Anyone here good at physics?

[BlackCatWhiteCat]

I have a question for you. Purely hypothetical of course.

So you have a solid, 2 pound ball of glass. For our purposes let's call it a candleholder. Now let's say this 2 pound candleholder fell a distance of 7 feet from something like a closet shelf. What kind of impact would you expect that on, I don't know....a human foot? My mother guessed 30 pounds. Hypothetically.

I doubt it's that much.

[Rett Mikhal]

You don't specify pound force or pound mass. I'll assume it's pound force since that is what most people know as 'a pound'. Pound force is slugs (standard unit of mass) times gravity.

Since F = M*A, and we've already stated that pound force is Mass times Gravity (which is an acceleration), the ball has 2 pounds of force.

Now if you want to know how much mechanical energy is transfered, then it is the potential energy, PE.

PE = M * G * H. Once again, M and G are already multiplied, so it turns into:

PE = 2 * 7 ft. So 14 foot pounds. Since there are no other outside forces, KE should be PE (ignoring air resistance since it only falls 7 feet.) So:

V = (2 * G * H)^1/2

V = (2 * 32.2 ft/s^2 * 7 ft)^1/2

V = 21.2 ft/s

And finally Kinetic Energy = 1/2 * M * V^2. I'll divide 2 pound force by 32.2 to get slugs.

KE = 1/2 * (2/32.2) * 21.2^2

KE = 13.96 foot pounds.

That's just the energy though, not the force. You'd need to measure how far the candleholder bounced to get the total force.

hyperphysics.phy-astr.gsu.edu/hbase/flobi.html

[BlackCatWhiteCat]

Jun 11, 2008 19:47:44 GMT -5 Rett Mikhal said:

That's just the energy though, not the force. You'd need to measure how far the candleholder bounced to get the total force.

hyperphysics.phy-astr.gsu.edu/hbase/flobi.html

Sorry..I was in a state of white pain at that point. Didn't manage to check how far it bounced off of my foot! From what I remember, i picked it up less than a foot away from my foot. Thank you, though. I guess I can assume that I sustained roughly the amount of 14 pounds being dropped onto my foot, then?

Yeah I'm done denying it. I stored that thing in the top shelf of my closet like an idiot. I don't suppose it broke anything, though it's pretty painful. Getting better all the time. I'm notorious for not wanting to go TO (there, happy?) the doctor, and since I can walk on it (albeit with a little pain if I move it certain ways) I've decided it's not serious enough to go to the doctor for. Fourteen pounds of force, though.....ack. Sure felt like it.

I'll spend my time here in the bed checking out that link.

[bladestarr]

It's honestly not the force or mass that really kills you though, it's the density vs. the surface area that it actually hit. If it was a pillow or blanket of the SAME mass and weight that fell at the same speed, it wouldn't hurt nearly as bad. Not just because it's soft, but because those materials are LESS DENSE, and they would hit a much LARGER surface area.

It's the same effect that lets those Indian dudes lay on a bed of nails. It LOOKS impressive, until you realize that they aren't really putting much weight on each nail... so it really doesn't hurt that much more than laying on gravel. Getting on and off however, that's the tricky part.

[StarOpal]

Jun 11, 2008 19:57:59 GMT -5 BlackCatWhiteCat said:

Sorry..I was in a state of white pain at that point. Didn't manage to check how far it bounced off of my foot! From what I remember, i picked it up less than a foot away from my foot. Thank you, though. I guess I can assume that I sustained roughly the amount of 14 pounds being dropped onto my foot, then?

Yeah I'm done denying it. I stored that thing in the top shelf of my closet like an idiot. I don't suppose it broke anything, though it's pretty painful. Getting better all the time. I'm notorious for not wanting to go do the doctor, and since I can walk on it (albeit with a little pain if I move it certain ways) I've decided it's not serious enough to go to the doctor for. Fourteen pounds of force, though.....ack. Sure felt like it.

I'll spend my time here in the bed checking out that link.

1) How long ago did this happen?

2) Are you getting super dark purple bruising?

[Buttercup]

To answer the original question:
Depends. If it lands on someone else's foot, it is very light, does no real damage, and is just funny. If it lands on your own foot, it's weight is equal to the mass of Murcury⁴.

[BlackCatWhiteCat]

Jun 11, 2008 20:28:39 GMT -5 Buttercup said:

To answer the original question:
Depends. If it lands on someone else's foot, it is very light, does no real damage, and is just funny. If it lands on your own foot, it's weight is equal to the mass of Murcury⁴.

Hehe....well unfortunately for me it's the latter.

[BlackCatWhiteCat]

Jun 11, 2008 20:08:03 GMT -5 StarOpal said:

1) How long ago did this happen?

2) Are you getting super dark purple bruising?

