A prototype from Japan for writing on water using waves.
The boys have got a toy plane that happens to be a stealth fighter, and I told J that it was hard to see with radar. He asked how this was, and I told him that special paint on the plane cancels out the radar waves, and I’d tell him more when we went to Hunstanton, by drawing on the beach. Due to the unpleasant weather and cramming lots of things in this didn’t happen.
He reminded me of this tonight and I told him that it would have to wait till tomorrow but there’s an interesting thing that uses the same physics (the Japanese writing bath thing) which impressed him appropriately and got him off to bed. So tomorrow, if he remembers, we’ll be talking about the superposition of waves. I don’t think I’ll use the word superposition, probably adding instead.
On the way up to bed he asked me in a slightly worried voice “If the President of America finds out that we’re talking about this will he get cross with us?” I asked him what he meant, and he was worried about the wave stuff (not stealth technology) and I said it was just the special paint on the stealth plane that was secret. The physics itself was alright, and his aunt, grandfather, grandmother etc. all knew it already. Phew! Not about to be carted off by Americans in dark glasses just yet, then.
Oh, that’s so cool!!!!!!
That is very cool and reminds me of The Abyss!
Well, you taught me something today as well. I didn’t know about the special paint on stealth planes, always wondered how they avoided radar!
Thanks 😉
If I’ve got it right, the anti-radar paint works in the same way as rainbows on soap bubbles. The radar wave hits the front surface of the paint and some bounces off (which normally would be detected in the normal way i.e. the plane shows up on radar). However, not all of it is reflected by the front surface and the rest carries on through to bounce off the back surface of the paint i.e. the paint / metal boundary. The clever bit is getting the paint just right, so that the two reflected bits match up in the right way so that they cancel each other out i.e. there’s no reflection to go back to be detected. (A trough in one wave coincides with a peak in the other wave and vice versa, so they are each other’s evil twin and cancel out.)
This happens in soap bubbles too, but with light. The white light of sun light is a mixture of all the colours in the rainbow, and the difference in colour corresponds to a difference in the wavelength of the light. The reflection from the front surface and the reflection from the back surface cancelling each other out trick only works for one of the colours i.e. the one with a wavelength that fits with how thick the soap bubble wall is at that point.
The wall of the soap bubble isn’t the same thickness all over, so the colour that gets knocked out of the mix varies as you move around the surface of the bubble, which gives rise to the rainbow. Ain’t physics great!