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Answers to Readers' Questions on Physical Science:

Pressure

The following 25 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• What is the difference between force and pressure?
• Want information on pressure measurement
• Calculating pressure
• Why does a being hit with a cane cause more pain?
• Why is a sharp knive more painful than a dull one?
• 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

Next 10

What is the difference between force and pressure?

Question

July 1, 2010

what is the difference between force and pressure?
show some pictures to show it and illustrations.

Aditya - India

20001

Answer

Force is how hard an object or material pushes on another. Pressure is the force divided by the area in contact.

For example, if you push on the door with your hand, you are applying a force on the door. Units of measurement can be in newtons.

The pressure you are applying is the force divided by the area of the palm of you hand. Pressure would be in newtons per square centimeter.

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Want information on pressure measurement

Question

June 2, 2010

Pressure Measurement Instrumentation

hassan - Libya

19828

Answer

There are numerous devices that measure pressure. Information on such devices can be seen at:

http://en.wikipedia.org/wiki/Pressure_measurement
http://www.sensorsone.co.uk/
http://www.omega.com/pressure/psc.html

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Calculating pressure

Question

May 23, 2010

If I want to calculate the pressure, say a cube excerts on the ground... The cube measurements are 3x3 (for the face) and x3 (for the height), and the force applied was 15N. Would I have to times 15 by 9 or 15 by 28? In other words do I have to times the force by the area only on the floor or the area of the whole cube?

I think it may only be the area on the floor but my physics teacher marked my work as correct on a question like this and I had multiplyed the force by the WHOLE area of the 3D rectange cube thing, not the face. So it got me confused, maybe he just ticked it because he was in a rush and wasn't marking properly?

Thanks, hope this makes sence. I have a test tomorow so I would really appreciate a quick reply.

Lydia - UK

19776

Answer

Pressure is force times the area in contact with the other surface.

Since a newton relates kilograms and meters, I assume the 3x3x3 cube is in meters. Thus, the area in contact would be 3x3 = 9 square meters. So the pressure would be 15 x 9.

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Why does a being hit with a cane cause more pain?

Question

December 9, 2009

explain why a person beaten with a cane experiences a greater pain than that of the palm?

Jennifer - Ghana

18814

Answer

Pressure equals force divided by surface area (P = F/A). If you have a small surface area, the pressure will be much higher than that with a large surface area for the same force.

The area striking you with a cane is much less than with the palm of the hand, thus there is greater pain-causing pressure from a cane and from the palm.

Also with a cane, you are swinging at from your hand, so it is striking that person with a much higher velocity and even more force and pressure that if simply hit with a hand.

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Why is a sharp knive more painful than a dull one?

Question

November 22, 2009

why is it painful when you are hit by a sharp knife but not when hit by a knife with out sharpness

cabdirisak - Norway

18720

Answer

Pressure is force divided by area. When the contact area is smaller for the same force, the pressure is greater.

The contact area of a sharp knife may be 5 less than a dull knife. That means for the same force, it could cut the skin or cut into some item.

Even if the knife does not cut the skin, the sharp knife exerts more pressure and thus causes more pain.

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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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