And I am stopped, I notice that I am pulled towards the vehicle. I would have thought I'd be pushed away
when I'm stopped at a light to turn for example, and someone going straight goes by, my car rocks a little. The faster they go the more I rock. But the car moves towards the passing vehicle.
what is happening?
Usually you get an initial push from the bow wake coming off the front of the car. Then you get sucked into the vacuum at the back of the car as air rushes in to fill the hole.
The bigger the vehicle and the faster the vehicle the more noticeable it is.
That's what I expect but it isn't what happens. I feel my car get pulled towards the approaching car as it passes
Sounds like a venturi effect. The bow wave of the passing car is forced into a smaller area (constricted) by your car, which makes it speed up and drops the pressure. It's the interaction of the two cars that matters.
I suspect Toyman might be thinking of small boats, because he is known to mess with them. In that case, the stopped boat is able to move sideways significantly and doesn't restrict the water. In other words, it acts more like a point on the water than a fixed object. A car won't move sideways much at all, just a small rocking on the springs, so it'll be a different effect. I don't spend enough time in boats these days, when you try to pass close to a wall does it pull you in?
In reply to Keith Tanner :
Yes. A boat will get sucked into a bank or wall due to the venturi effect. It has to be a long wall or a fairly steep bank. You will also notice it when traveling parallel to another boat. There is some discussion that that contributed to the Evergreen ship getting stuck in the Suez Canal.
If you want a slow motion version of air coming off a vehicle, get passed by a tractor trailer rig while driving a large RV. The high pressure air coming off the front of the truck initially pushes on the back of the RV making it turn toward the truck. As he comes up beside you that high pressure air pushes the RV toward the emergency lane. Once your front bumper is even with the truck it it fairly neutral with some pull towards the truck, probably due to the venturi effect. As he completes the pass the low pressure area at the back of the truck pulls the RV toward the truck.
Interestingly enough, I never noticed this when pulling my enclosed trailer. Probably due to more tires on the ground and better stability.
Would a moving car passing a stopped car be alongside each other long enough to create a venturi effect?
It would be interesting to sit beside the road with a pressure gauge on either side of a parked car and take some measurements.
Pretty far off topic, but has anyone noticed how much a stationary car rocks when the windshield wipers are on high? Pretty surprising (to me, anyway).
wheelsmithy (Joe-with-an-L) said:Pretty far off topic, but has anyone noticed how much a stationary car rocks when the windshield wipers are on high? Pretty surprising (to me, anyway).
If they're timed up with the natural frequency of the suspension, and the dampers are blown, they could rock the car over!
Robbie (Forum Supporter) said:wheelsmithy (Joe-with-an-L) said:Pretty far off topic, but has anyone noticed how much a stationary car rocks when the windshield wipers are on high? Pretty surprising (to me, anyway).
If they're timed up with the natural frequency of the suspension, and the dampers are blown, they could rock the car over!
Welp, I know what I'm doing this weekend.
A couple times when I was on a beach on the Columbia river downstream from Portland Oregon and a loaded RoRo approached (Mazda and Toyota off load vehicles in Portland) the water level started rising when the ship was 50 yards away and eventually rose along the shore up to 2-4 feet as the ship approached with another 2 feet or so of wake waves on top of that, which is pretty impressive to watch happen as it allota water moving and it seemed magical- "the ship was too far away- how is this happening?". That 4-5 feet of surge pushed the the river 15'-20'up the steep part of the bank sending families scurrying and picnics floating. The really amazing part was as the ship was passing the river started to suck out off of the bank eventually emptying down onto a large summer flow level flat which left 20-30 yards of river bottom exposed, then it all rushed back in sloshing around for awhile It really brought the notion of a ships 'displacement' into focus, the amount of stored energy at play, and was an impressive visual display of fluid dynamics re a body in motion.
Side drafting is a thing.
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