Convertible Aerodynamics at 1000fps - The Slow Mo Guys

The Slow Mo Guys: Convertible Aerodynamics at 1000fps - The Slow Mo Guys

Gav and Dan take the BMW 2 Series Convertible for a spin showing off some sweet air and liquid dynamics at over 100MPH. http://www.bmw.com/2SeriesConvertible

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Comments (18)

  • Kitzrx84 FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    I love driving thru a rain spot in a convertible; great video guys.

  • RachelFoss FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    Maximum beans :)


  • EdgarTheNoun

    1 year ago

    Nice

  • TVanderValk FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    Shout out to the NJ license plate!

  • Mtspro FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    @tanukivilla The air that's passing over the top of the windshield is what prevents the rain from hitting the driver. While the air may not be "moving" the car does displace the air as it moves through it. As the air moves up over the car, it pushes the water out of the way, thus preventing the driver from getting wet.

    An easy way to test this would be to turn on the faucet of a sink (not all the way, but just enough to have a steady stream that's falling at normal speed), blow into the water stream, and place a finger underneath where you're blowing. As you're blowing into the water, that air pushes the water out of the way. thus keeping your finger dry. Same principle applies to a speeding convertible in the rain.

  • GuruMissar FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    WHAT IF U USED DYE TO COLOUR THE WATER FIRST??
    would it be more visible?

  • tanukivilla FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    @thierer78 I appreciate the response and thank you for explaining your reasoning.

    However, I disagree with your first answer. I'm not a physicist either, but here is my thoughts on the matter. In a 3D volume there would always be a raindrop at every X and Z axis that has a Y axis (height) of the car's windshield. Maybe not realistically, but in a theoretical model it would.

    What I mean is that imagine that for every raindrop that is hitting the top of the windshield at a particular moment, there is one right behind it at the exact same height missing the windshield and trying to get the car wet. In other words, these were the raindrops just slightly higher than the windshield a moment ago, but are now level with it during this moment and are on course to hit the car. That is, unless the car is moving at a speed where it'd take the raindrop more time to fall from the top of the car's windshield to the car's interior than it would for the car to move "out of range" of that raindrop.

    At least that's how I was picturing it, which is why I'm pretty sure the answer to my third question is the car must be moving faster than gravity accelerates a raindrop from the height of the windshield to the height of the interior.

    Also, most roads curve, turn, ascend, descend, or have banks, meaning that the axis of the car's windshield would change as it traveled along the road. These tiny changes to the axis would cause "gaps" where rain drops could sneak through and fall on the interior.

    For example, let's say you have an umbrella and are running around in the rain. If you run only in a straight line it's easy to keep your entire body underneath the umbrella. However, if you try running in a circle, the edges of your body will escape from the safety of the umbrella and get wet. The same would be true of a car going around a turn where the back and some of the far side would become exposed to the rain.

    Finally, I agree with your second answer, but I think the angle/direction of the wind would matter as well. If it were blowing perpendicular to the direction the car was traveling, the windshield probably wouldn't do much.

    Again, I could be wrong about all of this, so if someone has a better answer, please share it. Thank you very much for replying and I enjoyed reading your responses to my questions.

  • thierer78 FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    @tanukivilla Those are some great questions! Your questions isolate on 3 variables involved in this "experiment": quantity of rain, wind, and speed of the car. I am not a physicist but I have come up with a few answers that may help.

    1) (quantity of rain) No. Assuming that the other variables are constant (ie no wind and that the car is going fast) this will extend across larger distances so the effect will work in a 3D environment and is not restricted to sheets of rain (you can think of a 3D environment as a bunch of sheets placed after one another).

    2) (wind) Probably. It depends on the wind speed and direction but in order for it to have a noticeable difference the wind speed would have to be pretty high (how fast the wind would have to be blowing to make a difference depends how fast the car is going).

    3) (speed of car) Yes and yes. Obviously if you were stopped at a red light (or for any reason) it would be the same as standing in the rain and you would get wet. That being said, since in the video Dan was going fast enough that he didn't get wet mathematics tells us that there must be a speed between 0 and 110 where you would no longer get wet.

    There are 2 factors affecting the way the rain reacts. The first is the windshield 'blocking' the rain and the second is the aerodynamics of the car. Firstly, you can think of the moving car as staying still and the rain as falling down and towards the car at an angle. The faster the car is moving, the closer to horizontal the rain will be moving. For the passengers to stay dry the car has to be moving fast enough for the angle to reach from the top of the windshield to the back of the rear headrests. Secondly, as the car moves forward it creates a vacuum behind it forcing for air (and rain) to be pulled in towards the area where the car just left. The car is designed to try and reduce this effect.

  • OpakaPlakebo

    1 year ago

    Who closes their eyes while driving!!!

  • UltraZero FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold OmniGeek

    1 year ago

    OMG Dan's face in the first run through the 'rain" jajajajaja.

    In case anyone is wondering, it's the force of the air that the car is pushing forward that bursts the drops before they actually hit the car itself and mist over the car.
    Seriously, Gavin really has a way of looking smart on SMG, it's like he saves it up or something, heh.

    @tanukivilla yes, possibly (largely depending on the direction and wind strength, and yes

  • EmLlewellyn FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold Short Stuff

    1 year ago

    Anyone else have a heart attack watching Gavin try and keep hold of the phantom while being in an open top car going over a 100 mph? Because I just had to be rushed to the hospital because of the palpitations it caused me.

  • 008Zulu

    1 year ago

    You guys to play with all the best toys.

  • Gamerazilla FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    And to believe I saw a couple AH videos today where Gavin was an idiot and then saw him showing some brains during a Slo Mo video. Does Gavin's brain work best with a Phantom Camera in his hands? I wonder what the LPs would be like without Gavin messing up so much... Gavin, you keep being you.

  • MykOfYouTube

    1 year ago

    Awesome!

  • Courteney516 FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    Love these guys! These videos are really cool.. except for the puke one. lol

  • TDPerks

    1 year ago

    How come the corn flour slow mo video doesn't show up ? That video is fantastic

  • tanukivilla FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    Cool video!

    Some science questions for people smarter than I am on this thread:
    1. Doesn't this only work with water coming down in a single sheet rather than from a 3D volume like a cloud covering a road?

    2. Would this still work if there was wind affecting the rain and if the rain were to come down at an angle?

    3. Isn't this completely ineffective the minute you stop at a red light or stop sign? More importantly, is there a minimal speed you need to be driving to get this effect? I'd imagine that if they drove at 5-10 MPH rather than 100 MPH this wouldn't happen at all

    Thanks!

  • Snorri FIRST Member Star(s) Indication of membership status - One star is a FIRST member, two stars is Double Gold

    1 year ago

    That was really awesome. You can see the raindrops getting smashed even before they hit the windshield