River Over A River

[Windsor]

I posted this in another thread but did not elaborate, and likely most viewers might have missed it as it was buried in the thread. So here it is again.

Water Bridge in Germany.... What a feat!
Six years, 500 million euros, 918 meters long.......now this is engineering! This is a channel-bridge over the River Elbe and joins the former East and West Germany, as part of the unification project. It is located in the city of Magdeburg, near Berlin. The photo was taken on the day of inauguration.

To those who appreciate engineering projects, here's a puzzle for you armchair engineers and physicists.
Did that bridge have to be designed to withstand the additional weight of ship and barge traffic, or just the weight of the water?

[/IMG]

[/IMG]














Answer: It only needs to be designed to withstand the weight of the water!
Why? A ship always displaces the amount of water that weighs the same as the ship, regardless of how heavily a ship may be loaded.

 

[middaydog]

Wah leh! Before I scroll down my answer oreddy correct

 

[Windsor]

Wah leh! Before I scroll down my answer oreddy correct

Haha you choose either yes or no only? Or you have the reason why your choice is correct?

 

[middaydog]

My secondary school teacher taught me physics , ok

 

[Windsor]

My secondary school teacher taught me physics , ok

Not trying to insult you lah. I myself bad in physics and had to google for the answer. Just curious, as the explanation given is right but there is another question that follows after.

 

[Zombie]

if the bridge is designed to withstand just the weight of water, i think it will collapse whenever a heavy ship sinks...

 

[Windsor]

if the bridge is designed to withstand just the weight of water, i think it will collapse whenever a heavy ship sinks...

No it will not as the water displaces the weight of the vessel/s. It is not actually a river but a man-made canal which is only 918 metres long. The 2 locks will operate to ensure water flows in and out to compensate the weights by releasing or pumping the water at both ends, so the water level remain constant.

 

[Zombie]

No it will not as the water displaces the weight of the vessel/s.

this is the law of floatation... only when it floats..

if there is a hole and the ship sinks and fully submerged, the displaced water returns to fill the void... the additional weight would be the weight of the steel less the weight of water (for the volume of steel)

 

[Windsor]

this is the law of floatation... only when it floats..

if there is a hole and the ship sinks and fully submerged, the displaced water returns to fill the void... the additional weight would be the weight of the steel less the weight of water (for the volume of steel)

Yes, but the locks are working to release the water to compensate for the additional weight.

 

[Zombie]

sure.. there are safety measures...
anyway it is a beautiful structure...

 

[scroobal]

The way it works is that displaced water must leave the bridge either thru the channels or valves. If not both the water and ship weight must be factored in. I am sure the ship weight was factored in as continous pumping of water would be unnecessary operating costs. I am sure the the locks do not do this function.

No it will not as the water displaces the weight of the vessel/s. It is not actually a river but a man-made canal which is only 918 metres long. The 2 locks will operate to ensure water flows in and out to compensate the weights by releasing or pumping the water at both ends, so the water level remain constant.

 

[Windsor]

sure.. there are safety measures...
anyway it is a beautiful structure...

This reason was given by wiki why they need to do it this way.



The Elbe-Havel and Mittelland canals had previously met near Magdeburg but on opposite sides of the Elbe, which was at a significantly lower elevation than the two canals. Ships moving between the two had to make a 12-kilometre (7.5 mi) detour, descending from the Mittelland Canal through the Rothensee boat lift into the Elbe, then sailing downstream on the river, before ascending up to the Elbe-Havel Canal through Niegripp lock. Low water levels in the Elbe often prevented fully laden canal barges from making this crossing, requiring time-consuming off-loading of cargo.[SUP][2][/SUP]

[/IMG]

 

[Unrepented]

Same volume but different density how? I mean how do they know what is the additional weight of the goods if the ship sinks? Just curious.

Yes, but the locks are working to release the water to compensate for the additional weight.

 

[Windsor]

The way it works is that displaced water must leave the bridge either thru the channels or valves. If not both the water and ship weight must be factored in. I am sure the ship weight was factored in as continous pumping of water would be unnecessary operating costs. I am sure the the locks do not do this function.

You are right it is a series of pumps and valves.

 

[Windsor]

Same volume but different density how? I mean how do they know what is the additional weight of the goods if the ship sinks? Just curious.

Archimedes Principle only applies to the volume but not density of the object immersed in water. I assume that there are safety measures in place that will ensure nothing like it will happen and if it does there are safety procedures to overcome it.

 

[Seee3]

Same volume but different density how? I mean how do they know what is the additional weight of the goods if the ship sinks? Just curious.

If my physics teacher is correct, the total weight of a ship cannot be more than the weight of the water that it displaced. Otherwise the ship cannot float. Therefore, the total volume of a ship is always more than the water that it displaced.

However, when it sinks, the air escapes and your concern becomes valid. I guess they must have some safety factor added to the calculation for the bridge to withstand the additional weight.

 

[Conqueror]

Cao Chong And The Elephant

Cao Chong 曹冲 (196–208) was a son of the late Han Dynasty warlord Cao Cao. He was renowned as a child prodigy, having the intelligence of an adult at the age of five. He is best known for his ingenious method of weighing an elephant using the law of buoyancy. Considered by Cao Cao as the successor, however Cao Chong died of sickness at the age of thirteen.


ao Chong was born the eldest son of Cao Cao and Consort Huan. According to the Records of the Three Kingdoms by Chen Shou, Cao Chong had the intelligence of an adult around the age of five and six. On one occasion, the southern warlord Sun Quan sent a gift of an elephant to Cao Cao, who wished to know the animal's weight. No one could think of a method but young Cao Chong had an ingenious idea. Somewhat similar to Archimedes' solution to the legendary Problem of the Crown, Cao Chong asked to have the elephant loaded onto a boat, on which the water level was marked. The elephant was then replaced with smaller weighable objects until the boat was submerged to the same level. The weight of the elephant could then be found out by summing up the weights of all the objects. According to Joseph Needham, although no official treatise in the likes of Archimedes' principle was ever written regarding buoyancy in ancient China, there were observational precedents of it in the Rites of Zhou, compiled and edited during the early Han Dynasty (202 BCE - 220 CE).

Joseph Needham states:

Empirical use, of course, was made of [Archimedes'] principle, as in the floating of arrows and vehicle wheels in water by the [Zhou] and Han technicians, in order to determine their equilibrium and add or remove material accordingly.

In another incident, Cao Cao's saddle was chewed through by rodents. The storekeepers were in great fear for their lives as laws were strict during those times of war. When Cao Chong learnt of their plight, he took a knife and cut holes in his clothings as if rats had bitten through them. He then went to see his father and complained that he feared ill luck brought by the rat bites. Cao Cao consoled him, saying it was only a superstition. Cao Chong then told Cao Cao of the damaged saddle. Cao Cao laughed and said, "Even when my son's clothings were just by his side, they could not be spared from the rats, let alone the saddle in the store." The storekeepers were then pardoned.

Cao Chong would often review cases of indicted criminals for any injustice. His intelligence and benevolence had won the love of Cao Cao, who often voiced his intention to make him his successor. Cao Chong died, however, in 208 at the age of thirteen. Cao Cao accordingly said to Cao Pi, his ultimate successor: "This is my misfortune, but your good fortune."

In 221, Cao Chong was posthumously given the title of Marquis Ai of Deng (鄧哀侯), and was ultimately elevated to Prince Ai of Deng (鄧哀王) in 231. He was succeeded by his nephew Cao Cong (曹琮) since he was without his own heir.