Winches

[PhysAssist]

No, it would weigh (mass) the same, because there's still the same number of molecules. No mass is gained when it cools. The force pressing in from the outside would appear to increase, but in reality it's constant, it's just that there is not the same force pushing back from the inside, because the molecules contract as they cool. If it was in a medium that didn't expand and contract as much as air, (or steam) you wouldn't get effects as dramatic as this:

The reason we know the force one experiences with a vacuum is caused by the weight of the air, is because absolute vacuum is the weight of the air (about -14.7 psi). If you were on top of Mt. Everest and sucked all the air out of that glass, or this barrel, the vacuum would be less, (correction: not less, but the force the glass experiences would be less) because the atmosphere would only exert about 4.9 psi on the outside instead of 14.7psi. (if it was at sea level).

Naw, absolute vacuum is absolute, however, it is actually a theoretical concept because even the hard vacuum around deep space has some ambient pressure- just not enough for us to survive or appreciate.

BTW, while you have some points re: the weight of atmosphere, and it is certainly why the can crushed, IDT that your analogy for the empty glass works.

I think it only works if the glass is upside down in a saucer of water when as the pressure inside is reduced, water gets "sucked" [actually pushed by atmospheric pressure] UP into the glass.

I do think that the suction of the mud is more surface tension, otherwise what creates the vacuum that reduces the pressure and cause atmo pressure to hold it down?

Respectfully,
Thomas

 

[PhysAssist]

No, it would weigh (mass) the same, because there's still the same number of molecules. No mass is gained when it cools. The force pressing in from the outside would appear to increase, but in reality it's constant, it's just that there is not the same force pushing back from the inside, because the molecules contract as they cool. If it was in a medium that didn't expand and contract as much as air, (or steam) you wouldn't get effects as dramatic as this:

The reason we know the force one experiences with a vacuum is caused by the weight of the air, is because absolute vacuum is the weight of the air (about -14.7 psi). If you were on top of Mt. Everest and sucked all the air out of that glass, or this barrel, the vacuum would be less, (correction: not less, but the force the glass experiences would be less) because the atmosphere would only exert about 4.9 psi on the outside instead of 14.7psi. (if it was at sea level).

BTW, did you see the mythbuster's tank car crush?

 

[GPintheMitten]

Interesting discussion about vacuum. But it is the water molecules bond due to shared electrons between molecules (covalent bond) that make it extremely difficult to brake free in deep wet mud.

 

[CobyRupert]

Interesting discussion about vacuum. But it is the water molecules bond due to shared electrons between molecules (covalent bond) that make it extremely difficult to brake free in deep wet mud.

ok, ok... I'll buy that...I guess...
So when I step in 12" of mud and it pulls my boot off, then I put my foot back in, and I finally manage to pull the boot, and it comes out with a sucking sound, I agree that there is cohesion, hydrogen bonds, friction between the boot and mud, etc.. but that sucking sound tells me there's a vacuum being created in the space under the boot when I pull it out. Isn't this the same when you try to pull the body of a sunk vehicle out of the mud? Army friends have told be they use explosive to break these bonds and/or vacuum when flat bottom tanks get mired.

Speaking of vacuums: Here's any interesting thought experiment.
We all remember Star Trek teleporters that could beam down Captain Kirk and Spock to a planet from the ship, the stuff of science fiction right? Isn't creating a vacuum a sort of tele-portation? Follow, if you will: Think of the earth and 100,000 miles of space around it. There's a finite amount of air, and a finite amount of space. When we create a vacuum in a 55 gallon drum here on earth, we're actually pushing a barrel size quantity of atmosphere farther out into space, and thus (all things being equal in our 100,000 mile model), haven't we've teleported a barrel size portion of "space" into the barrel?

 

[ovrszd]

Sorry for any appearance of hi-jacking this thread. I love these discussions. I always learn something. It's usually way over my head. The 3 technical experts in this discussion are trying real hard to keep it down to a level that I might understand. And I appreciate that!!!

 

[bcp]

It isn't exactly the "weight" of the air, but the pressure difference. The same experiments done in weightless conditions in the space lab would do the same thing.

Bruce

 

[sdef]

I have a 9k# winch on front of my Jeep GC in a custom bumper and seldom use it. But when I need it- I need it. It has been used for things like supporting an old shed upright so it could be repaired to recently winching a friend's Ford tractor out of the mud at the bottom of a long hillside where it had been stuck for a couple weeks and it took all of the single line pull the winch could muster. Also have a 12k# winch that used to be on the back of my tractor and used to pull trees leaning in the wrong direction that I was cutting down to clear the property for my new home, now residing on the front bumper of my 2015 Dodge 2500 Diesel (barely adequate size winch).

Years ago I started out using a 2" receiver mounted, portable unit on the front or rear, but there are major limitations to that setup, especially if needed often and the mounted vehicle is mired.

+1 on the Anderson type connectors as I have them on all of my vehicle batteries, 1 gauge and 2 gauge battery jumper cables, winches, inverters, etc.

If another vehicle is available to tug one out of the mess, a snatch rope can be a quicker and easier method. A snatch strap is a less expensive, less effective option.

Here is what I also carry in each vehicle (unused so far), along with 30' snatch strap, 26.4k# bridle, synthetic or wire rope winch cable extensions, 6.5T and 8.5T steel bow shackles, etc., etc.:

- Truck: 1 1/4 Inch High Strength Synthetic Kinetic Recovery Rope | ASR Offroad

- Jeep: 7/8 Inch Synthetic Recovery Vehicle Recovery Rope | ASR Offroad