An NFC is a signal, your card emits that signal which acts like a password to your bank account.

Instead, your phone can scan and copy this signal, and then emit it themselves to mimic this code and appear to be the card doing the work

Security risks, sure, but it’s way riskier using you card since that’s always emitting the signal, your phone is not

Surely you mean doubling the speed requires four times the power, not eight.

Because cars are ridiculously overpowered. As anyone who's owned an old VW can tell you, 40-50 horsepower is enough to get you anywhere you need to go at highway speeds. Old VWs are not particularly lightweight, either.

Horsepower beyond about 50 exists for entertainment purposes.

I was planning to write something like this, but you beat me to it. I really like this idea, that from the perspective of photon, there is no such thing as vacuum. Every atom along its trajectory(from the "perspective" of photon) is right next to each other.

That is what our power sources already do.

That's what a wind turbine is

Yamaha also used a cross-plane crank, so it was basically half a cross-plane V8 and they also sounded somewhat similar.

Underwing versus on the back is not the same as why one on the vertical stabilizer or just the air intake there

If you have an odd number of engines you need to place one in the center line of the airplane and with a jet engine, you can put it in the front line with propellers.

You can but even the number of engines under the wing or on the body. 4 engines on the back have them placed side by side like a Vickers VC10

3 engines existed primarily because of ETOPS rating, you could fly longer over open water with 3 compared to 2 engines and the cost will be less than if you have 4 engines. A minor part is that it adds high-altitude takeoff performance in locations like Colorado which is at 1-mile altitude.

They have disappeared because engine performance and ETOPS regulations have changed so you are allowed to do the same flight with just 2 engines and it is a cheaper way to build and operate aircraft

Boeing 727 have all 3 engine in the rear, and McDonnell Douglas MD-11 had 2 under the wings and 1 in the back. So 2 engines under the wings or on the back are unrelated to the vertical stabilizer position of a third engine.

It doesn't really make sense to ask "how much time has passed from the perspective of a photon", because we can't build something called a "reference frame" for the photon.

Whenever we talk about special relativistic time dilation we must do so by comparing the rate that time is passing in two different reference frames. If I am moving along with you, we are in the same reference frame, but if we are moving relative to each other, then we are different ones. You can think of a reference frame as being a way of describing the universe from your perspective, and when we talk about time dilation or length contraction we have to have two reference frames to compare together. Time always passes normally and distances are always the same in your own reference frame: you won't see your own clocks ticking slow or fast or your own rulers changing length, but you will see that your clocks disagree with those of someone who is moving relative to you and that you and that same person will disagree on how long your rulers are.

Time dilation and length contraction can be thought of as consequences of one basic fact about the universe: all observers, no matter how they are moving, will agree on how fast light is moving. If you're moving away from me at 100 mph and you shine a laser at me, you will measure the light leaving the laser as moving at c. I will measure the light from your laser as moving at c as well, not c-100 mph. In order to agree on how fast light is moving while we are moving relative to each other, we must disagree on how fast our clocks are ticking and how long our rulers are.

But if we were, hypothetically, to be moving relative to each other at c, we would encounter a paradox: light moving parallel to that reference frame would have to be both moving at c (as it must be in all valid reference frames) and be stationary at the same time. This is a contradiction, so we cannot construct a reference frame for the photon, and without a reference frame it doesn't really make sense to talk about time dilation or length contraction.

What we can say, however, is that as something moves arbitrarily close to c that the time it would see pass while traveling between two points would get arbitrarily close to zero and the distance between those points would as well. People often make the slight error of thinking that because the limit goes to zero here that the answer is that it is zero when v = c, but it's more precise to say that the limit approaches zero as v approaches c, but does not exist at v = c. Sort of like how 1/x gets arbitrarily large as x approaches 0 from the positive side, but 1/x does not actually exist when x = 0.

The biggest benefit that I remember from my design classes of having the engines on the tail is the reduction of adverse yaw. When you design planes, you have to design them in a way that if things break they don't crash. So planes need to be designed to be able to fly with only 1 engine. If the engines are on the wings, they are further from the center of gravity, and they'll make a bigger moment (or twisting force) on the plane. This makes it harder for the rudder to overcome, so you'll need a larger rudder and a more powerful actuator to control the rudder, which is more heavy. If the engines are on the tale this is less of an effect and you can design a smaller rudder and actuator (not exactly an apples to oranges comparison as you'll need to increase the structural parts of the tail to account for the engines). On top of this, it looks cool, which is a surprisingly big factor in aircraft design, especially for business jets. There are a few other benefits, for example less issues with tailwash from the engines wake and a few other things, but you get the gist.

