If you were shot by a grain of sand(at lightspeed)

[dainthomas]

Originally posted by: YOyoYOhowsDAjello

Originally posted by: hiromizu

Originally posted by: YOyoYOhowsDAjello

Originally posted by: hiromizu

Originally posted by: isekii

Originally posted by: hiromizu
I think you guys are thinking way too scientifically to the point where you can't even get realistic answers. In reality, you'll feel a small pinch and the grain will bounce right off. Nothing more, nothing less.

If at all else i think it'll barely penetrate the skin and you should be able to just flick it off

I think you're pushing it there. A grain of sand won't penetrate your skin.

If a spec of paint traveling at 3.6km/sec can wreck a $50,000 window on the space shuttle, I would think that a grain of sand a some percentage of 300,000km/sec could penetrate your skin 😉

Yea but a space shuttle is flying at a few hundred miles per hour in space. In this case you're not moving and there's air n stuff to cause resistance. It's all relative.

If it's moving at a certain speed at the moment of impact, why does it matter if you're in a vacuum or not up until that point?

I believe the question was assumed to be in a vacuum since in an atmosphere you'd also have to deal with the effects of a shock wave. Most of these kinds of physics questions are assumed to be in a vacuum for simplification anyway.

 

[RESmonkey]

Originally posted by: RESmonkey
I'm going to work this out using mechanics for an inelastic and elastic collision. BUT it's probably not going to be accurate since things moving at such speeds are not in the realm of Newtonian mechanics, but left for QFT, which I don't know, yet.

Ok this is probably wrong because I didn't take in account the make up of the human body, it's compression properties, etc. Just a simple physics thing:

Inelastic:

Mass of grain of sand -> 6.3E-7kg
mass of random human -> 75kg
speed -> (.999999999)(3E8 m/s)
(6.3E-7kg)(.999999999)(3E8) = ( 75kg + 6.3E-7kg)(vfinal)

vfinal -> 2.52 m/s

Elastic:

Dunno, depends?







The sand has a kinetic energy of about 94 Joules.



Can someone help me out here?

 

[OCGuy]

We get hit with radiation particles that split our cells on a daily basis.

 

[rudder]

Originally posted by: amdhunter
Depends. Does the grain of sand take off?

Yes, the treadmill cannot operate at the speed of light.

 

[polarmystery]

it would destroy you. To those saying it wouldn't are wrong.

 

[yhelothar]

Originally posted by: joshsquall

Originally posted by: astroidea

Originally posted by: Train
If you think about the bullet example I mentiond above. Obviously sand is a lot less mass, but theats WAAAAYYY offset by the exponential growth in speed.

Force = Speed x Mass, therefore a grain of sand at light speed is 1000000000 X times more force than a hypersonic 50 cal round.

If it flew within a thousand yards of you, you'd be ripped to shreds in under a second.

fail.. f=ma.. a=0, f=0
on the other hand, momentum = speed x mass. momentum is what makes an suv own a small car. But in this case, it'd probably wouldn't matter since the grain would go right through the body and thus little momentum would be absorbed.

The contributing factors to death would probably how the projectile would enter and exit the body and what body part hit.

If it went through like a needle, then I'd say it's unlikely there would be any death, even through the brain.

The acceleration (a) is due to the loss of speed when it hits you, not the gain of speed (zero) before. I have no way to know for sure, but given the very tiny surface area of a grain of sand, I doubt your body would decelerate it very much. With an average mass of say 10 mg for a grain of sand, it would take a deceleration of 10^5 m/s/s to exert 1 Newton on you.

makes sense.

 

[PlasmaBomb]

Originally posted by: darkxshade

Whether that's true or not. You'd have to consider how far that force is trailing the grain of sand because surely it's not moving at the speed of light. The grain would initially hit you first followed by the shear. But lets ignore that because the question is the initial blow from the grain itself and not what happens afterwards.

/facepalm

The force isn't trailing the grain of sand at all. A force is applied as soon as the grain of sand hits the skin. Granted it won't be at its maximum for a short period.

Several people have mentioned that going at that speed the grain of sand will have a lot of energy.

I don't think you quite realise how much.

Now assuming you don't pansy out and pick the smallest grain of sand you can find*...

say a grain around 1mm and weighing about 2.5 mg...

That grain of sand has the kinetic energy of about 270 tons of TNT (1.12 x 10^11).

Sure the grain will probably pass straight through you but it will impart some energy causing massive hydrostatic shock.

It will also behave like buck shot, as anything it hits (atoms) will get sent flying due to its massive inertia.

* even a weak ass grain of sand measuring 0.1mm and weighing squat, has about 10 tons TNTs worth of kinetic energy.

 

[Arkaign]

^^ PB, that's all well and good, but again, you're measuring the TOTAL kinetic potential, of which only a miniscule fraction could be transferring during an impact with a human. The very speed at which we are talking about precludes the sand being able to slow down and transfer the energy to a human target in any meaningful way.

