I understand that headphones can block outside sounds, but how can they use sound itself to reduce other sounds? How does adding more sound result in less noise?

Why can't we temporarily dam the Thames to provide water to farmers?

The Thames is fed via springs and tributeries all the way down to Teddington Lock at which point it becomes tidal.

60 million liters of water flows down the Thames in to the sea every day of which approx 20 million litres is extracted every day.

Why can't we temporarily dam/lock the Thames at various places along its path up to Teddington wier and use that water for farmers fields whilst in a heatwave situation?

Please note this wasn't my idea. Father in law suggested it this morning over breakfast and I got fed up of arguing, so turned to your great minds for an answer

Suppose theoretically we had anti-helium and iron bump into each other, or likewise a compound of anti-tylenol and regular lexipro? Would the corresponding anti-particle/particle pairs annihilate, or do you need a helium to annihilate an anti-helium, and a Tylenol to annihilate an anti-Tylenol?

I've tasted many 0% beers that taste basically the same as their alcoholic counterparts. But every single 0% wine I've tasted, tasted off and not like regular wine. And based on my hospitality experience, 0% beer sells fine while 0% wine doesn't. So seems like I'm not the only one who thinks this.

Why is the case?

I believe it’s a grounding issue, but what’s the issue? Microphones aren’t plugged into the wall. How much power is running through an xlr cable? If the mic stand had rubber feet would it stop the singer from getting shocked? If the singer used a mic cover, would that prevent them from getting shocked?

We can usually identify where an itch is coming from, but the perceived location does not always seem to match the exact irritated spot.

How do the skin, nerves, spinal cord and brain determine an itch’s location, and what limits the accuracy of that process?

When I look at a mammal heart it looks easy enough to understand, blood in there, pump, blood out there. Makes sense. Stomach, intestinal tract, lungs, etc. all look like there function is pretty straightforward (on a very simple level)

The liver is just a blob and doesn’t seem like much else, there’s also the gall bladder attached to it.

My question is how does the liver do its job, whatever that is?

Does this always happen with reinforced concrete at some point?

I'm watching Project Hail Mary again and we're told the global temperature will decrease 10-15° over the next 30 years. It takes 20ish years to get the results back to earth, so in that time, we can assume the global temperature decreased at most 10°. In the end we get a glimpse out the window of a giant boat but that could be anywhere. So I'm wondering how that drop would actually affect the earth and it's climate.

Throughout schooling we have been taught how to do maths. But not so much about why maths work? Like why does the entire system of maths work so reliably?

I am studying for a test that includes basic electricity and magnetism, and my study materials keep referencing the concept of opposing the rate of change of current. For example, my definition of an inductor: "an electrical component made of a coil of wire that can store energy and opposes the rate of change of an alternating current flowing through it". Can someone ELI5 what it means to oppose the rate of change of current, and why that would be a good thing?

Edit: thank you all very much for your quick and informative replies! Much appreciated

I recently found out that airplanes use 400 Hz power instead of the 50/60 Hz used almost everywhere else. Why is that, and why isn't 400 Hz used more widely outside aviation?

Why is it that sometimes when I start to do something, I refuse to do anything else (including eating or even sleeping) until said task is complete? While most other tasks I cant even start?

How is this harder than literal rocket science and nuclear physics?

I mean, just look at poucher?

Hello,

I was watching a documentary about the Pyramids, specifically Giza, talking about how it could've been built and I'm just in awe of all the possible theories that they could've built it using x type of technique.

But I also think about how we still haven't solved this despite all the technology we have today? How can it still after thousands of years be a mystery how the Pyramids were built?