Opening a car door at a high speed

In summary, if a car door is opened while it is driving on a highway, it will increase drag and slow the vehicle down.
  • #1
Tech2025
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What would happen if a car is driving down a highway at 80Mph and one of the doors is fully opened. Will it make a big change and make it slow down or start turning?
 
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  • #2
It will increase drag, it has the possibility to turn the vehicle. It has the possibility to slow the vehicle down But not much in either case.

To many unknown variables for an exact answer.
 
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  • #3
That's a good question. I guess it would depend on what the contact with the road was like. If there wasn't good traction, I'd expect the car to turn but it could depend on something subtle like the air flow over and under the door. I think there would be a big risk of the door causing lift and tipping the car over (a third possibility).
Looks like a good project for Mythbusters. :smile:
 
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  • #4
Slow down yes. Even opening a window creates more drag.

Turning, I'm not sure. It depends on many factors.
 
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  • #5
sophiecentaur said:
I think there would be a big risk of the door causing lift and tipping the car over (a third possibility).

There is no risk at all for that, none. If magically that was possible, a person could not have the strength to hold the door open with that much force.A door open will not cause lift, and doors have different shapes that will have different effects.

80 is not high speed, and not fast enough to overcome the weight of the vehicle. You would have to attach a small airplane wing to a car and then use it as a flap is used to cause lift.
 
  • #6
anorlunda said:
Slow down yes.

Depends.

If cruise control is on, the car will not slow down.
 
  • #7
Tech2025 said:
What would happen if a car is driving down a highway at 80Mph and one of the doors is fully opened. Will it make a big change and make it slow down or start turning?
What I'd like to know is how are you going to GET it open and how will you KEEP it open? 80Mph wind against a car door is going to be a LOT of force. I doubt one person could do it, particularly given the odd angle at which you'd have to exert the force. If you tried to walk in an 80mph wind, holding a car door directly against the wind, I'm sure you could not stay upright.
 
  • #8
phinds said:
What I'd like to know is how are you going to GET it open and how will you KEEP it open? 80Mph wind against a car door is going to be a LOT of force. I doubt one person could do it, particularly given the odd angle at which you'd have to exert the force. If you tried to walk in an 80mph wind, holding a car door directly against the wind, I'm sure you could not stay upright.

Actually, having just spend a week in the Scottish mountains, I can say that it's difficult enough to walk against a 60mph wind without the handicap of a car door.
 
  • #9
Tech2025 said:
What would happen if a car is driving down a highway at 80Mph and one of the doors is fully opened

Assuming the door was mechanically opened fully, a slight pull on the steering wheel to correct its path would be felt, with a slight increase in throttle to maintain speed.
 
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  • #10
phinds said:
What I'd like to know is how are you going to GET it open and how will you KEEP it open?
There is a lot of special effects expertise that could be brought in here.When they want to slip a car into a roll, they fit a ram underneath which lifts the side of the car up. The same sort of force would be needed and I'm sure it would be simple bread and butter stuff. But you are right; an arm and shoulder wouldn't do the job.
Outhouse said:
A door open will not cause lift, and doors have different shapes that will have different effects.
I bow to your superior knowledge there.
 
  • #11
Yes, the door would theoretically be held open mechanically.
 
  • #12
Time for a calculation. The front doors on my truck have roughly 10 square feet of area, and open about 50 degrees. The projected area of one door fully open is 10 ft^2 X sin(50 deg) = 7.7 ft^2. Assuming Cd = 1, then the drag force = 0.5 X rho X V^2 X area = 0.5 X 0.075 lb/ft^3 / 32.2 ft/sec^2 X 117^2 ft^2/sec^2 X 7.7 ft^2 = 120 lbs force. Double that for both doors fully open.

The power to overcome that drag is 120 lbs X 117 ft/sec / 550 ft-lbs/sec/hp = 26 hp.
 
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  • #13
It would definitely increase drag, so would slow the car unless the driver puts their foot down.
It could also produce a turning momentum which might not do much on a normal road but would be disastrous if the road had ice on it,
 
  • #14
Not a door on a car, but the Falcon F16 with air brakes being looked at.
The mechanic is opening them by hand in the video for a check post or pre flight.
Same principle as a car door - induced drag for landing, or in flight maneuvers.
At around 150 knots about 1200 pounds extra drag, with the force depending upon speed of the aircraft.
So, in principle, the car door question does have a real life application!
 
  • #15
_Any_ assymetry to the drag force on a car would in theory require some steering input to correct. It's a question of degree.
 
  • #16
CWatters said:
_Any_ assymetry to the drag force on a car would in theory require some steering input to correct. It's a question of degree.
Well, any yaw asymmetry anyway. Pitch asymmetry (e.g. sticking your hand up from dead center in the sun roof) would have no relevant effect.
 
  • #17
Yaw probably right? :wink:
 

What are the dangers of opening a car door at high speed?

Opening a car door at high speed can lead to serious injuries or accidents. The sudden rush of air can cause the door to swing open with great force, potentially hitting other vehicles or pedestrians. It can also cause the person opening the door to lose their balance and fall out of the car, resulting in injuries.

Can opening a car door at high speed damage the car?

Yes, opening a car door at high speed can potentially damage the car. The force of the wind can cause the door to bend or even break off its hinges. This can result in expensive repairs and may render the car unusable until it is fixed.

Is it illegal to open a car door at high speed?

In most places, it is not explicitly illegal to open a car door at high speed. However, it can be considered reckless or careless driving, which is a traffic violation. It can also be considered a contributing factor to accidents and may result in legal consequences.

What is the proper way to open a car door at high speed?

The best way to open a car door at high speed is to first slow down the car and come to a complete stop. This will reduce the force of the wind and make it easier to control the door. Then, use one hand to hold onto the door handle and the other hand to support yourself. Open the door slowly and carefully, ensuring that there are no other vehicles or pedestrians nearby.

Can opening a car door at high speed affect the air pressure inside the car?

Yes, opening a car door at high speed can cause a sudden change in air pressure inside the car. This can result in discomfort or even ear pain for the passengers, especially if they have existing ear or sinus issues. It is recommended to open the windows slightly to equalize the air pressure before opening the door at high speed.

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