Title text:
Reductio ad absurdum fails when reality is absurd.
Transcript:
At the left, a teacher is holding a pointer, pointing at a picture on the screen.]
[The picture shows a hydraulic lift, with a small fluid vessel on the left connected to a tube at the bottom, which connects to a large vessel on the right. On top of the large vessel is a weight labeled 1000 and a Cueball. The fluid in the large vessel is labeled with an upward arrow. Megan’s hand is over the small vessel, with a downward arrow indicating that she’s pressing on it.]
[Cueball, Hairbun, and Blondie are sitting at school desks going right to left.]
Cueball: No, that can’t be right.
Cueball: If hydrostatic pressure worked that way, then you could use it to make machines that exert near-infinite force.
Cueball: And ancient people could have demolished entire mountains just by drilling small tunnels and filling them with water.
[Caption below comic:]
When I first learned about Pascal’s law, I tried to disprove it by showing that it would lead to absurd consequences, but it turns out hydraulic presses and ruina montium are both real things.
Source: https://xkcd.com/3087/
WHAT??? Why didn’t they teach me this in physics school???
They didn’t?
How do you think vehicle brakes had always worked? You think lightly pushing your foot on a pedal brings the 4,000 lb car to a stop with farts and whistles?
Well depending how close to going out your brake booster pump is, it very well could be powered by farts and whistles!
The dude is clearly underestimating my farts.
They did. You just weren’t paying attention, and it was only one day of the class. And it was one of the easy exam questions, so you didnt remember struggling on it.
it is really one of the basic physic principles that is taught in the high school, so i have no idea what kind of physic’s school would not teach that.
School of Christian Physics
They certainly should’ve; it’s just a consequence of how pressure is force divided by area.
Here’s an analogy that might make it feel less weird: you know how you can reduce the force needed to lift a heavy weight by using a lever and making the lever arm longer? This is the same kinda deal, except that instead of varying the length of the lever arm you’re varying the diameter of the hydraulic pistons.
You don’t get it for free, of course: just like how you have to push the long end of the lever a longer distance to lift the weight a shorter distance, in a hydraulic system you have to press the plunger further down the small-diameter piston to move the plunger in the large-diameter piston up a smaller amount.
(I thought of mentioning pulley systems as an analogy too, but of these three varieties of gaining mechanical advantage I find pulley systems to be the most confusing, LOL.)
A simple experiment to get an intuitive understanding of pulleys:
Take a piece of string and hold one end in your right hand, then hold your left hand higher and let the string run over it and hang down.
Now as you move your right hand up or down, the free end will move the same distance. But if you move your left hand up or down, the free end must move twice the distance, because you have string on either side of the hand that must both move that distance. So you are amplifying the movement, getting twice the movement at half the force.
If instead you wanted to amplify the force, as in a pulley, then stand on the free end of the string (so it’s no longer free) and pull down with your right hand. You are now amplifying the force exerted on your left hand, because it moves only half the distance of the right, so you get double the force. And this is exactly how a pulley works. Add more loops to get even more force at the cost of even more movement.
I figured this out while playing with the cats, and it made pulleys just make sense. Hopefully it can do the same for someone else :)
Archimedes over here with his bigass lever
Love his famous quote:
No, you’re right, pulleys are mechanical witchcraft, I tell you!
Another example: gears. You have a small wheel moving a large wheel trading speed for torque (or vice versa).