River over a River Bridge

[glassdave]

The mass of any boat in the above river/bridge will be exerted on the surface integral of whatever contains it. In other words the mas of the displaced water is basically distributed through a slight rise in depth and increased in psi on the containing surface. Through larger distances friction in the water can overcome this but the weight is still distributed evenly.

[Wobble]

I guess I was thinking more of the river lift pic. Correct....on the bridge the water would be displaced out into the canal and off the bridge, but the "lift" in post 7 would weigh more with a boat in it.

The lift always picks up the same level of water, any excess spills. So unless a boat is so big that it is sitting on the bottom of the lift it will always be picking up the same weight.

[Expensive Date]

The lift always picks up the same level of water, any excess spills. So unless a boat is so big that it is sitting on the bottom of the lift it will always be picking up the same weight.

Uhhhhh No I proved it last night take a plastic container fill with water then put on a scale.Take a small cup with about 5 or 6 quarters put in container make sure it floats and does not touch bottom.Scale will register the weight of the quarters even though they are floating in the cup.

[HaxbySpeed]

Wobble is right it always picks up the same amount of weight because the water displaced by the vessel is spilled overboard. According to Archimedes the water it spills over is equal to the weight of the boat.. If you fill your plastic cup to the very top and then dump in your quarters the water will overflow and what's left with the quarters will weigh exactly the same as it did without them..

[Expensive Date]

Respectfully disagree that would only be correct if one square foot of water weighs the same as one square foot of boat.or any other equal size of both.

[dockrocker]

Respectfully disagree that would only be correct if one square foot of water weighs the same as one square foot of boat.or any other equal size of both.

Nerd fight!!!!

[Expensive Date]

I spent two days discussing this with my 4.3 grade average son.I finally had to prove it last night.....only I proved he was right.

[DAREDEVIL]

No.

Ask yourself this.. A semitruck trailer full of birds sitting on the bed of the truck. Truck hits a bump and all birds go into flight within the truck. Does the truck all of a sudden weigh less?

LOL,,are u crazy ???? ofcoarse it will weigh less in that moment...or do u think birds don't weigh anything ???? HAHA

[Buoy]

Uhhhhh No I proved it last night take a plastic container fill with water then put on a scale.Take a small cup with about 5 or 6 quarters put in container make sure it floats and does not touch bottom.Scale will register the weight of the quarters even though they are floating in the cup.

Wait a minute.
If there is more room in the bucket before it overflows, then yes, adding the coins in the cup will increase weight. You have added to mass and volume.
The cup (with coins) will displace it's own weight in the water - no more, no less.
If the bucket is full of water, and you introduce anything else to it, it will displace it's own weight if floating in it. This would be by volume.
If you simply placed the item (not floating) in the bottom of the bucket, it would affect volume on it's mass, and the weight would have no affect.

The boat is floating, and displacing it's own weight.
The bridge is handling the same amount of weight regardless if there is a boat in transition.

[DAREDEVIL]

Whats heavyer 1000 liter water or 1ton of steel ????

[Wobble]

Whats heavier 1000 liter water or 1ton of steel ????

1000 litres of fresh water weighs more than a "short ton" but less than a "long ton" or a "metric ton"

[Expensive Date]

I am emailing Reggie Fountain he will know.

[Tom A.]

LOL,,are u crazy ???? ofcoarse it will weigh less in that moment...or do u think birds don't weigh anything ???? HAHA

Actually, I saw a Mythbusters episode on this recently and that is not true. With the bird situation, different from the boat displacement, the birds create lift by flapping their wings. The lift created by the wings creates the same downforce pressure as their weight. This down force in psi negates their technical weight but creates the same weight in psi as measured on a scale.
As for cargo bumping loose and into the air, yes the trailer will be lighter for that split second on a scale (if you could actually scale it). A negative g scenario is created by the upward motion same as when we launch off a wave or ride a roller coaster. On the flip side when we (or the cargo) lands, it will weigh heavier based on the impact or positive g's.
Wow I didn't realise I paid that much attention in physics class.... of course some of this may be clouded from too many years of Jack Daniels!

[DAREDEVIL]

1000 litres of fresh water weighs more than a "short ton" but less than a "long ton" or a "metric ton"

Then i guess the school i went to in germany has it all wrong.
1 liter of water weighs 1 kg , 1000 kg = 1 metric ton !!!!????

[DAREDEVIL]

Actually, I saw a Mythbusters episode on this recently and that is not true. With the bird situation, different from the boat displacement, the birds create lift by flapping their wings. The lift created by the wings creates the same downforce pressure as their weight. This down force in psi negates their technical weight but creates the same weight in psi as measured on a scale.

WOW,,,really ,,now thats freak'n funny. But if they say so i guess its true.

OHHHHH,,,wait a minute,,the bird situation in the truck was diffrent,,,he said if the truck would go over a hump and the birds would fly up because of that,,,,,not flapping theyr wings. LOL

[Wobble]

Then i guess the school i went to in germany has it all wrong.
1 liter of water weighs 1 kg , 1000 kg = 1 metric ton !!!!????

that is an approximation that is only true at 4* Celsius. As water increases in temperature it gains volume and weighs less per litre. Also true if it freezes

http://www.simetric.co.uk/si_water.htm

[DAREDEVIL]

that is an approximation that is only true at 4* Celsius. As water increases in temperature it gains volume and weighs less per litre. Also true if it freezes

http://www.simetric.co.uk/si_water.htm

intresting !!! But i was close.

Hey ,,i live in FL...i like my water cold.HEHE

[HaxbySpeed]

. If you fill your plastic cup to the very top and then dump in your quarters the water will overflow and what's left with the quarters will weigh exactly the same as it did without them..

Volume, mass, blah blah blah... Clearly I've been drinking too much Jack. If the quarters weighed the same as the water they displaced then they wouldn't sink to the bottom.. The quarters in the bucket isn't an accurate comparison to the swing bridge deal though because it only picks up things that float. If you put a little boat in a bucket that's filled to the top, then put your quarters in the boat the water that is spilled out will weigh the same as the quarters. The bucket will then weigh the same as it did without them. I spent the last hour hitting myself in the face while repeating "you are so stupid" I feel better now..

[MetalBrosRacing]

Yet another thread that hurts my head.

[DAREDEVIL]

Yet another thread that hurts my head.

LOL

By the way,,,WHO CARES ,,, IT WORKS !!!!!!