Celestia Forums

I got to tell you what happened tonight when I went to my Audi garage to have the wheel nuts tightened after last week's mounting of my summer tires (yes in Hamburg the summer starts late ) .

It was a beautiful evening and my 1 year old Audi looked really cool in the warm evening sun... Then the car mechanic came and first pulled off with a special hook the round plastic-aluminium covers in the center of the wheels on one side of the car. Then he checked the tightening of the nuts. Everything went as usual. Next he went around to the other side of the car and tried to pull off the third cover. NOTHING. Rock-solid. Nothing moved. He went to get a special tool and tried again. Nothing. He pulled with all the force he had, his face turned red ...Nothing.

He was really very embarassed. In order to do at least something he went to try the 4th wheel: NOTHING AGAIN. Rock solid. ...And then I knew!

With a smile I suggested to him to poor some water over the two remaining covers. He looked at me in total despair , but in absence of a better alternative he went to fetch some water and did what I said. Obviously he thought I was nuts. After finishing with this he tried it again,...and of course they came off easily.

Sometimes, it's even useful to be a physicist

Cheers,
Fridger

... I don't get it.

Johaen wrote:... I don't get it.

That's what the mechanic also told me

t00fri wrote:

Johaen wrote:... I don't get it.

That's what the mechanic also told me

Teach them why Fridger...for they know not the practical use of the things they learn in school. They think we fill their minds with useless information. I can hear it now, "when will we ever need this in real life..."

Oh, hey, I got an idea. Maybe pouring water of the hubcap (ugh, hubcaps?) cooled it enough to make it contract and loosen it enough to pull it off.

Johaen wrote:Oh, hey, I got an idea. Maybe pouring water of the hubcap (ugh, hubcaps?) cooled it enough to make it contract and loosen it enough to pull it off.

Perfect Johaen!

Here are a few more details. The first observation that made me suspicious about heat being behind all this was that the mechanic did not have the slightest problems pulling off the two covers on the /shadow/ side of the car. My car however was only standing in the warm evening sunlight for about 5-10 minutes before the mechanic came. I noticed however that particular kind of plastic that I knew already from working with it on my lathe. It has an extremely high heat expansion coefficient! After the mechanic also did not succeed with the second cover on the sunny side, I was almost sure. The cold water did it's job already after ~1 minute. That's what made the whole effect so stunning.

What even surprised me was how tight this plug was really fixed to the wheel due to it's expansion. It's hard to describe in words. The mechanic had surely pulled off hundreds of such plugs in his life and ALWAYS they came off easily --as he insisted all the time--. He pulled so hard on one of the two "hot" ones that he offered to replace one of them, since the hole for the hook was already widened and didn't look all that well anymore . I even accepted...


After I stopped posting on the P&A board, I find Purgatory also has it's special charm for discussing some physics on and off


Cheers,
Fridger

so, did you laugh at him?

Hunter Parasite wrote:so, did you laugh at him?

Of course not. I explained the physics to him and he promised that he will remember this stunning effect for the rest of his life

Bye Fridger

I find it funny that they'd make the hubcaps out of that sort of plastic in the first place, unless the whole aim was to make sure they didn't fly off the wheel because they were wedged in so tightly!

But it's a good story anyway

[...] I went to my Audi garage to have the wheel nuts tightened [...]

Well, Fridger, let me drop this conclusion:

Physicist have two left hands!

They know what to do - but they can't do it themselves ...
... or they don't want to get their hands dirty.

Always remember an old mechanics wisdom: Nach fest kommt lose! (After tight comes loose)

Adirondack

Adirondack wrote:Physicists have two left hands!

That would be excellent in my case, since I am lefthanded

They know what to do - but they can't do it themselves ...
... or they don't want to get their hands dirty.

The latter is correct.

Actually, I don't have much of a choice. I conveniently have my winter/summer wheels stored and changed by this garage and the tightening is part of the package. It is free of charge. Indeed, I never do any work with cars myself (insurance). That's unrelated to whether I was able to do it or not.

But I have a VERY well equipped workshop in my basement! Besides the usual, it hosts a Swiss precision lathe, a band saw for metal, a heavy mounted drill, 2 storage oscilloscopes, a HeNe laser setup (for measuring the shape of the Schmidt plate of my Celestron telescope by interferometry...), as well as plenty of other electronic precision measuring equipment.

So it's not all that bad with my two "right" hands

Bye Fridger