I used to believe that houses were built on ball-bearings about the size of a bowling ball. Much later I realised that this must have stemmed from my dad trying to explain that the world was round.

I used to believe…
My friend Baz believed that a large truck travelling along a road would stop dead for a tiny fraction of a second each time a fly hit the windscreen (that's a "windshield" for you folks from the US of A). He was aged 33 when he let that one slip!
I sed to think that thw only reason we stuck to the earth was because is spins around!
I used to believe…
Me and my sis who is two years younger then me used to try to make ways to fly like putting blankets on our tricycles handle bars. Once I got this great Idea that I would take a box and tape feathers to it and slide down the slide and go flying. At the last minute I got concerned about safety. I decieded I had better tie a rope to the top of the slide so I wouldn't crash land. believe it or not the rope held good the problem was it was only half the lenth of the slide so I "Crash Landed" without my box. I got some bruises from that one.
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I used to believe that if you shouted into a balloon whilst blowing it up and then tied it up, the same noise would come out later on when you popped it!
I used to believe that when tieing knots in rope that the more normal knots you "stacked" on top of each other the stronger the knot would be
I used to believe…
when i was about 6 we did a project at school about space and our teacher told us about 'black holes' that were big enough to suck in the earth and squash it. I was terrified and for several weeks i used to pray every night that the earth wouldn't get swallowed. Then i think i forgot about it!
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i used to believe if i dug a whole big enough i could find gravity, i found some polestirine so for years i was convinced gravity was white
i used to believe that if you were in a falling elevator, you could just jump at the last minute before it crashed at the bottom of the lift shaft, thus reversing your direction while the lift crashed around you. Then you'd land (still inside the mangled lift wreckage) as if you were landing after a normal jump. Genius.
I went for a short time as a child beleiving that I should be able to support myself on something I was holding up: take a metal pole, hold it behind your back horizontally, crouch slightly as if sitting on it then try to lift your feet off the ground. Even though I tried and failed, I was convinced I just wasn't doing it right.
I used to believe…
It doesn't fit the vehicle categories, but I think this one's pretty good:
When we were kids a friend of mine thought a ten centimeter long propeller driven ship I had in my bathtub was exactly as fast as the ferrys from Norway to Denmark, because it was a copy of one of them. I disagreed even though I was two years younger. We got into a really long and tiresome argument about it, and I don't think we ever managed to agree. It's been years since I saw him, but if I run into him maybe I should ask if he still thinks it could be the case. He's 34 now.
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I didn't think you could put out a fire with hot water - only cold water would do.
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I used to believe that the tiny flashes you sometimes see when you have your eyes closed were neutrinos passing through your eyes.
I used to believe…
During the "nukular" 80s I had a fair idea of the power of an 'atom bomb', but couldn't figure out why it was so darned big when I'd been told in school that an atom was a really really really small part of the universe.
I always got confused when I watched movies with pepole jumping of trains or cars that was moving. Thats because I thought that if I just stepped of I woudld immediatley stand still, not faling and hurt myself. Because it was the cars or train that was moving, I just sat there...
I used to believe…
As a seven-year old, I believed that every noise ever made or that will be made goes directly to a cave in some vast mountain, and that they will remain there until the destruction of the earth when they will all be released simultaneously.
I used to think that filling a plastic bag with air took away the gravity inside.
I spent many hours at my grandmothers testing this theory with a plastic sandwich bag and a ten cent coin.
I used to believe that if I dug up my garden enough I would discover a completely new colour that no-one else had ever seen before. I tried to imagine what this colour would be, and it was always orange.
I used to believe…
Somehow I got this strange idea that if you held a piece of paper so that it's edge was facing a piece of glass, and pushed it fast enough it would actually travel through the glass without the glass breaking. I thought it was a phonomenon associated with time travel but later as I discovered that all material thigs were made up of atoms I figured that the paper was actually squeezing through the spaces in between the molecules. Actually none of my experiments to make the paper pass through the glass ever worked but I figured that it was because I couldn't move the paper fast enough.
I used to believe…
As a child I used to spin myself around and around. When I'd stand still after spinning the room would be moving around and I was convinced that I was witnessing the earth rotating on its axis.