Do You Know?

[GreatLakesGramma]

If you have a piece of sheet metal with a hole in the middle, and you heat it, will the hole get larger or smaller?

[Outta Here]

Try this: http://www.science.edu.sg/ssc/detailed.jsp?artid=2660&type=6&root=5&parent=5&cat=54

[GreatLakesGramma]

I already know the answer, I just wanted to see what everyone thinks. My son got the question in his email from the Ripley's Believe It or Not site. The answer came the next day. My guess was wrong. My husband got it right.

[carolaa]

Let's see. Most things expand in the cold, so the metal should contract in the heat, making the hole bigger. That's my guess.

[olger]

Metal expands when exposed to heat..

[Gerr]

Which means the hole should get smaller.

[carolaa]

Metal expands when exposed to heat..

Well, I was thinking that, but then I thought most things expand in the cold, so that must be wrong. But I will trust you on this one.

[LifeHiscost]

Originally Posted By: olger

Metal expands when exposed to heat..

Well, I was thinking that, but then I thought most things expand in the cold, so that must be wrong. But I will trust you on this one.

When you have a metal lid on a glass jar, difficult to turn off by hand, put it under a stream of hot water and soon it will turn off easily. Which also seems to prove that glass does not expand as much or as readily as metal. Yes?

[olger]

Take a steel ball bearing and a ring that the bearing fits through with .003 clearance. Apply torch to the ball and push it through the ring. Won't go..

About the only things that expand with cold are freezable liquids, or things that have water in them ie earth..,

[Bravus]

And of freezable liquids, water is almost unique in expanding when it freezes. Most others contract. If water did that, life would be impossible on this planet (at least, life as we know it).

I find this question tough, though. The metal expands, and we know what happens with a ring. But a sheet might be different, and the material might expand in a way that both makes the outside area of the sheet bigger and makes the hole smaller...

[Planey]

Imagine the sheet of metal without the hole drilled in it yet. Mark the circle where the hole is to be drilled.

When you heat the sheet up, presumably evenly, the expansion would also take place evenly. Now look at the circle you marked. As the whole sheet had expanded this circle must be bigger.

The expansion would I believe be the same if you removed the circle and made a round hole before you started heating.

Hence the hole should get bigger.

Graeme

[GreatLakesGramma]

Metal expands when exposed to heat..

[Bravus]

Planey is no doubt right, and his reasoning 95% convinces me...

But if the sheet were intact there'd be metal in the circle expanding. If there's air in the circle instead, there's nothing forcing the edges outward, and since the metal in the sheet is trying to expand in all directions, it's possible that it will expand into the available space - as it's doing around the outside edges of the sheet.

I'd need to see a range of empirical tests before I'd be 100% convinced.

[Dottie]

Wow! An amazing thing just happened! I agree with Bravus!! I thought the same thing, but could not explain it as I am poor with scientific stuff.

[GreatLakesGramma]

Well, according to the link Aubrey supplied, since the average distance between atoms increases when the metal is heated, the spaces in between metal atoms at the edge of the hole have to be bigger, so the circumference of the hole would have to increase. There is no scientific evidence included to prove it though. And I have been unable to find it at Ripley's site, so I don't know if they had evidence, or it was only theoretical.

[Amelia]

I will have to remember to bring this up the next time I talk to my poppy. He is a retired metalurgist from a steel mill.

[GreatLakesGramma]

Well, my husband is a certified auto body mechanic, though that is not how he makes his living anymore, since it doesn't pay very well. He works with sheet metal sometimes, doing body work as a hobby or for friends, so I figured he probably would know. And he did agree with Ripley's. And as an electrician, he works with metals all the time, though not sheet metals.

But for sure Amelia, your poppy will be able to settle the question. Please don't forget to ask him. We are all anxious to know now.

[Gerr]

Planey is no doubt right, and his reasoning 95% convinces me...

But if the sheet were intact there'd be metal in the circle expanding. If there's air in the circle instead, there's nothing forcing the edges outward, and since the metal in the sheet is trying to expand in all directions, it's possible that it will expand into the available space - as it's doing around the outside edges of the sheet.

I'd need to see a range of empirical tests before I'd be 100% convinced.

The expansion occurs in all directions. And the hole itself provides an edge, so that the metal should not only expand at the periphery but also inwards making the hole smaller. I won't be convinced until proven by experimental evidence. The medieval experts took Aristotle's opinion as to how many legs spiders had until someone proved him wrong by actually counting them!

[Planey]

Originally Posted By: Bravus

Planey is no doubt right, and his reasoning 95% convinces me...

But if the sheet were intact there'd be metal in the circle expanding. If there's air in the circle instead, there's nothing forcing the edges outward, and since the metal in the sheet is trying to expand in all directions, it's possible that it will expand into the available space - as it's doing around the outside edges of the sheet.

I'd need to see a range of empirical tests before I'd be 100% convinced.

The expansion occurs in all directions. And the hole itself provides an edge, so that the metal should not only expand at the periphery but also inwards making the hole smaller. I won't be convinced until proven by experimental evidence. The medieval experts took Aristotle's opinion as to how many legs spiders had until someone proved him wrong by actually counting them!

Does your wedding ring (supposing you are an infidel) get tighter or looser when it is heated?

Same principle.

Graeme

[Woody]

I dunno. I don't make it a practice of heating up my wedding ring.

[Planey]

I dunno. I don't make it a practice of heating up my wedding ring.

So you never wash the dishes then?

[Woody]

I have a modern convenience called a 'dishwasher'.

[Planey]

I have a modern convenience called a 'dishwasher'.

That's not a very romantic name for Blanche...

Graeme

[olger]

Planey is no doubt right, and his reasoning 95% convinces me...

But if the sheet were intact there'd be metal in the circle expanding. If there's air in the circle instead, there's nothing forcing the edges outward, and since the metal in the sheet is trying to expand in all directions, it's possible that it will expand into the available space - as it's doing around the outside edges of the sheet.

I'd need to see a range of empirical tests before I'd be 100% convinced.

I'll run a test here in the shop, and take readings with a micrometer. Report back....

[Gerr]

I don't have one. If I had one, I wouldn't heat it while it's on my finger to prove you wrong! Besides, if I heat up the ring, no doubt my finger would get hot too and expand, thus making it tighter and may give me the false impression you're wrong! Smile Graeme.