soda

hahahaha... just adding more fuel to the confusion! Yes, you're right.

Merton: I agree with everything you said about the horizontal component. Now that you've got that off your chest, go find a woman or a saddle and forget about this thread.

rustychain

My worst crash in terms of injury was at 12mph (I think) wet leaves are like ice. Broken collerbone. In contrast I went down at 20mph plus trying to avoid a car that ran a light. I slid, lost some skin, scratched my bike and helmet but was OK. I have heard stories from other long time riders that agree (providing you don't slam into something hard. In that case your toast. Its all in how you stop, not your speed as you go down. If anyone would like to be our test dummy we could put it to the test!

pablo27

at 30 mph, the kinetic energy your body has relative to the ground IS 9 times that going 10mph.

momentum direction is mostly forward, until you "touch" the ground... and oh this is where your linear momentum and kinetic energy might be dissipated slowly and result only in a road rash if only you could slide to a stop, but no

the friction of your butt "touching" the ground creates a moment with you momentum vector,... and yes that linear momentum is converted to angular momentum

now tumbling at just under 30 mph, your legs and arms spinning about your center of mass (roughly), you end over end gaining more angular momentum

depending on the specific direction of the head or legs at impact with the ground or tree or whatever... the kinetic energy of your head or leg is transferred abruptly to the ground or tree or whatever through large forces exerted over short distances

whatever you feel, if you can feel anything, feels terrible

H23

Okay, that's fine. Now, do you define initial impact as the instant in time _before_ the body hits the ground or the instant in time when the body experiences a peak force?

If the latter, you are missing a horizontal force on your diagram.

The horizontal force, to first order, is uN. Where u is a coefficient of friction and N is the peak force of impact (normal to the ground).


In short, you have to account for friction because it adds another force on the diagram.

53-11 alltheway

Kind of like what we all learned in high school.....

A bullet dropped from your hand at 3 feet is going to hit the ground at the same time as a bullet shot from a gun also at 3 feet.

SEE Post #40.....which is was responding to. Gun barrel is parrelel to ground, not pointed at ground!

Chucklehead

um..no...

alanbikehouston

The evidence of a drug problem in American high schools is kinda hard to ignore.

Trekke

That is likje saying if a bullet starts out above you it wont hurt you when it its you. Good to know.

slvoid

In a vacuum, yes, both bullets would fall at the same time. And on a flat surface.
But on earth, you have aerodynamic effects acting differently on both bullets. Plus the surface of the earth isn't flat, you'll have to fall slighty farther for the moving bullet than the stationary one due to the curvature of the earth. In fact, if your bullet is traveling fast enough, it'll have so much distance to "fall" that it'll never stop falling, that's called being in orbit.

53-11 alltheway

The whole point of that "lesson" was that the horizontal velocity component doesn't affect the vertical component.

If the barrel is parrallel to the ground and at the same height ......both bullets will strike the ground at the same time. The only difference is that one bullet will be right next to you and the other farther away.

53-11 alltheway

These bullets are three feet off the ground......not being shot from the Hubbel space telescope.

53-11 alltheway

You've got to be kidding me. You didn't learn this?

53-11 alltheway

aerodynamic effects will only influence horizonal component not vertical......obviously a hollow point pistol bullet will shed it's velocity sooner than a boat tail rifle bullet (due to hollow point's lower ballistic coefficient).....and it will hit the ground closer to the shooter than the rifle bullet assuming the same initail velocity

Also at three feet.....the curvature of the earth will have almost no effect.

slvoid

You need to take a class in aerodynamics... Better yet, start a similar thread, "Do aerodynamics matter when you're falling", kinda like "crashing downwards at 30mph is same at 10mph".
Why am I even reasoning with the idiot who thinks he can hit 50+ mph on a bike on flat ground...

53-11 alltheway

Assuming the dropped bullet doesn't fall nose first ......they will hit exactly at the same time if dropped at the same height at the same time. Period.

Aerodynamics are the same for both projectiles if the both land on their sides......DUH!!!!!!

JavaMan

If a bullet falls in the forest and there's no one around, will it hit the ground?

53-11 alltheway

Obviously I'm right.....No ****.

slvoid

By your definition, an airfoil, whether moving forward or having no horizontal component, would both fall at the same rate right?
DURRR... obviously you're wrong. Listen, come back when you reach 50mph and we'll talk.

slvoid

If a bullet is fired in the forest and no one's around, will someone eventually get shot?

Chucklehead

the principle works with objects of different weight. in an environment with specific conditions. what you're saying is that a bullet discharged at 1500' per second will hit the ground at the same speed as a bullet that has simply been dropped. or that the discharged bullet travels more than 3' before it begins its accelleration?

JavaMan

Yeah - Wasn't that Greg Lemond?

Chucklehead

the bullet is discharged at a velocity higher than the dropped bullet can reach.

slvoid

What the...

53-11 alltheway

Go get a high school physics book.

Your analogy to a vaccum is used when comparing a feather falling and something heavy like a rock (in a vaccum a feather and a rock will fall at the same rate). Aerodynamics do no matter in a vaccum......therefore a feather (with ****** areodynamics) will fall just as fast as rock.

Now in this case we are not comparing feathers and rocks.......NO, We are comparing two IDENTICAL bullets. Same aerodynamics. Vaccuum doesn't matter.

What you are failing to understand is that the barrel is completely level, not like in real life where you would zero in your scope to adjust for the trajectory to prolong the bullets flight time.

53-11 alltheway

The gun barrel is not pointed down!!!!!!!!!!!!