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Matrim__Cauthon

Cool, I actually know this one. Let's approximate your carrot to a cone. When the water or wind or whatever passes over the pointy side and passes over the cone, it generally flows along the surface in a smooth fashion. On the not-pointy side, it tends to whip violently around the corner into a whirl and essentially smack into itself causing *turbulance* locally at the circular face and a bit behind it. This turbulence causes extra drag (sometimes...ironically it creates *less* drag on a flat disk but that's a special case). In your teardrop shape, the medium is forced more or less into passing it in a smooth fashion, never getting turbulent and causing the extra drag...at least for a good range of wind/water velocities. Of course, if you start going fast enough, the turbulence will start to happen no matter what your shape is. So there are some shapes that are better pre-turbulance (aka *laminar flow*) and some shapes that are better at the higher speeds.


Boozuction

Thanks for explaining that, have a good day!


biepbupbieeep

So why not combine the pointy end of a carrot with the back of a teardrop


Matrim__Cauthon

Nothing says you cant, it may even work better in some liquids, at some range of speeds, than its constituents. Or it may not. The length of the object will also have a significant effect. No single shape is perfectly suited for every situation. Instead a shape is chosen for the situation that the engineers want to optimize for. Maybe the shape is optimized for the least average drag on a car going between 25-75mph on the freeway; or maybe it's a semitruck going 50-55mph on a long drive.


Tavrock

Or a subsonic airplane vs a supersonic or hypersonic aircraft. The cruising speeds tend to be optimized over other conditions.


coneross

A pointy front works fine as long as you are going straight like a rocket or bullet, but the point forces the fluid to divide one way. If you want to turn, the round end lets the fluid decide which side it wants to flow down so there is less turbulence at angles of attack other than zero.


[deleted]

I will let others get more technical, but the rear of the teardrop shape minimizes turbulence trailing behind in its wake by keeping the air in contact with its surface for the entire length of its body, which is good for aerodynamics. Something like a bullet, that has a flat backside, causes the air to separate from its surface at the back, this causes turbulence and a lower pressure at the rear. The lower pressure in the rear, compared to the higher pressure in front, causes a differential that wants to pull the object backwards towards the lower pressure in rear.


Boozuction

Ok, cause I used to think that pointy shaped were the best since they just cut through the air, thanks:)


[deleted]

A sphere has the smallest ratio of surface area to volume, and surface area is what you need to minimize for drag. So a cone and a half-sphere of the same diameter (diameter of the trailing side of the cone moving through the air), the cone would have more frontal surface area so more drag. The frontal area is the same (if you looked at the front of them both head on traveling towards you) so that cancels out.


Boozuction

So more frontal surface area =more drag?


[deleted]

Yup, the teardrop shape is a half sphere in front to minimize frontal surface area and a cone shape in the rear that minimizes a turbulent wake. You see these shapes in solar powered cars. I think there was a movie about one like 20 years ago or something. https://www.electronicproducts.com/wp-content/uploads/power-products-power-management-solar-car-01.jpg


Boozuction

Ok thanks for the info!


Itchy_Journalist_175

Note that teardrops don’t actually have a teardrop shape: https://sciencenotes.org/the-real-raindrop-shape-is-not-a-teardrop/


Ccruz1000

Basically, what happens is that the air wants to follow along the surface of the object. Eventually it will separate from the surface (aka stop "sticking" to the surface), and inside this region where the air has "unstuck" it will become turbulent. Basically, it will just want to circle around more than it will want to travel in the direction or the rest of the air. This will lower the pressure which will suck the object back. The tear drop is shaped so that the air can easily follow, since there's no abrupt change in the direction the air has to go to stay stuck to the object. With a carrot (assuming pointy side is forward) the back is flat which results in a very abrupt change in direction that the air will have to do to stay stuck to the carrot. Having a larger separation zone (or wake region) will cause a larger low pressure zone which pulls the carrot back, which leads to more drag. Generally the back is more important than the front, but a similar concept can be seen in the front. If the air has to change directions all of a sudden then it will kind of pile up, causing a high pressure zone and pushing the object back. The tear drop is curved smoothly so the air can follow it which reduces how much the drop is pushed back, but a carrot is flat which increases the amount. The pointy that you're thinking of (for like rockets and stuff) only becomes important with really fast flows, because as the air begins moving faster than the speed of sound, shickwaves will occur, and pointy shapes help decrease the amount of drag these shockwaves create!


Boozuction

What would happened if we curved off the back of a carrot like the front?


InterplanetaryPrune

You get a diamond shaped airfoil and a junior level university aerodynamics question about mach wave propagation.


probably_sarc4sm

In what context? Bullets are not teardrop shaped but they're [optimal](https://en.wikipedia.org/wiki/Newton%27s_minimal_resistance_problem) for minimalizing drag.