1. It happened yesterday.

2. Yes, immediately the area began swelling and there was a BLACK (I emphasize this because I've been bruised but never seen such a black color on human skin)dot about the size of a pencil eraser in the middle of a reddish swollen area. This landed almost right on the tendon that runs from my big toe, by the way. It took about 30 minutes for the black to turn to red. Today the swelling is down and the area is much less noticeable. I have more freedom of motion in my foot, but flexing my toes far back hurts, as does flexing my foot far back,and curling my toes very much, and certain other movements hurt (hard to explain, since these certain movements occur by accident and I'm not willing to keep testing my foot on purpose). I think maybe the tendon is just bruised.

Unfortunately this puts a huge damper on my DDR workout regiment.

[BlackCatWhiteCat]

Jun 11, 2008 20:03:11 GMT -5 @bladestarr said:

It's honestly not the force or mass that really kills you though, it's the density vs. the surface area that it actually hit. If it was a pillow or blanket of the SAME mass and weight that fell at the same speed, it wouldn't hurt nearly as bad. Not just because it's soft, but because those materials are LESS DENSE, and they would hit a much LARGER surface area.

It's the same effect that lets those Indian dudes lay on a bed of nails. It LOOKS impressive, until you realize that they aren't really putting much weight on each nail... so it really doesn't hurt that much more than laying on gravel. Getting on and off however, that's the tricky part.

Well all I can tell you about that is where it hit my foot. If you put your finger between your big and index? toe and run it back up your foot you'll hit a bony knob. So did the candleholder.

[StarOpal]

Jun 11, 2008 20:41:56 GMT -5 BlackCatWhiteCat said:

2. Yes, immediately the area began swelling and there was a BLACK (I emphasize this because I've been bruised but never seen such a black color on human skin)dot about the size of a pencil eraser in the middle of a reddish swollen area. This landed almost right on the tendon that runs from my big toe, by the way. It took about 30 minutes for the black to turn to red. Today the swelling is down and the area is much less noticeable. I have more freedom of motion in my foot, but flexing my toes far back hurts, as does flexing my foot far back,and curling my toes very much, and certain other movements hurt (hard to explain, since these certain movements occur by accident and I'm not willing to keep testing my foot on purpose). I think maybe the tendon is just bruised.

Hmmmm...

Well since you hate going to the doctor so much, I'm sure some random internet stranger saying you should get it checked out won't mean much. BUT if the dark bruising (even if there's little or no swelling) returns, get to the doctor. Otherwise, try not to favor it too much, or you'll end up with a messed up back.

Not that I've ever done anything like that to my feet.... *innocent whistling*

[Hucklebubba]

Jun 11, 2008 19:57:59 GMT -5 BlackCatWhiteCat said:

I'm notorious for not wanting to go do the doctor. . .

Please fix this before I say something that will get me scolded.

[bladestarr]

Jun 11, 2008 23:17:03 GMT -5 Hucklebubba said:

Jun 11, 2008 19:57:59 GMT -5 BlackCatWhiteCat said:

I'm notorious for not wanting to go do the doctor. . .

Please fix this before I say something that will get me scolded.

At this point.... I'm convinced she does it on PURPOSE. ;D

[BlackCatWhiteCat]

*has tears in her eyes, she's laughing so hard* Why didn't someone tell me sooner!? I bet you've all been laughing at me over your cups of coffee and whispering about it in private messages. I just know it! You know, because I'm that important. Right.

And no I DO NOT do it on purpose, Phil. I can't help it that you men have dirty minds and jump on any of my typos/accidental innuendos like rabid hyenas on a carcass.

SHAME!

*trudges along to fix yet another embarrassing typo mishap*

[Rett Mikhal]

Jun 11, 2008 20:03:11 GMT -5 @bladestarr said:

It's honestly not the force or mass that really kills you though, it's the density vs. the surface area that it actually hit. If it was a pillow or blanket of the SAME mass and weight that fell at the same speed, it wouldn't hurt nearly as bad. Not just because it's soft, but because those materials are LESS DENSE, and they would hit a much LARGER surface area.

It's the same effect that lets those Indian dudes lay on a bed of nails. It LOOKS impressive, until you realize that they aren't really putting much weight on each nail... so it really doesn't hurt that much more than laying on gravel. Getting on and off however, that's the tricky part.

Yes because stress is force divided by area. The denser something is, the more mass, and the more force by gravity. The less area, the greater stress applied on whatever object it hits. If it had been a tapered cone, it would have easily pierced your foot because of the extremely tiny area of a taper point. On the other end, if it's a LARGE object, the relatively small area of your foot works against you, because all the force has to go somewhere and guess where it will choose to.

Jun 12, 2008 17:34:43 GMT -5 BlackCatWhiteCat said:

*has tears in her eyes, she's laughing so hard* Why didn't someone tell me sooner!? I bet you've all been laughing at me over your cups of coffee and whispering about it in private messages. I just know it! You know, because I'm that important. Right.

And no I DO NOT do it on purpose, Phil. I can't help it that you men have dirty minds and jump on any of my typos/accidental innuendos like rabid hyenas on a carcass.

SHAME!

*trudges along to fix yet another embarrassing typo mishap*

I just want to mention this is the second one I've seen and I was never tempted to make a Huckle joke at you.

[Hucklebubba]

Yes! I have had a joke-type named after me! Today a joke-type, tomorrow a sundae!