Hey smart people! A couple days ago I was watching a local news anchor report on wind speeds blowing around 50mph (80 km/h) in my state. While reporting, the news anchor was able to stand outside and get hit by these gusts of wind like there was no tomorrow.
**This is when I got to thinking; why is that when you get struck by a high speed wind gust, it doesn’t have the same effect of getting hit by a solid object such as a car at the same speed?**
To my knowledge, I assume getting struck by a car going 20mph, let alone 50mph would most likely kill you, yet if you were to stand in an open area and get struck by a wind gust of 20+ miles per hour you remain on your feet and alive?
Hopefully someone could satisfy my curiosity…or stupidity. Thank you!
In: Physics
Not much mass behind that speed. BUT one of reasons aircraft ejection seats do have limits of speed they can be used at is the fact that at very high speeds (think ejecting at mach 1+) hitting the airstream outside the cabin is like ejecting face first into a wall. That kjnd of wind is able to pull off your helmet without detaching the strap under your chin first…because it dislocates / tears your jaw off in the process.
Its all about how much mass is there coming at you at speed.
* mass — air weighs less, there is just less stuff pushing on you, it is the difference between being tackled by a linebacker or a toddler, even if they were going the same speed
* rigidity — the bits on of the car in the back push on the bits in the front, so you are receiving most all of the energy from every part of the car…air is elastic, it will stretch and compress and bits will move around you, dissipating much of the energy
Air has very little mass, and so can’t actually impart much energy to you.
It’s also very compressible and fluid, making it even more difficult to transfer energy instead of just flowing around.
You can actually stay standing in pretty ferocious winds, it won’t take you to the ground until you’re above 100mph winds.
Strapped to a chair, you can take 400+mph (this was tested in the early days of jet aircraft) without significant injury – although it’s unpleasant.
A lot of it is the mass. Take a car that weighs 1000 kg. Now take that car-shaped area’s worth of air, how much does that weigh? 1.3 kg per cubic meter. So if a car is 10 M^3, that amount of air is 13 kg.
So 13 kg hitting you vs. 1000 kg hitting you.
Also because air is a fluid, it can hit your entire surface evenly. Similar to the concept that laying on a nail will have the nail pierce right through you, but laying on a bed of nails distributes the pressure over your whole body and won’t pierce you.
Newton’s second law of motion. The force with which an object hits you is the (multiplicative) product of the object’s acceleration *and its mass*. The portion of the wind that makes contact with your body weighs very, very little compared to any solid object.
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Mass is why.
A car has a large amount of mass behind, so even at low speeds, it can impart a large amount of energy.
Wind is just moving air, there’s almost no mass to it in comparison to the car, so even at high speeds there’s minimal energy transfer to you.
Because momentum is the product of mass multiplied by the speed of the object, since a car has a lot of mass the speed doesn’t have to be very high to have a large amount of momentum. But a molecule of air has almost no mass so the speed would have to be so astronomically high to have any momentum, and its just not possible to get winds fast enough to do any real damage to a human
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