It’s still hard but it’s much easier to get them back than it was the first time. Hard to gain hard to lose.

Oh yeah totally. The ol S980. Or the 981, you know, whatever it takes

Really? I thought the “Homer flipping the tractor” gag was meant to say he’s so inept he could screw something up in a really difficult way 😂

>There were a few standards

There were, but the only ones that I remember were "Soundblaster" "Soundblaster 16" and "Soundblaster 32" that were only standards because those cards were very popular so most games would support them. So competitors made their cards compatible with that interface.

Every model has limits. The point of the balloon model here is to explain how a cosmologic event horizon can occur.

I agree with you that it's limited as a way to visualize the general idea of the expansion of the universe, since it requires the same essential leap as not using a model (i.e. that the universe isn't expanding into/through anything).

This sounds like a reasonable ELI5 explanation, why not put that as the top level comment?

Legend has it that every time you reply, an angel loses a brain cell.

Unfortunately, imagining "nothing" beyond the balloon is where everyone gets lost. Most people, with sense, would easily counter-explain that the balloon could not expand without the "room" to be able to expand. I mean, sure the "thing" expanding also made/caused the actual phenomenon of expansion, but we'll let the philosophers continue haggling over that paradox.

> Why do some cars have an engine in the front and others in the back?

Mass distribution and the torque that can be generated on a driveshaft depending on whether the drive wheels are at the same end as the engine or the opposite end. Mass distribution affects stability and control, just like it does with a plane, like I said.

Yes, all of airplane design can't be explained in a reddit comment. Center of gravity, lift, and the tail force to control the plane are the reasons for choosing the engine location on a plane. Otherwise an unbalanced plane is difficult and dangerous to fly, with unstable recovery modes. The center of gravity, center of lift, and the forces applied by the control surfaces have to be balanced to fly the plane with stability. Large, heavy engines are usually placed near the center of mass of the plane. Engines placed elsewhere have to be balanced in other ways to keep the whole plane level and well controlled.

Yeah, exactly, you're just listing stuff, you're not even trying to actually say which ones matter for what.

Why do some cars have an engine in the front and others in the back? Why do some planes have straight wings and some swept? Why are missiles pointy but torpedoes round?

bEcAuSe ReAsOnS LOL

Yes and speed translation comes down to the difference between the original answer of what's more important for each piece of equipment,. Horsepower or torque? For farm equipment it's torque, for cars horsepower. If it's heavy and you need torque for moving heavy loads slowly but with power. taking a hatchback up a hill and onto the freeway horsepower, there have been some awesome answers so far in the responses that nailed it. This was a great question to ask and I hope a lot of others got their answers as well!

Big planes have multiple big engines. It makes sense to mount big engines on the wings, because that's where you have lots of physical space for them, and that's where the lift is generated, so they're lifted by the wing directly. Trying to mount them to the fuselage would require heavy support structures to mount the heavy engines, increasing overall weight beyond the engines themselves, putting more stress on the connection between the wings and the fuselage. It also makes the maintenance much easier, because the engines are close to the ground, rather than high up. The downside is having engines close to the cabin. This is true both for jet and old piston engines.

A small plane has smaller engines, but also very little ground clearance. So it's pretty impractical to try to put them under the wing, and it'd complicate maintenance to put them inside the wing. At the same time, because of the size difference as compared to the airliner, mounting them on the body doesn't require as much reinforcing, so you don't suffer the same weight penalties. It has an added bonus of making the cabin quieter, which for a luxury jet is certainly a factor.

> Well... Why? What design requirements dictate the specific design choices?

Similar ones. For a car, engine, and tire size: power, fuel consumption, grip, suspension, stability, cornering, ride comfort, cost.

I already listed some flight requirements that dictate design choices for a plane:

> amount and location of weight, payload, thrust, control, and other flight characteristics

Absolute masterpiece of verbal evisceration

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That's outside the scope of the question asked by the OP. They asked about wing mounted and vertical stabilizer mounted engines.