Boy Hit By Meteorite Travelling At 30,000mph

[greree]

A news article I read today. Quote:

 

"The white-hot meteorite bounced off the schoolboy's hand and hit the ground so hard it left a foot-long crater in the tarmac - as well as a three-inch scar on his hand."

 

If a meteorite traveling at 30,000 mph hit someone's hand, wouldn't it take it off, rather than bounce off?

[Mokele]

If his hand deflected as a result, perhaps it would just leave a scar.

[greree]

If his hand deflected as a result, perhaps it would just leave a scar.

I'm not sure I understand your answer. A bullet traveling 1000 feet per second wouldn't knock someone's hand out of the way, it would pierce it. A meteorite roughly the size and shape of a bullet traveling 44,000 feet per second certainly wouldn't knock someone's hand out of the way, and it certainly wouldn't bounce off and then strike the ground hard enough to leave a two foot crater.

[iNow]

It also depends on the angle at which the hand was hit. Based on what I just read, it doesn't look like the strike was orthogonal to the hand, but instead nearly parallel. The picture of the wound seems to confirm that... of course, if it truly was a meteorite.

 

 

http://news.bbc.co.uk/cbbcnews/hi/newsid_8090000/newsid_8097700/8097729.stm

[Ophiolite]

I'll offer an iron clad (or at least a carbonaceous chondrite) gauruntee that the meteorite was not still travelling at 30,000mph when it hit the boys hand. Simplifying, we can split the meteorites/asteroids into three velocity classes.

 

1. Damnably big, like a dinosaur killer, that still has it's ass end hanging out of the atmosphere when the front end hits. Velocity is not reduced in any noticeable way by the atmosphere.

2. Medium sized items of a few thousand tons, which will explode in the air through differential heating and the fact that most asteroids are rubble piles. Some of the remaining components will come in fast, but most will be considerably slower than 30,000 mph.

3. Small objects waying only a few kilos that come in either as discrete pieces or form from the break up of larger bodies will hit at, or not much more than, terminal velocity. Depending upon shape this is going to be slightly more than 100mph.

 

The boy got hit by an object from the third class, not something faster than a speeding bullet.

[insane_alien]

its more likely that he got hit by debris from the crater.

 

as it supposedly left a decent sized crater(though i haven't seen any pictures of this) then there was obviously something going pretty fast and with a fair mass behind it. at the speeds considered, it would be impossible(for a human) to tell which happend first, the cratering even or the debris striking hand event.

 

i also think the 30000mph think is complete bunk. someone on orbiter forum done a rough calculation to show the heating power on the meteorite at that speed would be 300 odd mega watts. it would have been vapourized almost instantly.

[swansont]

The 30,000 mph claim was probably some reporter doing a shoddy job of research for the story.

[John Cuthber]

I don't know the terminal velocity of a pebble, but it can't be that different from a hail stone of the same size.

Assume, for the sake of doing a rough calculation, that the meteorite is 9 times denser than ice (not a bad guess if it's iron).

I'm pretty sure that the viscous drag rises as the square of the velocity and, for an object 9 times denser, the force would be 9 times greater so the velocity would be 3 times greater.

 

A bit of searching gave me this data

"Research has found that a hailstone's terminal velocity is roughly proportional to the square root of its diameter, with a diameter of 1 cm corresponding to a terminal velocity of 50 km/h (Munich Re, 1984)."

so I gues about 150Km/Hr or 100 mph is the right ballpark as ophiolite said. (or rather less if it's not as dense as iron)

[Cap'n Refsmmat]

The Bad Astronomer's take:

 

Then things get really confusing. The article claims the boy was hit first, then the object hit the ground, carving out a one-foot crater. I’m having a hard time with that: if it hit the ground hard enough to blast a small crater, then it should’ve done a whole lot more damage to the boy than cause a three-inch scar. I suspect that, if we take the crater and all that at face value, it hit the ground first and then he was hit by shrapnel.

http://blogs.discovermagazine.com/badastronomy/2009/06/12/a-boy-claims-he-was-hit-by-a-meteorite/

 

Which does match up with what we're suspecting here.

[stereologist]

At 30000 mph an object is traveling at around 45000 feet per second.

 

How could anyone tell the order of events when the time between them is x/45000 seconds? Here x is the distance from the hand to the impact crater.

[Ophiolite]

At 30000 mph an object is traveling at around 45000 feet per second.

 

How could anyone tell the order of events when the time between them is x/45000 seconds? Here x is the distance from the hand to the impact crater.

As noted above no objects involved in this incident were travelling that fast at the time of impact, or in the immediate aftermath.

[greree]

The 30,000 mph claim was probably some reporter doing a shoddy job of research for the story.

All reporters do a shoddy job of research for their stories. Have you ever read a reporter's story on Quantum Teleportation?

[Shadow]

...it doesn't look like the strike was orthogonal to the hand...

 

Couldn't have been. A person walks with his arms (and hands) along their body, and a meteorite falls down. The article said nothing about him scratching his head at the time. Just adding to the pot.

[swansont]

All reporters do a shoddy job of research for their stories. Have you ever read a reporter's story on Quantum Teleportation?

 

I take it you are not familiar with my posts on the subject, either here or on my blog. Yes, I have.

[GutZ]

Here is a good lesson for me to learn I guess...ok so...

 

Is acceleration constant with gravity? and how does atompshere and gasous elements play in the role of slowing objects down. Would an object be traveling faster if it were say 10,000 km above the earth surface vs soemthing that is falling from 100km from the surface?

 

I know two objects regardless of mass (from a low point) dropped will fall at the same rate because of gravity...

 

but does the speed of say a small meterite say the size of a pebble that doesn't disengrate due to the friction if air and such have the samw speed as hail of the same size?

[swansont]

but does the speed of say a small meterite say the size of a pebble that doesn't disengrate due to the friction if air and such have the samw speed as hail of the same size?

 

Once you add air resistance mass matters, but the speed range is in the 100's of km/hr for any reasonable numbers.

[iNow]

I don't know the terminal velocity of a pebble, but it can't be that different from a hail stone of the same size.

But, is terminal velocity really a factor to be considered at all here since the meteor is coming into the atmosphere with a very high velocity already?

 

AFAIK, terminal velocity essentially describes the maximum amount that gravity can accelerate an object before drag disallows further acceleration.... it does NOT describe how quickly an object can go (especially when said object was hurdling through space with a velocity much above terminal velocity to begin with).

 

Is this correct... can terminal velocity essentially be disregarded since the meteor is not being accelerated to a higher speed... or am I perhaps missing something blindingly simple, and the drag would be enough to slow the meteor to this terminal v?

[Ophiolite]

iNow, you are missing something. For example, you are missing reading my first post in this thread. Although simplified it accurately describes the situation: small meteorites are slowed to approximately terminal velocity.

[Daecon]

As soon as I saw this thread I thought of:

 

18 Times the Speed of Light

 

Because F**K YOU, Einstein!

 

And I lol'd.

[Ophiolite]

Transdecimal,

the speed of light is approximately 670,000,000 mph. That is over 22,000 times faster than the alleged speed of the meteorite. Einstein was never in any danger.

I suggest you delete your post to remove further embarrassment.

[iNow]

iNow, you are missing something. For example, you are missing reading my first post in this thread. Although simplified it accurately describes the situation: small meteorites are slowed to approximately terminal velocity.

 

Ah yes... So I am. Thanks for the reminder. I had read your post, but seemed to have missed that particular bit (or, failed to commit it to memory). Seems my amygdala/hippocampus needs to be re-indexed.

[swansont]

Transdecimal,

the speed of light is approximately 670,000,000 mph. That is over 22,000 times faster than the alleged speed of the meteorite. Einstein was never in any danger.

I suggest you delete your post to remove further embarrassment.

 

The sentiment is valid, IMO. That was the scroll when the shuttle disintegrated upon re-entry, and falls under the same category of carelessness of checking to see if the numbers were reasonable.

 

The headline didn't remind me of that particular fiasco, but it easily could have.

[GutZ]

Delete this please I totally should of read Ophiolite post again....

 

*wears dounce hat*

 

It all makese sense now.

 

The velocity of a large meteor will have it's kinetic energy from like an explosion in space right like a super nova that blast debris around? and since there is no air resistance it just keeps going till it hits something?

 

whatever that I can find out on my own.

 

Thanks everyone!

Edited June 15, 2009 by GutZ

[Mokele]

Basically, for a falling object in the atmosphere, there's two forces, drag and gravity. You already know gravity, but the force of drag has this basic equation:

 

Fd = 0.5 * (density of fluid) * (velocity)^2 * (Coefficient of Drag) * (frontal surface area)

 

Most are pretty self-explanatory except the drag coefficient, which is an empirically determined measure of how much drag a surface produces (it's this term that reflects the change in drag between a ball and a cube of the same size). This is also a bit simplified - there's a lot of little details this glosses over, but it works for a first approximation.

 

Basically, if you double the speed the drag increases fourfold, and the drag on very fast objects is very, very high. Big objects also have more area, thus more drag. And the denser the atmosphere, the greater the drag.

 

Thus, as a meteorite falls from space, at first it's just subject to gravity adding to the initial speed. But as the atmosphere gets denser, it's subject to increasing drag, and due to the high speed, the drag is tremendous.

 

Imagine two spheres, both of the same density, falling at terminal velocity, which means the forces of gravity and drag are equal. If the bigger one is twice the diameter, it has 4 times the frontal surface area (because area is a function of linear dimensions squared), thus 4 times the drag. But it has 8 times the mass, thus 8 times the gravity. As a result, it will have to go a bit over 40% faster to balance the forces (meaning a 40% higher terminal velocity).

[GutZ]

So that's why a skydiver who is parrellel to the ground (i.e. | |O) has more drag than when he/she is perpendicular to the ground ( --- |O) and less speed..correct?