There are a couple of often repeated ideas that I’ve always questioned:
Can a bullet shot from a gun change direction significantly after hitting a leaf? It would seem that the force and momentum of a bullet would be so large that a leaf in the way would be almost irrelevant. But I’ve heard from many people in many forms of stories about how a bullet shot in one direction changed angle significantly upon hitting a leaf (even completely reversed direction in one case)
Is jumping into water (in a flat position) from a great height just like jumping onto pavement? I’ve done belly flops into a pool and I imagine that a belly flop onto pavement would be much worse. Plus, why would a flat position change anything? Shouldn’t a diver going in vertically also be impacted similarly?
#2 is true (sort of) from a sufficient height. At a slow speed, like diving off the edge of a pool, the water has plenty of time to displace underneath you, cushioning the impact. The faster you go, the less time the has for displacement and the more sudden your stop is. The pavement is used as an example of something that would always have a sudden stop at any speed. At a high speed, such as someone jumping off of a bridge, the stop is so sudden that you’ll break bones, etc. much like hitting the pavement.
The reason that belly flopping is mentioned has to do with the displacement issue again. The more water than needs to be displaced, and the farther you need to displace it, the more sudden the stop. So a graceful dive is going to be less damaging than a belly flop. That’s true at any speed.
Of course, the statement is a little bit exaggerated. Hitting water is never exactly like hitting pavement. It’s just a way of explaining (to kids, maybe) that you shouldn’t expect to live just because you’re jumping into water - if you get high enough, water will kill you just as dead as the pavement.
The drag you experience when moving through a fluid medium (fluid = a gas or a liquid) is almost entirely due to ram pressure against the forward-facing surfaces of your body (and a related decrease in pressure on the rearward-facing surfaces). This drag is proportional to the density of the fluid: double the density of the fluid, and your drag will double. This drag is also proportional to the square of your speed: double your speed, and your drag will roughly quadruple.
As you fall through the air at terminal velocity (~120MPH), there’s enough drag to equal your weight; for an adult male, that’s around 160 pounds. Now you hit the water, and suddenly you’re moving through a medium with a much greater density than the air. Water is about 800 times as dense, and so your 160 pounds of drag increases by a factor of 800, to about 128,000 pounds. You experience about 800 g’s of deceleration on impact. It’s not exactly the same as hitting concrete, but it’s still fatally violent. People who fall from great heights into water don’t necessarily drown; they often die from blunt-force trauma - skull fractures, internal hemorrhaging, etc.
Having flat surfaces facing forward (e.g. belly-flopping) assures maximum ram pressure on those surfaces. If you want to minimize the ram pressure and maximize your chances of survival, you need a streamlined shape (notice how pointy figher jets are), so you try to go in toes-first or hands first. Problem is that it’s just about impossible to keep your arms/hands pointed properly against that kind of force; they’ll buckle almost immediately, and your skull will take the impact with the water. Your feet and legs will only be slightly more able to withstand it. No matter the orientation, falling from great height into water is difficult to survive.
On the first question, it depends on what you mean by “significantly”. For a long enough range and a small enough target, it’s possible that hitting a leaf en route might be enough to turn what would have been a hit into a miss, and that’s arguably significant. If you mean turning a right angle or rebounding backwards, though, there’s no way. Even if the leaf were as hard and rigid as plate steel, it couldn’t turn a bullet around unless its mass were greater than that of the bullet. And for real leaves that’ll flex and tear, you’d need the mass of the portion of the leaf that’s moving significantly to be greater than the bullet.
Depends on speed, the shape of the bullet, the type/thickness of the leaf, the angle at which it hits, wind velocity, etc . . . and what you mean by “significantly.”
Hang up a bedsheet on a clothesline, and hit it with a baseball bat. See if it deflects, or stops, the bat. I would expect that a leaf might do the same thing to a bullet. But it would depend on one important factor. If the bullet penetrates the leaf, then it would have little effect. But if the leaf withstands the bullet loses as much energy as it takes to displace the entire weight of the leaf. A fairly large leaf might weight more than a small bore bullet.
If your baseball bat does not tear a hole in the bedsheet, it has to displace the entire weight of the bedsheet to reform it into a different shape with a depression where the bat hit it.
Shot into the fully-leafed canopy of a deciduous tree, the bullet might not have enough force to make through a number of leaves equal to the weight of the bullet, unless the leaves were so fragile that they easily split apart from the bullet force. Fresh green tree leaves can be pretty tough…
First, it’s unmanly for a marksman to admit to poor marksmanship. So an excuse for missing a shot is useful. “Hey, it got deflected by a leaf!”
Second, there was a LOT of resistance to the Army accepting the M-16 and it’s .223 round. So a rumor went around that the .223 (or 5.56mm x 45) round was so bad that a leaf could deflect the 55 grain bullet. It’s bojive though. Sure, it was a 55 grain bullet but it had a muzzle velocity of 3,300 ft/sec. THAT is high velocity.
Swing a telephone pole at the speed of sound and come back to us.
Bullets being deflected are a matter of momentum, which is the mass times the velocity. At 4400 km/hr, bullets have a hell of a lot more momentum than leaves.
The leaves tear really, really easily, and even if you had kelvar leaves, they would get knocked aside as they are only being held by their stems.
It’s not a matter of momentum; it’s a matter of mass. Shoot a bullet straight at something rigid with the same mass, and the bullet will stop. Shoot it at something with a greater mass, and the bullet will come back at you.
Leaves aren’t rigid. Some thicker leaves, from certain directions (like end-on to the central rib of the leaf, for instance), can be pretty tough, though. I’d say a great deal depends on the type of leaf and what direction the bullet hits it from.
Maybe I’m misunderstanding what you’re trying to say. In a perfectly inelastic collision, if you shoot a bullet straight at something with the same mass as the bullet, wouldn’t they both end up moving in the bullet’s original direction, with half the original speed? And in a perfectly elastic collision, the bullet would stop dead while the target sped away at the bullet’s original speed and direction?
Rigid things will generally be elastic, or very close to it. And yes, I should have specified that in addition to the bullet stopping, the thing that stopped it would also go flying off.
A slug bouncing off a single leaf is hard to believe.
Hunters often worry about a bullet’s “stability in the bush,” meaning whether or not it will go straight and true when going through bush, or when it hits the target. One gun magazine article did experiments using aligned hardwood dowels as targets. They tried shooting different bullets and different slugs for a given cartridge. Differences weren’t so pronounced.
More likely it’s the bullet’s imperfection that causes it to lose stability, even when hitting a soft light target. Stories abound of bullets bouncing more than 90 degrees going through reeds and leaves (several leaves mind you.) Elmer Kieth shot a mountain goat with a 30-'06 and the bullet went in just 3 inches, turned, and exited within two inches of the entrance wound.
A key point though is how much of the mass of the leaf is going to be opposing the bullet. If the leaf tears near-instantly such that the bullet passes through without having to deflect any significant part of the leaf, it isn’t going to matter that the whole leaf weighs a substantial amount in comparison to the bullet .
Right, like I said earlier, "And for real leaves that’ll flex and tear, you’d need the mass of the portion of the leaf that’s moving significantly to be greater than the bullet. ".