Moving a boat you're standing on

Today's class will be a discussion of the definition and meaning of the informal word 'typo'.

Little Billy, why don't you start the discussion by giving the definition?

Show your working.

Your surname reminds me of a Japanese man with false teeth.

Search failed. What do you suggest I type into a search engine?

How about "sail".

A bar of soap hung over the transom, or perhaps a net bag full of camphor? (lowers surface tension at the stern and the boat gets 'pulled' along. Never tried it though)

No, the whole point of the question is can you move it by running up and down it.

In message snipped-for-privacy@4ax.com, Chris Hogg snipped-for-privacy@privacy.net writes

I seem to recall being shown this as a child. Paper boat on a tray of water with methylated spirit wicked over the stern with a wool thread:-)

A more fun thing to do is put some detergent into your pond and watch all the pondskaters drown.

Yep. I didn't know it worked with meths, but I guess anything that reduces the surface tension of water would do. Apparently it's called the Marangoni effect. Here's a Youtube clip showing it working with camphor

hogwash relative to other forces

"Can you move a boat while standing on it without touching the water?"

Everyone has ignored special "boundary cases":

- If the boat is moored alongside a dock then (after undoing the mooring lines) use an oar to push against a bollard on the dockside

- If the boat is in a "bay platform" dock, push the oar against the "buffer stop" end of the dock

- Out in the open water, is it cheating to use the boat's propeller to move the boat - you are not *yourself* touching the water?

It reminds me of a wonderful reply to a physics question, quoted in an after-dinner speech:

(speech by Magnus Magnusson, "Pass the Port", 1976, ISBN 0 9504923 1 0, pages 165-166)

My favourite after-dinner story originally came from the "Engineers Weekly" of Denmark. It illustrates the virtues - and pitfalls - of "thinking for oneself"; and I told it myself, not after dinner but before lunch, at my Installation as Rector of Edinburgh University in the McEwen Hall, Edinburgh, on February 21, 1976 - and got away with it!

It concerned a question in physics in a degree exam at the University of Copenhagen.

The question was: "Describe how to determine the height of a skyscraper with a barometer."

One student answered as follows:

"You tie a long piece of string to the neck of the barometer, then lower the barometer from the roof of the skyscraper to the ground. The length of the string, plus the length of the barometer, will equal the height of the skyscraper."

This highly original answer so incensed the examiner that he failed the student with contumely. The student appealed to the university authorities on the ground that his answer was indisputably correct, and that he should have been given full marks.

The university appointed an impartial arbiter to decide the case, a visiting professor from the University of Washington, called Dr. Alexander Calandra. Dr. Calandra ruled that although the answer was technically correct, it did not display any noticeable knowledge of physics; and to resolve the matter, he called the student in and gave him six minutes in which to answer the question verbally in a way that showed at least a minimal familiarity with the basic principles of physics.

For five minutes there was complete silence. The student sat there frowning heavily, deep in thought. Dr. Calandra reminded him that time was running out, to which the student replied that he had several extremely relevant answers to the question, but could not make up his mind which one of them was best.

"You had better hurry up," said Dr. Calandra.

"All right then," said the student. "You take the barometer up to the roof of the skyscraper, drop it over the edge, and measure the time it takes to reach the ground. The height of the building can then be worked out in terms of the formula H = ½gt^2 (height equals half times gravity-time squared). But bad luck on the barometer.

"Or if the sun happens to be shining, you could measure the height of the barometer, then set it up on end and measure the length of its shadow. Then you measure the shadow of the skyscraper, and thereafter it is a simple matter of proportional arithmetic to work out the height of the skyscraper.

"But if you, wanted to be highly scientific about it, you could tie a short piece of string to the neck of the barometer and swing it like a pendulum, first at ground level and then on the roof of the skyscraper, and work out the height of the building by the difference in the gravitational restoring force (T = 2 pi square root of l over g).

"Or if the skyscraper had an outside emergency staircase, it would be easier simply to walk up it and mark off the height of the skyscraper with a pencil, in barometer-lengths, and then add them up.

'' If you merely wanted to be boring and orthodox about it, of course, you could use the barometer to measure the air-pressure on the roof of the skyscraper, compare it with standard air-pressure on the ground, and convert the difference in millibars into feet to give you the height of the skyscraper.

''But since we are constantly being exhorted to exercise independence of mind and apply scientific methods, undoubtedly the best way would be to knock on the janitor's door and say to him, 'If you would like a nice new barometer, I will give you this one if you tell me the height of this skyscraper." [/quote]

I've often wondered if you were in deep space i.e no gravatational effects from other bodies and you were floating in a sealed sphere but you could use a valve , so you could fart in to space. would the sphere move due to equal and oppersite forces and if so what speed could be achieved and would you continue to accelerate. if in a true void could you reach lightspeed, or would you just eventually slow down and stop, if so how long would it take. But then again I've never been able to find out if there's an SI unit like a Richter scale for farts. As that would need to be known for any such calculations.

But he wasn't provided with any string. He was provided with a barometer, nothing more.

Throw some object from the boat as hard as you can off the stern. That will move the boat forward a bit.

Which applies nowhere is space since the gravitational field of all bodies reaches to infinity.

You're describing a rocket engine which will accelerate you forwards as longs as it runs. The velocity you reach depends on how much material you eject and at what speed.

If a 20mm isn't big enough for you, then use a GAU-8 30mm, which has a recoil force of 10,000 pounds-force.

For 6 points, explain in detail why this doesn't thwart the conservation of energy.

FFS, you remind me of someone I won't name who tried to convince me that a tennis ball continued to accelerate once it had left the racket strings.

Acceleration only occurs while the force is taking place, i.e. the fart continues. When you stop farting, you stay at that speed forever. You could then later fart again to increase your speed, but the speed of a fart isn't much compared to rocket thrusters, so you wouldn't make yourself and the mass of the sphere accelerate much before you ran out of methane.

So he can't use himself. He can't use his hand to open any doors.