Mad About Physics: Examining Braintwister No. 90 - The Three Hole Can

[TVP45]

Does anyone own the Jargodzki and Potter book Mad About Physics? If so, could you examine braintwister no. 90, the three hole can? They seem to claim that, if you have a cylindrical can filled with water and there are three identical holes, one near the top, one near the middle, and one near the bottom, that the water will shoot the farthest horizontally from the middle one.

What is the "trick" here? Have I missed a clever wording?

 

[Doc Al]

No trick. Did you read the solution in the back of the book? The calculation is straightforward.

 

[TVP45]

I'm sorry. Poorly worded question. Why would someone be puzzled by this? It seems consistent with ordinary experience (except for the problem of crossing streams - that seems like more of a braintwister).

 

[Doc Al]

I guess if you've never had the experience, it might not be obvious that the illustration is incorrect and that it's the middle stream that goes the farthest. When I first came across this problem (a gazillion years ago) I had to do the calculation to fully understand it.

Maybe you're just too smart!

 

[TVP45]

I suspect I'm too literal. I often don't get satire (On the good side, that makes it hard to insult me) or jokes.

Thanks. I just needed a second set of eyes to point out the puzzle.

 

[A.T.]

Does anyone own the Jargodzki and Potter book Mad About Physics? If so, could you examine braintwister no. 90, the three hole can? They seem to claim that, if you have a cylindrical can filled with water and there are three identical holes, one near the top, one near the middle, and one near the bottom, that the water will shoot the farthest horizontally from the middle one.

What is the "trick" here? Have I missed a clever wording?

I don't have the book. Is this an optimization problem of initial horizontal velocity vs. initial height? Is the can placed on the ground? If you hold it up it, could it change the result?

 

[TVP45]

I don't have the book. Is this an optimization problem of initial horizontal velocity vs. initial height? Is the can placed on the ground? If you hold it up it, could it change the result?

Sure. That would make an interesting variation, that is, putting legs on the can.

 

[Danger]

I suspect I'm too literal. I often don't get satire (On the good side, that makes it hard to insult me) or jokes.

Well then, I guess that I won't be conversing with you much.

 

[RonL]

I suspect I'm too literal. I often don't get satire (On the good side, that makes it hard to insult me) or jokes.

Some may have noticed that about me as well.

 

[TVP45]

Well then, I guess that I won't be conversing with you much.

Actually, your post jogged my memory and I realized why I knew which hole would spurt the farthest. When I was a kid, we used to shoot holes in 55 gallon rain barrels. Thank god the steam trains went away just about the time I got my first gun or I'd probably have tried the water tanks for those.

Glad to see you're staying one step ahead of the Mounties.

 

[Danger]

Too cool.
Despite your denial, you obviously have a great sense of humour.

 

[Born2bwire]

Actually, your post jogged my memory and I realized why I knew which hole would spurt the farthest. When I was a kid, we used to shoot holes in 55 gallon rain barrels. Thank god the steam trains went away just about the time I got my first gun or I'd probably have tried the water tanks for those.

Glad to see you're staying one step ahead of the Mounties.

There is no better way to demonstrate the joys and laws of physics to youth than the after effects of high pressure gas expansions via exothermic chemical reactions.

 

[Danger]

There is no better way to demonstrate the joys and laws of physics to youth than the after effects of high pressure gas expansions via exothermic chemical reactions.

Hence my diet of beans and beer.

 

[TVP45]

Too cool.
Despite your denial, you obviously have a great sense of humour.

So, do you wonder why just the sight of a post from you reminded me of doing something I absolutely should not have been doing?

 

[Danger]

So, do you wonder why just the sight of a post from you reminded me of doing something I absolutely should not have been doing?

Naw... I'm getting used to it.

 

[TVP45]

There is no better way to demonstrate the joys and laws of physics to youth than the after effects of high pressure gas expansions via exothermic chemical reactions.

I took physics back in the dark ages before safety regs and political correctness. My General Physics professor had several demos in which he used a rifle. Gone are those days...

 

[GrizzlyBat]

I remember getting a physics question in an assignment that was kind of like this, but we had to use calculus to find the maximum range. You end up finding that the velocity is as if the water had fallen that distance due to gravity, then you also find that the middle is the best hight because of range being the maximum.