mechanical aptitude

[Neil]

Originally Posted by jambutty

Nothing to say about:
Re your analogy of the fireman’s water pump. You can still pump water out of a sealed container where air is prevented from replacing the removed water. It takes more effort but it can still be done. Therefore the water is sucked out.

How many times do I have to say, the movement is from an area of high pressure to an area of low pressure?

[Neil]

Originally Posted by jambutty

Basically it amounts to - when you remove air or a liquid from somewhere you suck it out. When you put air or liquid into a container of some sort you pump it in.

In fact the title of the article is interesting because, as it mentions, a vacuum cleaner will not work on the moon.

Here is a quote from this teaching website Workbench: You Can’t Vacuum the Moon

Your comments about liquids are also incorrect. It is the pushing force of gasses that cause the movement of liquids in all the cases that have so far been mentioned. Unless of course you are pressurising the liquid then it too will move from an area of high pressure to one of low pressure ( a hose pipe would be a simple example)

If you don't want to believe what it says that is fine by me. I am surprised by the way you let your stubbornness make you appear ignorant to the physics in question. I must have been wrong when I assumed you to be an intelligent man.

* Any situation in which suction seems to be apparent can now be explained properly.
* The expansion of sealed snack bags or the explosion of shampoo in suitcases of airplane passengers can be explained by the changes in air pressure

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Science Concepts

Gases exert a pressure through the collective impacts of their atoms on the surface of an object or container. Because of this, pressure is always a positive value. In other words, gasses can only push on things, never pull on things. The lowest pressure achievable occurs when there are no atoms around, such as in outer space.*

Any time something seems to be pulled by suction, the actual cause must be explained by using pushing forces of gasses. Suction is better defined as a net pushing force in a particular direction due to the differences in two gas pressures.

This can best be understood by looking at several examples which can also be used in class discussion:

* Straws: When you “suck” on a straw, you actually expand the volume of gas on one side of the liquid (the side connected to your mouth). By expanding the volume of the gas inside the straw, you spread the atoms out, resulting in a lowering of pressure inside the straw. It is the outside air pressure that is also pushing on the liquid in the straw which pushes the liquid up the straw. You don’t pull the liquid into your mouth, you lower the internal pressure to allow the outside pressure to push the liquid up the straw.
* Vacuum Cleaners: Vacuum cleaners work by creating a lower pressure just inside the opening which touches the floor. By creating a low pressure inside the machine, higher air pressure in the room pushes its way into the vacuum cleaner, taking the dirt with it. Because there is no, or very little, atmosphere on the moon, you can’t create a lower or higher gas pressure inside and outside the machine, so you can’t “suck” any dirt up from the ground. Nothing happens when you turn on a vacuum cleaner on the moon. (You wouldn’t even hear it because some substance, usually air, is necessary to transmit sound waves.)

*Actually, there are some atoms in outer space, but they are so few and far between that the pressure is almost zero there.

Naive Conceptions

• Suction is a pulling force.
In almost any case where the word suction is used, it is referring to some pulling force. For example, sucking a drink up a straw, using a vacuum to suck up dirt, astronauts being sucked out into space if a hole in their ship occurs. In every one of these cases the cause of the suction is a difference in gas pressure between two regions of space. Gas under higher pressure will push its way to an area of lower pressure. A straw works because the air pressure inside your mouth is less than the air pressure outside which pushes the liquid up the straw. A vacuum cleaner creates a region of low pressure inside so that air under higher pressure will push its way into the vacuum cleaner. Air in a spaceship is under high pressure (compared to outside the ship) and pushes its way out of the hole in the ship. There is no such thing as a pulling force of suction - only pushing forces.

[jambutty]

No one ever stated that you could vacuum on the moon. But then that is what some people do, throw in red herrings to confuse the issue.

But you can pump water on the moon if there is enough of it to pump before it evaporates. Which totally destroys your theory that it is air pressure on the surface of the water that forces the water through a pump and not the pump sucking the water away. There ain’t no air on the moon.

And you have conveniently forgotten to challenge the ‘air is sucked out of a bell jar by a vacuum pump’ statement. Could it be that there is no challenge to make and you cannot bring yourself to admit that air and water can be sucked out from containers as well as being pumped out?

However if the best that you can do is insult people there is no more to be said.

Verb sap!

[Neil]

Originally Posted by jambutty

However if the best that you can do is insult people there is no more to be said.

Insult you, I actually paid you a complement.

I have given you a link explaining how suction really works but you choose to ignore it. What else can I say to that? Unfortunately you appear unable to admit when you are wrong, I can say that is a quality that I do poses and if you took of your blinkers and actually read the link I posted you should now understand why I have been saying what I have all along. Unless of course my Physics A level teacher was also wrong