Can't Figure This Out

[Horn_Spanker 524]

Watch this video from 8:30 to 9:40.  Can't understand how displacing water creates weight?  Googling, I find underwater weighing as in calculating body fat, but there the person is being weighed, not the water.

https://youtu.be/M1OKYCQDOXU?si=TJkT1Dy13LixPGc-

 

[MonkeyDoughnut 10356]

On 8/3/2024 at 7:14 PM, Horn_Spanker said:

Watch this video from 8:30 to 9:40.  Can't understand how displacing water creates weight?  Googling, I find underwater weighing as in calculating body fat, but there the person is being weighed, not the water.

https://youtu.be/M1OKYCQDOXU?si=TJkT1Dy13LixPGc-

 

Archimedes principle.  Better explained here

 

 

[SurlyGator 876]

OK, here is where my public school education fails me.  If two objects of identical volume but made from materials of different densities are submerged in water, but both are dense enough to overcome the buoyant force of the water (in other words, they both sink), would the denser of the two displace more water than the less dense object?  I need an example to wrap my brain around that one.

This thread could quickly devolve into an "explain this to me like I'm five" exercise...

[pantone159 719]

1 minute ago, SurlyGator said:

OK, here is where my public school education fails me.  If two objects of identical volume but made from materials of different densities are submerged in water, but both are dense enough to overcome the buoyant force of the water (in other words, they both sink), would the denser of the two displace more water than the less dense object?exercise...

No. They would both displace exactly the same volume of water, the volume of the objects.

If the object is FLOATING, then the weight of the water displaced will equal the weight of the object. So if your two identical objects have a density small enough to float, then the denser one will displace more water (and float lower) than the less dense one.

[SurlyGator 876]

That's what I was thinking, but I couldn't figure out how Archimedes Principle would apply.

[locodos 5393]

7 minutes ago, SurlyGator said:

OK, here is where my public school education fails me.  If two objects of identical volume but made from materials of different densities are submerged in water, but both are dense enough to overcome the buoyant force of the water (in other words, they both sink), would the denser of the two displace more water than the less dense object?  I need an example to wrap my brain around that one.

This thread could quickly devolve into an "explain this to me like I'm five" exercise...

Volume of 1lb of lead < Volume of 1lb of wood 

 

[Horn_Spanker 524]

I understand the displacement from the volume, but my problem is weight.  In my link there is displacement, but the volume of water stays the same.  How can weight be created?

Is height of the water a factor?  

[SurlyGator 876]

16 hours ago, locodos said:

Volume of 1lb of lead < Volume of 1lb of wood 

 

This doesn't really correlate with the question, because wood floats.  Try this comparison:  If you suspended a golf ball with a wire fully submerged in the middle of a container of water, and then did the same thing with a piece of lead the exact same volume as the golf ball.  They would both sink.  I would think they would displace the same amount of water equivalent to their volume, but this principle would suggest that the lead would displace more.

[immamac 43047]

On 8/3/2024 at 7:14 PM, Horn_Spanker said:

Watch this video from 8:30 to 9:40.  Can't understand how displacing water creates weight?  Googling, I find underwater weighing as in calculating body fat, but there the person is being weighed, not the water.

https://youtu.be/M1OKYCQDOXU?si=TJkT1Dy13LixPGc-

 

He's trying to find the density of the button so he can calculate the proper karat value. He weighed the button before and you need to weigh the displacement to understand the density of the object. 

[SurlyGator 876]

So with the button analogy - if you weighed the displacement caused by a 10K gold button and a 24K gold button with identical size and volume measurements, the displaced weight would be different?  I can't wrap my noggin around how this would not be identical due to identical volumes.

[Horn_Spanker 524]

2 hours ago, immamac said:

He's trying to find the density of the button so he can calculate the proper karat value. He weighed the button before and you need to weigh the displacement to understand the density of the object. 

This is my problem, how does displacement create weight?

[immamac 43047]

1 hour ago, SurlyGator said:

So with the button analogy - if you weighed the displacement caused by a 10K gold button and a 24K gold button with identical size and volume measurements, the displaced weight would be different?  I can't wrap my noggin around how this would not be identical due to identical volumes.

Well since that's fucking impossible that maybe your answer. A 24k button and a 10K gold button wouldn't be the same size and volume because that's not how density works. You can't have them be the same size and shape unless one was hollow. 

[ztejas 43537]

23 minutes ago, Horn_Spanker said:

This is my problem, how does displacement create weight?

