Who knows

[noseall]

A bit of fun brain teaser.

I've asked it before on here but I don't think I got a definitive answer. The same question was put to my customers (both educated) and even those could not agree. They both argued about water displacement and physics.

Canal - aqueduct - barge passes over the aqueduct. Do the aqueduct supports feel the weight of the barge? I'm in the yes they do, camp.

 

[Highway Man]

A bit of fun brain teaser.

I've asked it before on here but I don't think I got a definitive answer. The same question was put to my customers (both educated) and even those could not agree. They both argued about water displacement and physics.

Canal - aqueduct - barge passes over the aqueduct. Do the aqueduct supports feel the weight of the barge? I'm in the yes they do, camp.

No it doesn't. why do you think you can pull the boat with a rope and move it around without an engine. The same as a ship in the sea or anything else that floats is essentially weightless.

 

[noseall]

No it doesn't.

And yet the physics graduate disagrees. She said the aqueduct stanchions do feel the weight.

?

 

[Highway Man]

The bridge would feel the weight of the water but because the boat displaces the amount of water that it weighs the boat simply replaces the weight of the water.

 

[noseall]

The bridge would feel the weight of the water but because the boat displaces the amount of water that it weighs the boat simply replaces the weight of the water.

But is there ANY increase in pressure on the supports, as the boat passes over?

 

[MNW67]

But is there ANY increase in pressure on the supports, as the boat passes over?

No. Because nothing changes when the boat passes over. The aqueduct is open at both ends and is part of a much larger body of water i.e the canal system. If the boat wasn't situated above a particular support, then a weight of water exactly equal to the boats weight would be there instead. When the barge was first dropped into the canal system, maybe many years ago, there would have been an increase in weight spread across the whole canal system. But presumably the same weight of water would have drained out of the canal system somewhere to stop the water level from rising.

 

[Highway Man]

But is there ANY increase in pressure on the supports, as the boat passes over?

No and this can be seen in a submarine for an example. Take the sea bed as very fine sawdust. if you wave your hand over just above the sea bed the turbulence would cause the sea bed to make the water murky by turbulence. Place a 40 tonne submarine over the sea bed and turn off all of it's engines so it is just floating through its ballast, there would be no imprint on the sea bed or disturbance

 

[Highway Man]

I have studied this on a course I did once in the army. I studied 3 laws of Physics, Charles Law, Boyles Law and Archimedes principle.

 

[Highway Man]

No. Because nothing changes when the boat passes over. If the boat wasn't situated above a particular support, then exactly the same weight of water would be. When the barge was first dropped into the canal system, maybe many years ago, there would have been an increase in weight spread across the whole canal system.

Not quite right. There would be no downward pressure caused by launching a boat, the increased pressure would have been on the sides of the canal and not uderneath it.

 

[Highway Man]

Another fine example would be this. If you swim under a stationary boat, would you feel the weight of the boat above you? No you wouldn't, that is because the boat has displaced the water and has no affect below it. It took me a while to get my head around the principle but I had every example thrown at me which not only convinced me but proved by experiment the principle.

 

[MNW67]

I studied 3 laws of Physics, Charles Law, Boyles Law and Archimedes principle.

Eureka!

 

[Highway Man]

Eureka!

Archimedes principle when he sat in a bath.

 

[MNW67]

Archimedes principle when he sat in a bath.

I thought it was when he farted in the bath.

 

[Highway Man]

I thought it was when he farted in the bath.

No it was when the water went all over the floor, it's like @pete01 who is grossly overweight and can only put a small amount of water in the bath or risks flooding his bathroom.

 

[Notch7]

It depends on where the water displaced by the barge goes.

If you put a bucket of water half full on some scales, then added a model boat weighing 1kg the scales would go up by that amount.

If the bucket was totally full of water and when you put the boat in the displaced water went over the top of the bucket, then the scales wouldn’t change.