Why is strong wind able to sway and knock down a tree, but a human who weighs far less could easily wander through the same wind?
In: Physics
In addition to what people have said below, trees are also rooted to the ground, which means that when a really strong gust comes, they don’t move with it (like humans do), but instead are forced to bend and break.
Humans are lower to the ground and have less surface area while trees have leaves and branches that are high off of the ground and catch the wind.
Surface area plays a big part in this. If you’ve ever spread your arms and leant into the wind, you instantly feel the increased effects of the wind. Now imagine you become the size of a tree and you can’t reduce your surface area to get out of the wind. Suddenly there’s a whole lot of pressure on the tree and something has gotta give.
Because humans have far less surface area, and thus experience less air pressure per square inch.
I believe this has to do with both the surface area of the tree and it’s center of gravity. People present less surface to press against and their weight is closer to the ground. However, a tree presents a lot of surface and the branches catch the wind. Then having its weight higher in the air it is easier to sway and possibly topple.
I’ll try to summarize some parts others have mentioned, and add more.
First off is **Scale**. Trees are MUCH bigger than humans, so there is more surface area to catch wind, but also a taller tree create creates a larger **Moment of Force**. A moment of force is a force that creates a rotation movement: If you push a pencil on one end, it will just rotate, compared to pushing it at it’s center of mass, which moves the pencil without rotation (translation). Moment of force is equal to Force x Distance, so forces further away from the bending point create greater stresses.
Second is the **ability to bend** (there’s probably a better term for this, but I can’t think of it). If a human ends up getting hit with too much wind, they just fall over or stumble by moving their base(feet). Trees can’t do this; they either withstand the forces and stand tall, or succumb to the forces and fall. There’s no “recovery” for them.
Lastly, is important to note: **most of the time, wind doesn’t knock over trees – its the lack of wind**. If you’ve ever been in a wind storm, trees usually fall in groups, within seconds of each other. Trees get pushed to one side by string winds, but because it’s usually a (somewhat) gradual buildup of forces, trees can withstand it. But if there’s a sudden lull in the wind, **all the forces applied to the tree disappears**, and **all the tension in the tree whips it back the opposite direction** within a few seconds ([like this](https://www.youtube.com/watch?v=Lhy-jK93hY4&ab_channel=SoCalCoaster521)), and that quick switch is the killing blow for most trees.
Because of one very simple principle that you learn about in week 3 of physics 101: https://en.m.wikipedia.org/wiki/Torque
The branches and leaves on the tree kinda act like a sail. This means they ‘catch’ more wind than a human, which is much more aerodynamic. If you wore a wingsuit or parachute or something similar, you would also sway in the wind.
A tree is like a human holding on to a windsail in a stiff wind, and not being able to ‘lean in’ to the wind at all.
People go inside when the wind goes over 60mph.
Trees don’t.
When people go outside in actual storm force winds, they will certainly not wander around. They will get knocked down and driven into trees, cars and buildings which have no problem standing up to the same winds.
The answer is that you are looking at trees that have been outside during the part of the storm you went inside for.
Storms knock over houses, and tip over cars. Of course they will batter people silly enough to go out in them.
Latest Answers