Because water isn't a zero gravity environment. Say you have a tub of water and you float a bunch of shit on the top of it. The tub will weigh more - but it's not going to weigh what the water weighs plus what the items weigh - because the buoyancy is counteracting gravity. 

Think about paddling a canoe vs dragging that shit over land. One is a lot easier - but they both require force to move. 

Edited August 6 by ztejas

[immamac 43047]

from quora, explanation for you

Quote

I am interpreting the question to mean that we make the reasonable approximations not to consider the density of ambient air, nor variation of the gravitational field. We go through the following steps:

We weigh an open-topped container with liquid in it. Thus, we measure the weight of container plus liquid.

We immerse a body in the liquid. This body has greater density than the liquid, so it is immersed by the effect of its own weight. However, the immersed body does not touch the container, because it is supported by a rope that holds the body above the bottom of the container.

We weigh the container again.

The question then is how the weight that we measure in Step 3 is related to the weight we measure in Step 1. To answer this question, we consider the tension in the rope that supports the body.

In Step 1, while the body is hanging above the liquid, the tension in the rope is the full weight of the body. Then

Tension in the rope +
Measured weight of the container =
Total weight of body + liquid + container.            (1)

This equation is true because everything is supported by either the rope or the scale under the container, so the total weight measured by those two support systems equals the total weight of all three components.

In Step 3, the tension in the rope is reduced by the buoyant force of the liquid acting on the body. (The hydrostatic pressure of the liquid touching the underside of the body is greater than the hydrostatic pressure of the liquid touching the upper side of the body.) However, Equation (1) above remains true, because the rope and the scale under the container are still the only supports for the weight of the three components.

Consequently, the weight measured by the scale under the container increases from Step 1 to Step 3 by the weight of the liquid displaced by the immersed body.

There is a family of interesting physics puzzles involving the effects of objects floating on a body of water that perform various acts, such as melting, shedding jetsam that floats or sinks, or themselves sinking. This puzzle is of a similar sort, and equally interesting. I had not seen this puzzle before, and thank Nemat G. Aziz for posting it.

 

[MonkeyDoughnut 10356]

1 hour ago, Horn_Spanker said:

This is my problem, how does displacement create weight?

Newtons third law - every action there is a reaction.

When something is placed into water, buoyancy is pushing up on the object. The object must in turn push against it. This is the "created" weight.

If you hold a watermelon and submerge it in water it will start to feel lighter to you. The reduction of weight is because of the buoyant force pushing against it. The watermelon obviously doesn't weigh less, but some of the feeling of weight has shifted from you to the scale.

[SurlyGator 876]

5 hours ago, immamac said:

Well since that's fucking impossible that maybe your answer. A 24k button and a 10K gold button wouldn't be the same size and volume because that's not how density works. You can't have them be the same size and shape unless one was hollow. 

What?!?  I'm no nerdz, but I'm smart enough to know you could make an identical sized button out of both 10K gold and 24K gold.  The 24K button would weigh more, but would it displace more water?  I'm thinking no.

[immamac 43047]

43 minutes ago, SurlyGator said:

What?!?  I'm no nerdz, but I'm smart enough to know you could make an identical sized button out of both 10K gold and 24K gold.  The 24K button would weigh more, but would it displace more water?  I'm thinking no.

Did you miss the part where you know the weight and displacement which lets you understand the density. 

You can't make the same weight same sized 10K vs 24K 

You can have 2 similar sized things or one unknown composition and you are solving for the unknown with the things you can measure. 

[SurlyGator 876]

Same weight was never part of the discussion.  The point of the entire confusion is the weight of the water displaced.  I'm saying those two items - though they don't weigh the same - would displace the same amount of water, because they are the same volume.

[jeevsie 3740]

How does the treadmill come into play?

[ztejas 43537]

17 hours ago, SurlyGator said:

Same weight was never part of the discussion.  The point of the entire confusion is the weight of the water displaced.  I'm saying those two items - though they don't weigh the same - would displace the same amount of water, because they are the same volume.

The water displaced doesn't weigh the same. I think that's the crux of the confusion.

[UT_OB1 2225]

On 8/6/2024 at 5:48 PM, SurlyGator said:

Same weight was never part of the discussion.  The point of the entire confusion is the weight of the water displaced.  I'm saying those two items - though they don't weigh the same - would displace the same amount of water, because they are the same volume.

 

On 8/7/2024 at 11:56 AM, ztejas said:

The water displaced doesn't weigh the same. I think that's the crux of the confusion.

[NotActuallyALonghorn 4977]

This is embarrassing.