My high school chemistry teacher said that there is no such thing as a “vacuum,” it’s just a difference in air pressure. But you always hear about the “vacuum” of space, or when something is “vacuum-sealed.” I am not scientifically inclined, so I don’t even know where to begin. Im also not sure if “physics” is the correct flair lol. I was wondering if it could be explained from either side of the argument.
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I think the vacuum of space is called that because there isn’t anything in it. There is nothing to give pressure. Especially in deep space. No gravity, no atmosphere weighing on you of any sort. It’s just empty nothing.
> My high school chemistry teacher said that there is no such thing as a “vacuum,” it’s just a difference in air pressure.
When people say this, what they usually mean is that there is no region or substance that ‘sucks’ the way we intuitively think of a vacuum as doing. Rather, a vacuum is an area of lower pressure, and anything being ‘pulled’ in is actually being pushed by the high pressure fluid on the other side.
So there is such a thing as a vacuum, but the vacuum in and of itself does not have an effect on its surroundings. Instead, it is the high pressure non-vacuum fluids that exert forces.
Vacuum is just a term we use to describe an area that has relatively low pressure or near-zero pressure. Vacuums exist as a lack of pressure in exactly the same way that cold exists as a lack of heat—it’s not a thing unto itself, but it is a useful concept for discussion purposes. That’s probably what your teacher was trying to convey, but if so they did a poor job of communicating it.
This is an issue of two different definitions.
What your teacher means when they say there’s no such thing as a a vacuum is “a thing that sucks things in”
What people mean by “the vacuum of space” is “a region with nothing in it, even air”
Air exerts a pressure. If you have a tube just sitting around, the air on the inside exerts the same pressure as the air on the outside, and nothing happens. If there’s a vacuum in the tube, and thus no air, than there’s nothing pushing away from the tube to counteract the air outside pushing towards the tube. Something near the tube will experience this imbalance, and it’ll look like it’s getting *sucked in* by the vacuum *in the tube*, but really it’s getting *pushed in* by air *outside the tube*. That’s what your teacher means by “there’s no such thing as a vacuum”
It’s because of the difference between theory and real life. A true vacuum has zero pressure– nada. Even interstellar space may see an atom slip into a volume, making it not a theoretically perfect vacuum.
A vacuum is when there’s less particles than normal. A perfect vacuum would be no particles at all.
This means a few things, for instance with pressure, we are used to the atmospheric pressure, and when there’s less pressure than that, we call it a vacuum.
For something to be vacuum sealed it means that the air inside it was removed and it was sealed so new air can’t come in.
In space there’s very very few particles and therefore pressure, so we call it a vacuum.
I think of air like a large jar full of rubber bouncy balls in it. Unlike regular bouncy balls however, they bounce up to the top of the jar just as much as down. Imagine that gravity really isn’t having a big effect at this time.
Now if we squeeze the lid down into the jar, the same number of bouncy balls are in the jar but they bounce and hit the sides of the jar more often because they’re always moving. That’s high pressure. The jar itself will try to lift the jar lid up, back to its normal position because outside the jar is a low pressure.
When people talk about a vacuum, I imagine that same jar of bouncy balls, but either there are less balls in it or else the same number of balls but the jar is just bigger. Either way, outside the jar is a large collection of bouncy balls each trying to make everything around them the same pressure. They push on the vacuum trying to shrink the jar, or squash the jar lid until all the balls inside and out have the same space to move around in
Referring to things we generally care about here on Earth, “vacuum” means an absence of air (or, realistically, very low air pressure). Things that are “vacuum-sealed” have the air pumped out as part of the process. A “vacuum cleaner” forces air out of an internal space, pulling in dust and debris when the outside air rushes to fill it.
There is a second definition of vacuum that you may see that comes from physics. This is referring to the background energy of space itself. A truly empty region of space still has a positive, non-zero energy associated with it – we don’t entirely know why, we just know that it does. This energy is sometimes called “vacuum energy,” “the vacuum,” or “zero-point energy,” and it has important implications in physics and cosmology. If you’re interested in further reading, there is actually a major unsolved problem in physics related to this called the “vacuum catastrophe.”
To make things even more confusing, “vacuum of space” has been used in reference to both definitions.
Yes, the vacuum in space and the vacuum sealed stuff is low air pressure. You can call it micro-pressure if you like.
There is vacuum in physics, basically in the context of quantum mechanics. The vacuum has properties that can actually get modified.
I think of vacuum and pressure as a spectrum, sort of like temperature (I’ll get there give me a second). If high pressure is a lot of gas molecules in specific volume, then vacuum is zero molecules in a specific volume. Getting a true vacuum (ie, no gas at all) is actually surprisingly difficult. But I digress.
Pressure and temperature both have a zero point – absolute zero for temp, hard vacuum for pressure. As the temperature or pressure increase, there is basically no limit on the top end of the scale.
The difference between pressure and vacuum on earth is defined relative to atmospheric pressure. In fact, there’s different pressure scales based on this concept. Ambient pressure is 0 PSIG (gauge) or 14.7PSIA (absolute) vacuum can be 0 to -14.7PSIG, pressure is any positive value of PSIG. Defined relative to absolute pressure, vacuum is 0-14.7PSIA, pressure is anything greater than 14.7PSIA. The reference is atmospheric pressure – useful on earth, less useful elsewhere in the solar system.
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