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Answers to Readers' Questions on Physical Science:

Pressure

The following 20 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• What is the name of lines of equal pressure?
• What is pressure?
• Is pressure a scalar or vector?
• Using a pressure cooker at high elevations
• Would like answers to quizzes
• Pressure of falling body at impact
• Would a camel's foot be low or high pressure?
• Why don't we feel atmospheric pressure on our skins?
• When is water pressure equal to air pressure?
• Discuss the importance of measuring pressure and flow

Next 10

What is the name of lines of equal pressure?

Question

July 3, 2009

what is the name of lines of equal pressure?

sue - UK

17974

Answer

Isobars. "Iso" means equal and "bar" means pressure (like in barometer).

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What is pressure?

Question

May 26, 2009

hi sir,how are you?

some difficulties.

what is pressure?

MUHAMMAD - Pakistan

17806

Answer

Pressure is force over a given area. Pressure = Force / Area. If you press on something with a force, it is spread over the area with which you press.

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Is pressure a scalar or vector?

Question

August 14, 2008

Q. What is the nature of pressure, whyther it is scalar or vector? please explain if possible?

farooq - Pakistan

16357

Answer

A vector quantity means that it is in a direction, while a scalar quality is just a numerical value.

If you push on a door, you are applying a force and pressure in a given direction. Thus that pressure is a vector. When you put your hand under water, the water applies pressure on each point of your hand inward. So again pressure is a vector.

Something like area has no direction, so it is a scalar value.

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Using a pressure cooker at high elevations

Question

May 9, 2008

why we use pressure cooker on hilly areas.atmospheric pressrue increas or decreas on hieght.

bushra - Pakistan

15912

Answer

As you go to higher elevations, the air pressure or atmospheric pressure decreases. That means that the relative pressure inside a pressure cooker would be greater than it would be at lower elevations. Thus, the pressure cooker should work better at higher elevations.

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Would like answers to quizzes

Question

January 9, 2008

Hello my child has been missing alot of science homework and I would like to quiz them with these questions to see if he can handle them, I would really appreciate if you gave me the answers to the questions so I could give him the quiz by Friday, Thank you have a great day!

Cindy - USA

15092

Answer

We have online graded tests on some topics at:
http://www.school-for-champions.com/tests.htm

For the mini-quizzes, you can click on the buttons to see if the answer is right or wrong. He should be able to do that himself.

I hope he catches up with his homework.

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Pressure of falling body at impact

Question

December 22, 2007

Is the pressure of a free falling body on a surface area at the moment of collision different from its pressure on this surface area when it is at rest?

Thank you for this wonderful website.

Mohammed - Egypt

15012

Answer

The pressure on the bottom surface area of an object at rest is its weight divided by the bottom surface area. The weight or force at rest is the mass times the acceleration due to gravity: F = mg.

But the force on impact of a falling body is the mass times the deceleration of the mass. The value for the deceleration (negative acceleration) depends on the speed at impact and how elastic the material is.

Note too that if the body is falling in air, there is an added pressure on the surface due to air resistance.

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Would a camel's foot be low or high pressure?

Question

November 27, 2007

Would a camels foot be low or high pressure?
would a block of wood on ice be high or low pressure?
would ski's be high or low pressure?
Thankyou

- Scotland

14866

Answer

Pressure due to gravity is weight divided by area. A camel's foot would have the pressure of its weight divided by the area of the foot on the ground.

The higher up you go, the less air there is above you, and thus the air pressure drops.

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Why don't we feel atmospheric pressure on our skins?

Question

November 5, 2007

The atmospheric pressure is 101300 newtens per square meter which means 10.13 newtens per square cm. If the accelaration due to gravity is 9.8 m/s^2. Does this mean that the atmospheric pressure is equal to the pressure caused by a cube of mass 1.034 kg and area of 1 square cm? If this is true, Why don't we feel the atmospheric pressure on our skins?

Mohammed - Egypt

14709

Answer

Our bodies have an internal fluid pressure that is equal to the atmospheric pressure. Thus, we don't notice it. Likewise, when you swim under water, your body adjusts the internal pressure in a few seconds. But a deep-sea diver has to be careful when coming to the surface to allow his internal pressure to adjust to the lower atmospheric pressure at the surface. Otherwise, he could get what is called the bends, which is very painful.

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When is water pressure equal to air pressure?

Question

August 8, 2007

Dear sir,
please solve this question:
At what depth below the surface of water will pressure be equal to the atmospheric pressure? The atmospheric pressure is 10N cm-2, density of water = 1000 kg m-3,g= 9.8 m s-2.

ankit - India

14174

Answer

Water pressure equals the weight of the water above a certain point divided by the area plus the air pressure at the surface of the water. Thus the point where the water pressure is the same as air pressure is at the top surface of the water.

Thoughts, if you'd do not take in consideration the effect of air pressure on water pressure, you can determine the water pressure as they weight per unit area that is equal to the atmospheric pressure.

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Discuss the importance of measuring pressure and flow

Question

March 22, 2007

critically discuss the importance of measuring pressure,flow,level and teperature in industry

mvelo - SA

13412

Answer

It depends on the industry. If they are transporting liquids such as fuel, it is necessary to monitor it.

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