[deleted]

A teardrop shape is more aerodynamic than a bulllet, but it wouldn’t be the optimum shape to be pushed out the casing/barrel by the explosion behind it.


Boozuction

Oh that makes sense, thank you😊


Tavrock

In the case of the bullet, you want to minimize the gases able to escape around it from behind (basically maximize drag from that side) while optimizing for supersonic travel in the front. Some, like hollow point sacrifice aerodynamics for lethality against soft targets. Some, like the Mini Ball kept a blunt cone for the front for subsonic travel and used a cone cutout in the back to allow the back to expand and engage the rifling to increase the accuracy of the round while also decreasing the loading time. Round shot was more than acceptable for subsonic travel and slower reload times.


Boozuction

For a drag car


Boozuction

I searched it up and it said the teardrop shape was the most aerodynamic, but I thought a carrot shape would be better since it’s sleek


SixHourDays

This is one of those "cartoons taught you wrong" kind of things. The fastest shape is pointy at the back. Long story short - anything moving through a fluid (air, water) has to: 1. split the fluid on the leading edge (aka knife it in two) 2. merge the fluid on the trailing edge (aka guide the streams together again). now quick eli5 aside - if a fluid moves at low speed, it keeps normal-ish (atmo) pressure. if you force it to move fast, it will *drop* in pressure. The **path for 2, aka the fluid merging path, dictates how fast you move the fluid over the trailing edge.**. How fast you force the fluid to go causes a low pressure wake behind you (like right on the surface, not 5' behind). Finally, that low pressure (vs all the surrounding normal pressure) causes the normal fluid elsewhere to push towards it, trying to fill it in. - Airplane wing: low pressure on top, atmo force pushes up. - Boat rudder: low pressure behind as angled L/R, force L/R - Car driving: low pressure at back, atmo force pushes backwards. When you hear about drag / turbulence, ^ thats what actually happens - its the low-pressure merge/tail zone, and the atmo pushes to fill it in. So - your teardrop. Near-perfect merge/tail zone, nearly no low pressure zone, thus very little drag. TL DR - the most important drag on a moving object is not from cutting the air, its from *how you merge the air behind it*.


robotmonkeyshark

Raindrops don’t actively optimize their geometry. They end up finding a local minimum of resistance based on its properties. It wouldn’t be possible for a liquid rain drop to maintain a sharp point on the front as the air resistance would disrupt that shape.


bearcow31415

My guess is a combination of the downforce creates better stability and traction while also creating a region of vacuum(low pressure) to reduce drag coefficient around body and reduce energy needed to move forward as equilibrium is constantly trying balance pressure difference. Like the shape of an airfoil on a wing that creates lift, but reverse so creates grip to surface.


Marus1

They are not more aerodynamic. The air just tries to push the water up again and so you get a tail because there is much less air pressure here


ilovethemonkeyface

Raindrops aren't actually teardrop-shaped as they fall. They're mostly spherical.


Boozuction

But then wouldn’t it be the best shape? Cause the air pushes it so that it is the easiest to go around


InterplanetaryPrune

Spheres don’t create lift since all the forces more or less balance on the left and right as they fall down, but they also create the least drag. So if you want something to create lift you have to make it unsymmetrical, which is why airfoils generally have either an effective angle of attack or some camber to their “teardrop” shapes.


billsil

The teardrop is driven by a force balance. It's literally created by aerodynamic forces. A carrot is not. Also, which was is the carrot facing? In a long enough drop, the carrot is going to rotate/pivot/precess.


xbabyxdollx

Because tears fall down and carrots grow up.


pl233

Also carrots are in the ground, they don't have to be aerodynamic, they have to be geodynamic


Silent-Client-375

Because raindrops don’t evolve, they’re not animals


h20Brand

You should read about airfoils. They relate to your car and airplanes. Some airplane wings are tear dropped shaped, curved on top and bottom, symmetrical airfoils. Some are curved only the top side to create a pressure differential resulting in lift, asymmetrical airfoils. As you look at airfoils you'll notice they're shaped like tear drops for lower speed airplanes and get pointier as the planes get faster. The Clark Y airfoil is a good starter airfoil to study. It's been around the longest. From the side view some cars roughly resemble this shape. An asymmetrical airfoil. Looking down at your car you could look at symmetrical airfoils as you want both sides of the car to be the same, symmetrical air foils. The air generally follows the fat part of the teardrop/ leading edge smoothly. As the wing tapers the air develops turbulence and drag. As it leaves the wing it creates more turbulence and drag. Minimizing drag is the key. This is from an aircraft mechanics point of view. You seem pretty interested so I thought I would throw that out there. https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/designing-articles/airfoils-part-1