Why does water splash back onto the hood?

PugDad

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Yes. Kind of why I asked.

Sorry, I thought this was a forum to discuss the Bronco Sport. I don't know why you care why I ask why something happened. 🙄
No need to apologize, ask away. There are those in the world who can’t see beyond their own self worth. Which in my experience never amounts to much.
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Barry S.

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Air moving over a surface has a boundary layer. The closer you get to the surface the slower the air moves. In your case, the water on the hood is in the boundary layer, which means the air moving over it is slower than your forward speed. As you brake, you observe Newton's First Law (inertia) in action: the water on the hood wants to continue moving at the same speed it was moving, and its inertia overcomes the relatively slow air movement in the boundary layer and friction of the surface of the hood. Eventually, the water will fall off the front of your hood. When it does it will drop into the slipstream of air moving around your car and out of the boundary layer. Once free of the boundary layer air into the full-speed slipstream, you see Newton's Third Law (action and reaction). While it may appear the water is being blown backward, it is, in fact, the pressure of air from the slipstream forcing the water to move up and slow down while your car continues forward.
If I was a betting person, I'd bet you're an engineer.🙄
 

Jumbo1953

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My Bronco Sport and Honda CRV does this. I believe Mark S is correct.
 

PugDad

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Air moving over a surface has a boundary layer. The closer you get to the surface the slower the air moves. In your case, the water on the hood is in the boundary layer, which means the air moving over it is slower than your forward speed. As you brake, you observe Newton's First Law (inertia) in action: the water on the hood wants to continue moving at the same speed it was moving, and its inertia overcomes the relatively slow air movement in the boundary layer and friction of the surface of the hood. Eventually, the water will fall off the front of your hood. When it does it will drop into the slipstream of air moving around your car and out of the boundary layer. Once free of the boundary layer air into the full-speed slipstream, you see Newton's Third Law (action and reaction). While it may appear the water is being blown backward, it is, in fact, the pressure of air from the slipstream forcing the water to move up and slow down while your car continues forward.
I am not sure if you dazzled me with brilliance or baffled me with bull****. I believe the former. Great response . That’s what makes these forms so educational and information gathering.
I tip my hat.
 

Mark S.

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I am not sure if you dazzled me with brilliance or baffled me with bull****. I believe the former. Great response . That’s what makes these forms so educational and information gathering.
I tip my hat.
The sign of a true master is the victim never knows for sure... :bandit:
 


Dude

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I like to play the balance the water on the hood game. 😃
To increase the level of play .. ceramic coat the hood .. the game has become much harder for keeping the water on the hood or to roll off the water at a time of your choosing (except the part of the splash back … rarely get that now).
 

Meanderthal

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Air moving over a surface has a boundary layer. The closer you get to the surface the slower the air moves. In your case, the water on the hood is in the boundary layer, which means the air moving over it is slower than your forward speed. As you brake, you observe Newton's First Law (inertia) in action: the water on the hood wants to continue moving at the same speed it was moving, and its inertia overcomes the relatively slow air movement in the boundary layer and friction of the surface of the hood. Eventually, the water will fall off the front of your hood. When it does it will drop into the slipstream of air moving around your car and out of the boundary layer. Once free of the boundary layer air into the full-speed slipstream, you see Newton's Third Law (action and reaction). While it may appear the water is being blown backward, it is, in fact, the pressure of air from the slipstream forcing the water to move up and slow down while your car continues forward.
Well all of this makes sense, except that it isn’t the air that is moving, it’s the car (and the water on the hood). There is potentially a frame of reference argument here but I don’t think it changes the end result. I suspect that since the OP was approaching a stop sign and was heavily braking, the water on the hood would continue forward and disconnect from the hood. Any momentum the water has will carry it further from the vehicle as the vehicle continues to slow (braking). Yes, once the water is airborne the friction it has with the air, especially because it spreads out and has a greater area, increases dramatically. That friction is far less than the friction slowing the vehicle, so the water would continue and fall to the ground. Once the water leaves the hood it might rise up some because the air is being forced up by the front of the vehicle but it would not be force back toward the hood, at least not at these speeds (assuming this isn’t happening at higher speeds because of the braking).

My BS has the Aeroskin II on the front of the hood so it does develop a pretty big puddle on the hood but that puddle has to exit to either the left or right. That is to say that I have not seen this happen on my BS.

I think that if Mark’s explanation was accurate, this would be a common experience on other vehicles. I haven’t driven an extensive list of other vehicles but I have driven quite a few. I haven’t ever noticed any water on the hood that goes forward when braking being thrown back up into the air and onto the hood.
 


davidb1841

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My F250 collects some water but it’s a “no worry” situation. Same for my BS. It’s not like the water is going suddenly migrate to the windshield and obscure your vision. It’s in an no air flow spot. And that’s why it accumulates. Once there is enough volume it will run off.

I think it’s more of an annoyance for you than an actual problem. Ignore it and enjoy your BS.
Same here....I also have an F250 and a BS.......same hood water too....which does not concern me.....
 

Devbloggs

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little off topic, but have you noticed, at highway speeds, when you use the windshield sprayer, a bunch gets sent onto the hood

I think the "gutter" for the wipers is to blame
 

Meanderthal

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Active Grille Shutters opening/closing is what causes the water to splash back on to the hood.
That’s an interesting theory but I would like to know what about the grille shutters opening or closing would cause this to happen.
To the OP, I don’t think there is anything to be concerned about here but it would be nice to understand what is happening.
 

BravoAlpha

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It’s a built-in meteorological instrument

water on hood = raining or has rained
no water on hood = no rain or no rain yet

The hood has many other functions and features
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