chemsitry 101

Question

When an ordinary piece of steel is put under pressure, the steel compress; that is, its volumes slightly decrease.

Question,

What does it mean " pressure " here ?

What does it mean " compress " here ?

What does it mean " volume decrease " here ?

Thanks

CalifJim · Accepted Answer

Somebody needs to get a good dictionary!

Hold a raw egg in your hand. Close your fist on it as tight as possible. You are putting the egg under pressure. As you squeeze harder and harder you are putting more and more pressure on the egg. If you put enough pressure on the egg, it will break!

CJ
[2]

BW2/3 · Answer

Thank for the explanation, and I look up at the dictionary.

compress ( reduce size )

volume ( amount )

What are those two sentences mean ? I could not picture it myself. When a steel under pressue and it compress ( of what ) and its volume ( amount of space ) decreases?

Once again, thank you CJ.

CalifJim · Answer

A big bottle holds more liquid than a small bottle. The big bottle has a greater volume. It contains more space. The small bottle holds less liquid because it has a smaller volume. The small bottle has less space where you can put the liquid. It has less volume.
A big box holds more objects than a small box. The big box has a greater volume. The small box holds fewer objects because there is less space in the small box. The small box has a smaller volume.

Imagine a big, wet sponge.
Squeeze it hard. Press hard on it to get the water out of it. Now it is compressed. You have compressed it -- made it smaller. When you make it smaller it will fit into a smaller amount of space. When you put pressure on it by squeezing it, it becomes smaller in size. You have compressed it. You have made it smaller. It can fit into a smaller amount of space when it is compressed. It can fit into a smaller volume when it is compressed.

If you take a piece of steel instead of a sponge, you can do the same thing. You will need a powerful machine to compress the steel, and the steel will not become very much smaller, but the idea is the same as for the sponge.

CJ

Goodman · Answer

Hi BW,

I like to add a little to CJ's explanation. .....

A locomotive operates on the principle of water pressure. When the water in the boiler is brought to boiling point, the water becomes pressurized steam. In a contained environment, the steam turns into positive pressure which is used to pushes the pistons attached to the wheels of the locomotive. Technically, material can be compressed by positive or negative pressure. However, most people think of pressure as being positive. In reality, we can use negative pressure to compress. Try this: put a pillow in a leak-proof large plastic bag and insert a vacuum cleaner tube to the opening of the bag. Tightly hold the bag over the tube and turn on the vacuum cleaner. Observe the pillow in the bag. First the bag will start shrinking followed by the pillow. The reason is because the air in the pillow and the bag are being sucked out to the vacuum cleaner. When all the air is removed from the bag, the pillow will be reduced to about 25% of the original size. We can acutually use this method when we pack our lugguage to reduce the volume of out clothing. You will be amazed how much lugguage space is created by removing the air our of our clothes.

Nowadays, most of the inexpensive furniture is made with “compressed” wood (or commonly called particle board). This procuct is made by utilizing the wood scrap which is uniformly reduced to a consistancy of wood shaving. Then a industrial adhersive call "Epoxy" is added to form a mixture. Then the wood shaving and adhersive mix is processed in a heat abd pressurized environement to give the end product strenth. Positive pressure is measured in PSI (Pound per Square Inch). Commercially, high pressure compression is used to strengthened most of materials.

Also, the garbage trucks use Hydraulic compression to reduce the volume of garbage collected. That's the only way a track can collect garbage from so many houses.

BW2/3 · Answer

Goodman,

Interesting. I enjoyed reading it.

BarbaraPA · Answer

By the way, as a grammatical correction to the original post:

When an ordinary piece of steel is put under pressure, the steel compresses; that is, its volume[no s] slightly decreases.

Goodman, if you put the steel under enough pressure, doesn't the temperature also rise? The expression PV/T comes to mind, but I don't know from where...

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