bought a set of Mr Men books (by Roger Hargreaves) at the start of lockdown and have been giving them to the boys as prizes in treasure hunts every few days.  It's a good way to get our 3 year old to practice his reading (he can recognise the word 'under' instantly now!) and they've both been enjoying some new books in the absence of being able to go to the library.  My 3 year old has been particularly taken by Mr Topsy-Turvy, so I thought he might be amused by an activity which made topsy-turvy words back to normal and turned other things around the wrong way.

The bottom 'hello' is printed in reverse

You can use a cylindrical object filled with water (a glass or a bottle) to reverse an image.  I didn't try and explain why this happens to my son as it's conceptually pretty tricky - the water bends (refracts) the light, and due to the circular shape of the water which the light passes through, the light bends to a focal point somewhere between your eyes and the water.  Viewed from beyond this focal point, the image appears reversed - you can check this by moving yourself to different distances from the water glass.

No right turn?

I started off by showing him his name printed the correct way round, and reversed (I made the text into an image and then flipped it in OpenOffice, there are no doubt easier ways to do it).  We looked at the words and he read his name the right way round, then backwards (which he found surprisingly easy), and he told me it was topsy-turvy.  I put it behind the water glass so the right way around version was above the level of the water and the reversed one below, and positioned him so he could see them both reading his name correctly.  He thought this was pretty neat, but wanted to check it was still the wrong way behind the glass.  We then repeated this with the word 'hello' (a poor choice in hindsight as it's not simple to read using basic phonics).

It's actually a no left turn sign at the bottom

He's also into reading road signs, and I've made him a set of cardboard ones to insert into little holders in his Magformers magnetic squares (they came with four signs, but they weren't ones he particularly likes!), so I put a no left turn and no right turn in, and then showed him how they looked the same behind the water glass.

Mr Topsy Turvy is walking the other way!

Then I asked if there was anything else he wanted to make the right way round, or indeed make topsy-turvy, and he said Mr Topsy-Turvy.  So we had a look at the book cover with the water glass, and found that he faced the other way (but his hat is still upside down!).  He lost interest pretty quickly so I didn't show him the upside down image he could see by looking from lower down, but he seemed to be amused for a while.  When he's a bit older, I'll try and explain to him why the water glass has the effect he saw.