# The Naked Scientists Forum

### Author Topic: Effect on Buoyancy  (Read 7741 times)

#### Narayana

• First timers
• Posts: 3
##### Effect on Buoyancy
« on: 20/03/2004 11:17:36 »
Let me explain my problem in simple numericals.

unit weight of water = 1030 kg/cu.m

Total Volume of hollow sphere = 1 cm.m

Total weight of Sphere = 1200 kg

Net downward weight = 1200 - 1030 = 170 kg

In this case sphere will settledown.

When water is mixed with sediments, the density of water is going to increase,

unit weight of water = 1400 kg/cu.m (approx.)
(as it is mixture of sediments and water)
( please don't concentrate on numbers, see the concept)

Total Volume of hollow sphere = 1 cm.m

total weight of Sphere = 1200 kg

Net downward weight = 1200 - 1400 = - 200 kg

In this case sphere will float.

The main question what i want to ask from these problems is,

when soil particles present in water, it is going to increase the desity of water. Does it increase the Buoyancy effect also?
if, so why?

Does the Soil particle present in Liquid behaves like a liquid?

waiting for replies

Thanking you,

Faithfully
Narayana

K.NARAYANA
BANGALORE
INDIA

#### qpan

• Sr. Member
• Posts: 260
##### Re: Effect on Buoyancy
« Reply #1 on: 20/03/2004 11:34:55 »
i'm not totally sure on this- but i thought that only dissolved substances change the density of water. Therefore, only the soil which had become dissolved in the water will add to the effect of bouyancy- the solid particles of soil (no matter how small) will not contribute to the density of the liquid due to still being a solid and therefore unable to exhibit the liquid property of upthrust.
So the soil particles do not behave like a liquid, but the small amounts which dissolve do behave like a liquid.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

#### Ylide

• Moderator
• Hero Member
• Posts: 905
##### Re: Effect on Buoyancy
« Reply #2 on: 22/03/2004 16:01:59 »
I have a couple things to add:

First, Narayana, in your initial problem, the density of water is not going to increase because when you add sediment, the density of the "mixture" will increase.  It's important to make that distinction.  Also note that the volume of the mixture will increase with the added material so your calculations should account for that.

With that in mind, the density of the water essentially the same.  There may be some very minor force exerted by the swirling particles, but those are eventually going to settle if they're insoluble.  Even a very small amount dissolving will not have a significant effect on density.  For instance, if 1 gram dissolves in 1 liter of water, the density has changed from 1000g/L (depending on temperature) to 1001g/L.

If you eventually add enough sediment to change the state of the water from a liquid to a colloidal suspension (i.e. mud) then you're going to start seeing sigficant effects because you're no longer dealing with water.

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#### Narayana

• First timers
• Posts: 3
##### Re: Effect on Buoyancy
« Reply #3 on: 23/03/2004 06:44:27 »

Thank you cannabinoid,

I want to extend the problem, a little.

Here My point of interest(as you mentioned)is Buoyancy in mud Slurry

i.e

If I add enough sediments to change the state of the water from a liquid to a colloidal suspension (i.e. mud) then

what is the effect of this slurry on Buoyancy ?

whether it is going to increase the Buoyancy or remains same          (compared with Buoyancy in water).

Faithfully,

K.NARAYANA
BANGALORE
INDIA

#### qpan

• Sr. Member
• Posts: 260
##### Re: Effect on Buoyancy
« Reply #4 on: 23/03/2004 22:08:35 »
Well, the effect of bouyancy is caused by the displacement of water.

If you have a tank of water and you hold a ball under the surface of the water and let go, 1 of 3 things can happen.

1.Nothing. If the ball's weight is exactly equal to the weight of the water it displaces (i.e. its own volume of water), the ball will stay in the same place.

2.Float. By archimedes' principle, the amount of upthrust experienced by an object is exactly equal to the volume of water it displaces. If the ball's weight is less than the weight of water it displaces, the upthrust will be greater than the weight and the ball will float to the surface. Once at the surface, the proportion of the ball which is submerged will depend on the weight of the ball- the water displaced by the ball while floating will be exactly equal to its weight.

3.Sink. If the ball is heavy enough, the upthrust will be less than the weight and the ball will sink.

Therefore, using archimedes' principle for a mud slurry, the liquid will be far denser than water and so, every 1 cm^3 displaced will generate a greater amount of upthrust than 1 cm^3 of water.

So, to answer your question, the bouyancy will be far greater in mud than in water.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

#### The Naked Scientists Forum

##### Re: Effect on Buoyancy
« Reply #4 on: 23/03/2004 22:08:35 »