Can You Quantify the Upward Force of a Rising Boat on an Incoming Tide?

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Discussion Overview

The discussion revolves around quantifying the upward force exerted by a boat as it rises on an incoming tide, specifically focusing on a boat measuring 24 feet by 8 feet and weighing 4000 lbs. Participants explore concepts related to buoyancy, force, and the implications of holding the boat down as the tide rises.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how to quantify the upward force of a boat rising on an incoming tide and whether "force" or "work" is the appropriate term to use.
  • Another participant references Archimedes' Principle, suggesting that the force exerted by a floating object equals the weight of the water displaced, indicating that the extra volume of displaced water needs to be calculated to determine the force.
  • A participant notes that if the water level reaches the gunnels of the boat, a small downward force could potentially sink it.
  • Another participant proposes a hypothetical scenario of pulling a boat down and provides an example with a smaller boat to illustrate the concept of displaced water weight.
  • A later reply estimates that for the specified 24x8 boat, the upward force could be around 12,000 lbs, indicating a significant amount of force involved.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the concepts of force and buoyancy, with no consensus reached on the exact quantification of the upward force or the implications of holding the boat down.

Contextual Notes

Participants have not fully resolved the assumptions regarding the calculations of displaced water volume and the conditions under which the boat would be held down. There are also differing interpretations of the terms "force" and "work" in this context.

ckrizan
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Can anyone tell me how much upward force a boat (say 24 feet x 8 feet, weighing 4000 lbs) exerts as it rises 1 foot on an incoming tide? My son asked me whether or not someone could hold the boat down as it tried to rise and I thought not but can't quite figure out how to quantify how hard it would be to try. Is it something that would strain a rope if you tried to hold it down (assuming no stretch)? Is "force" even the right term? Should I be asking how much work is done?

Thanks.
 
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ckrizan said:
Can anyone tell me how much upward force a boat (say 24 feet x 8 feet, weighing 4000 lbs) exerts as it rises 1 foot on an incoming tide? My son asked me whether or not someone could hold the boat down as it tried to rise and I thought not but can't quite figure out how to quantify how hard it would be to try. Is it something that would strain a rope if you tried to hold it down (assuming no stretch)? Is "force" even the right term? Should I be asking how much work is done?

Thanks.

Welcome to the PF. You can read more about bouyancy under the topic of Archimedes Principle:

http://en.wikipedia.org/wiki/Archimedes_principle

The force exerted on a floating object is equal to the weight of the water displaced. So to answer your son's question, you will need to figure out the extra volume of water that gets displaced as you hold the boat in place and the water rises, and then figure out how much that extra volume of displaced water weighs.
 
If the water were up to the gunnels, a little downward force would sink it.
 
Similarily you could ask him how much force it would take to "pull" a boat down 1 foot.

hint: Let's say you have a 12'x4' boat. Then you have 48 cubic feet of displaced water. That's just under 3000 lb of displaced water...
 
Thanks everyone. So for I guess for my 24x8 example (assuming it's squared-off), that would be about 12,000 lbs of force. That's a lot.

Thanks again.
 

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