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by Ron Kurtus

A total of 94 comments and questions have been sent in. They are listed according to date.

## List of next 10 letters

### Country

Fluids Why are soft drink botles not filled completely? india

Fluids Measuring water pressure in a swimming pool USA

Fluids Would the ocean rise? USA

Floating Density of a floating person USA

Fluids Density of the water in kg/ml maldives

Pressure Liquid pressure with different shapes USA

Fluids Is density proportionate to pressure? maldives

Fluids Fluid pressure increases with density Maldives

Floating Will hydrogen balloon go up faster or slower? New Zealand

Density Density of piece of metal USA

Next 10

First 10 letters

## Why are soft drink botles not filled completely?

Topic: Fluids

### Question

November 10, 2005

i recently gave my physics examinaion and wanted to know the answer of -why are soft drink botles not filled completely?
is it to prevent the bottle from blasting because of the expansion of carbondioxide in it by giving the expansion some space
or is it because of anomalous expansion of water present in the soft drink

prabha - india

8889

The pressure inside the bottle would prevent the CO2 from leaving the water solution. Once the bottle is opened, the gas is released from the liquid. So, that would not be the reason for the bottles not to be filled.

If the bottle is heated, the water will expand. If there is a gas space in the bottle, it will be compressed with the expansion. If there is no space, the expansion could burst the bottle.

## Measuring water pressure in a swimming pool

Topic: Fluids

### Question

October 25, 2005

Can you make a valid science project that has to do with the relationship between water pressure and depth by doing the following?:
Diving down to various depths in various swimming pools with a pressure gauge in order to measure pressure

Erin - USA

8692

If you have access to a pool, you could make the measurements. There is no need to use different pools. That wouldn't achieve anything.

I'm not sure where you could get a pressure gauge to use under the water. You need to get one to use for the experiment.

You might combine a couple of principles to make the experiment more interesting. Suppose you brought a balloon under water and measured its diameter at different depths. The pressure of the water should compress the air and make the balloon slightly smaller.

## Would the ocean rise?

Topic: Fluids

### Question

September 18, 2005

what if everyone on earth went into the ocean at the same time. would the oceans water level rise.

chris - USA

8171

Any time you put something in the ocean the level rises a tiny bit, according to the volume of the object. If everyone went into the ocean, that would be a large enough volume that the level would rise considerably.

## Density of a floating person

Topic: Floating

### Question

September 14, 2005

This question was on a Physical Science Test of mine. A vacationer floats lazily in the ocean with 80 percent of his body below the surface. The density of the ocean water is 1.025kg/m3. What is the vacationer's average density? Could you help explain how to find this answer.

Jessied - USA

8117

The density of an object is its mass divided by its volume. The vacationer's density is D = M/V. The density of the water he displaces is 1.025 = M/v, where v is the volume of the water he displaces and M is both his mass and that of the water displaced.

Since 0.8V is the volume of the water he displaces, 1.025 = M/0.8V and D = 0.82kg/m3.

## Density of the water in kg/ml

Topic: Fluids

### Question

August 29, 2005

can we find the density of the water in kg/ml?

aishath - maldives

7925

The density of water is defined as 1 gram / cubic centimeter which equals 1 kg / liter.

1 kg/l = 1000 kg/ml, since 1000 ml = 1 liter.

## Liquid pressure with different shapes

Topic: Pressure

### Question

August 19, 2005

If you have liquid contained into three differently shaped containers, for example a conical container, a squared container, and a cylindrical one, each one with a tap or a valve at the bottom to allow the liquid to escape when the valve is opened, and the containers are all filled with the liquid up to the same height, how different would the pressure be at the valve? Would the pressure be the same, considering that the heights of the liquid are the same, or due to the different shape of the containers, the pressure would be different?
Gerardo

Gerardo - USA

7826

The pressure is only dependent on the depth of the liquid. The container could be any shape. Also, at a given depth, the pressure is the same in all directions.

## Is density proportionate to pressure?

Topic: Fluids

### Question

July 25, 2005

how to carry out an investigation to prove that desity of the liquid is proportional to the its pressure?

aishath - maldives

7622

A liquid does not have a pressure. The affect of gravity on a liquid creates a pressure at a given depth. You must be clear how you define these things.

The density of a liquid is proportional to its mass. It is mass divided by volume.

For a given volume, the greater the density the greater the pressure at a given depth. Thus the pressure at a given depth in a liquid is proportional to the density. Not the other way around.

You can use a pressure meter at some given depth to prove this.

## Fluid pressure increases with density

Topic: Fluids

### Question

July 25, 2005

I want investigate that the pressure increases in the water along with its density.so i take freshwater and salt water to prove this investigation.so i want some help to do this investigation.

aishath - Maldives

7619

You must be exact in defining what you want to do, when stating an experiment. I assume you are talking about the pressure due to the effect of gravity on the liquid. This is the water pressure at a given depth.

A simple way to do this experiment is to take a bucket or metal can and punch a small hole about 1/3 from the top. First fill the can with pure water and measure the distance the water squirts out of the small hole. Then repeat that with salt water.

Note that the higher the can or deeper the water, the more pressure and the further the water will squirt. Also, a small hole works better than a hole that is too big. You can use a nail to punch a hole in the can or bucket.

## Will hydrogen balloon go up faster or slower?

Topic: Floating

### Question

July 9, 2005

A ballon is filled with a hydrogen gas until it just starts to fly. What will happen to its speed if the volume of the gas is reduced? Will it go faster or slower? Explain why?

hitesh - New Zealand

7505

If you put more hydrogen into the balloon, it will get larger and take up more space. But the hydrogen is lighter than air, so it should go up faster. But at a certain point in filling it, the pressure of the balloon makes the hydrogen more dense, so it will then go up slower.

## Density of piece of metal

Topic: Density

### Question

June 7, 2005

A 6kg piece of metal displaces 2 liters of water when submerged. What is its density?

Tonja - USA

7198

Density = mass / volume = 6/2 = 3 kg/L

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