Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Canal Barge on Aqueduct
Name: Don
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A


Question:
Will a canal coal barge crossing an aqueduct put an additional load on the aqueduct?



Replies:
No. The condition that the barge floats means that it weighs precisely the same as the water that it is displacing. So, as long as the water level in the aqueduct is the same with and without the barge there, the total weight is the same too.


Ha! It seems I have the setup wrong. I thought an aqueduct was like a lock but in reading a little more, I guess it is a free-flowing channel. Thanks, Internet!

OK, but even in this setup, I still think change is non-zero.

Water cannot flow instantaneously out of the channel. So the load would not increase by the exact weight of the barge necessarily, but it will increase by the amount of extra water the barge drags with it. It depends on the barge (are these huge Mississippi River barges, or little floating-barrel type things?).

So that begs the question if we could create a scenario where would the supports see minimal change? I suppose we would have to have a very large (wide, deep, and long) channel (in which we can neglect wall effects and velocity gradients) and the barge is moving at the same speed as the flowing water (in other words its velocity is zero relative to the water). In this situation, the water is quiescent relative to the boat at all points of contact, and it simply displaces (moving) water.

I think the "weight does not change" answer sounds like once of these cute yet misleading "physics mind benders" that in reality selectively oversimplifies (it neglects momentum and viscosity).

Wow!

OK, well, I think the load will change, but I would only be speculating on how much. If we answer the literal question "does it change *at all*, I think the answer must be yes for the reasons I described. However, if we loosen the question to "does it change materially, compared with load tolerances" then I would say the answer is probably no (I mean, these things are not collapsing all the time, so they must have broad tolerances the way bridges do). I do not see any large wake or turbulence around the boat. So I think the change would be small and not significant relative to the structure.

Burr Zimmerman


Look at the attached picture and consider the weight of the people and the weight of the barge. How is the load displaced? Why do things float? How does a large warship float?

Leslie Kanat, Ph.D.
Professor of Geology
Department of Environmental Sciences



Consider the weight of the people and the weight of the barge. How is the load displaced? Why do things float? How does a large warship float?

Leslie Kanat, Ph.D.
Professor of Geology
Department of Environmental Sciences

http://www.youtube.com/watch?v=3Q6eetzzjMo



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory