BIKEPGH MESSAGE BOARD ARCHIVE

Yes, and mostly.

Ouch. Literally. Hope you're OK. How's the bike?

I shielded the bike from harm with my body.

i got stuck in southside works during the first one, hiding under the REI awning... the second set started as i was riding up the hill to my house. that was the pea hail. the golfballs started right after i got inside... whew

I shielded the bike from harm with my body.

......now that's commitment.

The ones we collected from outside the office where the size of (stage 1) quite large peas and (stage 2) grapes. No golfballs in Sq. Hill. I waited to ride home.

Hail in the Perrysville Park & Ride lot, Ross Township, around 5:10 pm on March 23, 2011. Most were about dime sized, but several nickel-size and a couple quarter-size. Elsewhere in the area, hail of 1.75" or greater fell.

I saw on The Weather Channel that McKeesport got 2in hail. I saw about golf-ball size in East Liberty....because it was hitting my windshield.

I sat the first round out by getting a haircut. I'd like to think of it as multitasking. The second round started about a half mile from my parent's house, so free dinner. Not bad for a crappy afternoon:-)

http://www.hulu.com/watch/146354/the-simpsons-golf-ball-sized-hail

I'm logging out! It's not safe on this board!

I was riding my scooter to work. At one point, I was looking up a hill with paintball sized hail rolling down it. By the time I got there, it increased to quarter-sized hail, and my thighs were covered with welts.

Another reason to wear a helmet.

Welts:

Owwww!

Damn this weather sucks.

Yikes!! I concur with edmonds59.

from somewhere around CMU

hail is so creepy looking.

Psh you havent lived until you've witnessed the storms in the central plains.

A hail ball being measured by a digital micrometer - it is very nearly redundant to even mention that is from "somewhere near CMU". Ha, ha!

Sadly, that is the second photo of hail being measured by a micrometer I saw in the past 24 hours. The other was from a cyclist--though I'm not sure he posts here.

I want to see an equation that solves for the energy carried by a given size of hail ball, including accounting for the terminal velocity of the given size of hail ball.

edmonds want to see an equation that solves for the energy carried by a given size of hail ball, including accounting for the terminal velocity of the given size of hail ball.

I'm guesing wind will increase impact velocity.

Some cool hail anecdotes, including terminal velocity.

Old fart note: You kids today don't have hail like when I was young.

http://www.history.com/this-day-in-history/hail-kills-english-troops

In April 1360, Edward's forces burned the Paris suburbs and began to move toward Chartres. While they were camped outside the town, a sudden storm materialized. Lightning struck, killing several people, and hailstones began pelting the soldiers, scattering the horses. One described it as "a foul day, full of myst and hayle, so that men dyed on horseback [sic]." Two of the English leaders were killed and panic set in among the troops, who had no shelter from the storm.

The heavy losses suffered by the English were seen by many as a sign from God. King Edward was convinced to negotiate peace with the French.

The same source says Boostuv is right:

The largest hailstone recorded in modern times was found in Aurora, Nebraska. It was seven inches in diameter, about the size of a soccer ball. Hail typically falls at about 100 miles per hour.

I would think that hail would be somewhat less than 100 mph - human terminal velocity is about 130 mph, and we're about as dense as water.

Terminal velocity for a mouse is low enough that they will scamper away.

The terminal velocity of the hail will increase with the size of the ball. We could test the velocity of the hail by firing ice pellets at reddan until we replicate the welts.

It's interesting that the large hail ball in the micrometer photo is made up of smaller balls of similar size, so there must be a cloud of hail balls that are faily stable in the rising air column until they start to lump together into large balls that exceed the velocity of the rising air column and start to fall through it. There is probably something to be learned about the formation of the universe from studying hail. It looks like a little planet.

We could test the velocity of the hail by firing ice pellets at reddan until we replicate the welts.

A fine plan.

Hee, hee!

I may be the only one who enjoyed the hail??? I had a pretty tough day at work and the hail hit me right on the highway stretch between blawnox and Harmarville. I forgot my jacket at work, so I was riding in just a tshirt. I pretty much got scuked into the energy and passed up the few places that I could have taken cover. Im pretty sure that every car that passed me thought (or realized, i suppose) that I am a bit crazy

On a side note, hail hitting the handlebars at just the right angle sounds pretty cool, almost like a xylophone!

phooey. real geeks read their own vernier calipers and don't need a digital device to do it for them.

Pshaw. Real geeks measure the shadow of the object, then calculate the angle of incidence and distance from occluding object to determine a scaling factor.

acshully, I hate my digital calipers right now because the battery is dead and they're not a vernier scale so I have to guess. And I can't do the math to figure the internal diameter of a hole from its shadow

Caught some welts from this too. Ow.

Ooh, test subject #2!

@beast: I find after a bad day, I, too, enjoy a good ol' weather beat down. I'm always reminded of Lt. Dan lashed to mast during the storm in Forrest Gump....

^ check out the paintings of JMW Turner. He definitely enjoy a good weather beat-down or two.

@edmonds59 --

"It's interesting that the large hail ball in the micrometer photo is made up of smaller balls of similar size, so there must be a cloud of hail balls that are faily stable in the rising air column until they start to lump together into large balls that exceed the velocity of the rising air column and start to fall through it. There is probably something to be learned about the formation of the universe from studying hail. It looks like a little planet."

It's a chaotic system or structure with the scaling that is part of such systems. So yes, if you replicated the system out to a universal level, you might find something in the little hail ball that is also at work on the universal scale. The only catch here is that I understand the the chaotic structure of weather is somewhat unique. And of course, universe could have its own chaotic structure that is unique to it.

P.S. Can someone tell me how to italicize quotes beccause I seem to be too dumb to figure it out on my own?

cdavey, it goes like this:

[em]whatever you want to emphasize[/em]

only, replace the [ ] with < >

@Pseudacris --

Thanks.

From Gordon:

I have to agree with RubberFactory that the hail is kind of creepy looking.

I want to see an equation that solves for the energy carried by a given size of hail ball, including accounting for the terminal velocity of the given size of hail ball.

understand that i am no fluid dynamicist, but here goes! assumption: hail ball is a rough sphere, with a drag coefficient of about 0.45 in normal atmospheric conditions.

so, terminal velocity occurs when the force of gravity equals the drag:

mg = (1/2)pv^2dA

so:

v^2 = 2mg/(pdA)

where m is the mass of the hailstone, p is the mass density of air, d is the drag coefficient, and A is the area of the largest cross section of the hailstone. we'll presume a constant density of the ice, at about 916.7 kg/m^3, and a dencity of air of 1.27 kg/m^3. if we translate the mass and area into equations of r, we end up with:

v^2 = (8/3)rgq/pd

where q is the density of ice. by this, we can calculate that:

v = 208 * r^0.5 m/s

so, for a hailstone about 1 inch (0.0254 m) in radius, the terminal velocity is about 33.22 m/s or 74.31 mph. such a stone would have a kinetic energy of:

E = (1/2)mv^2

of course, with a mass of about 0.06 kg, so an energy of about 34.73 joules.

incidentally, the drag coefficient we assume has a pretty big effect on the results. for example, if we assume a d = 0.2, the terminal velocity would be 109.4 miles per hour.

@HV: I was just going to say that. Really.

Awesome!, that's what I was looking for. I just didn't want the board to turn into all Milton and chemistry and helmets.

The biggest unknown variable I can think of is, at what altitude will the hail ball drop completely out of the rising column of air and start gaining speed to terminal velocity relative to the surface of the earth and not the air column. But I think we can assume that happens high enough that the ball will attain full velocity.

i think that's a safe assumption, since with a terminal velocity of 34, it would only need to be falling for about 3.5 seconds. that's a fall of about 61 meters, or about 200 feet.

If the updrafts are strong enough the hail doesn't necessarily drop out of the bottom, it gets ejected out the top. If it doesn't clear the column, it takes another trip which is how it keeps growing, and picks up that weird bumpy form.

Amazing story about a pilot that got caught in an updraft after ejecting: http://en.wikipedia.org/wiki/William_Rankin

Help I'm being educated!!

Is this the right thread to ask if one should wear a helmet whilst riding in a hailstorm, or does the size of the hail make a difference?

WWVD?

(what would vikings do?)

I do not wear a helmet but would definitely recommend one in a hailstorm. Those damn things hurt. I joke that I have been experiencing post concussion syndrome as a result of last week.