The hydrostatic shock you speak of also requires enough resistance and deceleration to form. The combination of a tiny grain of sand with extreme speed makes that incredibly unlikely. The surface area of a grain of sand is almost insignificant compared to the surface area of even a .22 rifle round. Also to consider is that when even bullets hit humans travelling in speeds of 4,000FPS or less, there is a tremendously increased capacity to slow the round down and to begin transferring energy to the target. This very concept is utilized by the types of bullets such as hollowpoint, black talons, etc.

 

[dguy6789]

Originally posted by: PlasmaBomb

Originally posted by: darkxshade

Whether that's true or not. You'd have to consider how far that force is trailing the grain of sand because surely it's not moving at the speed of light. The grain would initially hit you first followed by the shear. But lets ignore that because the question is the initial blow from the grain itself and not what happens afterwards.

/facepalm

The force isn't trailing the grain of sand at all. A force is applied as soon as the grain of sand hits the skin. Granted it won't be at its maximum for a short period.

Several people have mentioned that going at that speed the grain of sand will have a lot of energy.

I don't think you quite realise how much.

So for comparison I will pick something pretty much everyone knows about...

Have you heard of Fat Man?

Do you know what its blast yield was?

21 kilotons of TNT - which can also be expressed in joules as - 88 Terajoules (8.78 x 10^13 joules).

Now assuming you don't pansy out and pick the smallest grain of sand you can find*...

say a grain around 1mm and weighing about 2.5 mg...

The kinetic energy of that grain of sand travelling at the speed of light makes FAT MAN look weak

Seriously.

That grain of sand has the kinetic energy of about 27 kilotons of TNT (1.12 x 10^14).

Sure the grain will probably pass straight through you but it will impart some energy causing massive hydrostatic shock.

It will also behave like buck shot, as anything it hits (atoms) will get sent flying due to its massive inertia.

* even a weak ass grain of sand measuring 0.1mm and weighing squat, has about 1 kiloton TNTs worth of kinetic energy.

:thumbsup:

 

[alkemyst]

Originally posted by: Arkaign

Originally posted by: SSSnail
So I googled and came up with the grain of salt will hit you with ~60 Newton. Whatever that means...

Correction : it will pass through you with almost all of that ~60 Newton intact.

Think of it like this :

a normal .357 round is much less deadly to a human than a black talon version of the same round, due to the bullet flattening out and fanning to distribute the kinetic energy to the target in the form of more damage.

A tiny grain of sand does not have the mass necessary to deliver a lot of energy to a non-dense target such as a human.

oooh black talon is that like a falcon punch?

 

[yhelothar]

Originally posted by: PlasmaBomb

Originally posted by: darkxshade

Whether that's true or not. You'd have to consider how far that force is trailing the grain of sand because surely it's not moving at the speed of light. The grain would initially hit you first followed by the shear. But lets ignore that because the question is the initial blow from the grain itself and not what happens afterwards.

/facepalm

The force isn't trailing the grain of sand at all. A force is applied as soon as the grain of sand hits the skin. Granted it won't be at its maximum for a short period.

Several people have mentioned that going at that speed the grain of sand will have a lot of energy.

I don't think you quite realise how much.

So for comparison I will pick something pretty much everyone knows about...

Have you heard of Fat Man?

Do you know what its blast yield was?

21 kilotons of TNT - which can also be expressed in joules as - 88 Terajoules (8.78 x 10^13 joules).

Now assuming you don't pansy out and pick the smallest grain of sand you can find*...

say a grain around 1mm and weighing about 2.5 mg...

The kinetic energy of that grain of sand travelling at the speed of light makes FAT MAN look weak

Seriously.

That grain of sand has the kinetic energy of about 27 kilotons of TNT (1.12 x 10^14).

Sure the grain will probably pass straight through you but it will impart some energy causing massive hydrostatic shock.

It will also behave like buck shot, as anything it hits (atoms) will get sent flying due to its massive inertia.

* even a weak ass grain of sand measuring 0.1mm and weighing squat, has about 1 kiloton TNTs worth of kinetic energy.

/thread

Yup, hydrostatic shock would be the domineering factor in this problem. And as explained in the link, the two factors contributing to hydrostatic shock is mass and velocity. That would mean hydrostatic shock would be inexplicably large in this problem, and thus organs would be shredded apart.

 

[hiromizu]

oh god. you guys are uber nerds that can't tell start trek from realty.

 

[JTsyo]

Originally posted by: mugs
Hmmmm... well, we take out tanks by hitting them with oversized lawn darts at about 3000 mph. I figure a grain of sand moving at the speed of light would have quite a lot of kinetic energy.

well that only works because the tanks have multiple inches of armor. If you were to fire the same round through a regular car it would cause almost no damage other than putting 2 holes in it. Spalling of the armor is what gets the crew.

EDIT: I mean through the car door or roof, not through the engine block or some heavy area.

The army was running into the same problem using armor-piercing rounds on unarmored targets. The shots would pass right through the targets and they would still be able to fight. Of course those guys were probably doped up.
Based on these examples, I think the grain would just pass through as long as it didn't hit anything hard and imparted some of its energy. As long as it was occurring in vacuum, I don't think there's enough time for any secondary thermal effects either.

I'm not a physicist but my understanding of the subject is that the object nearing lightspeed doesn't actually increase in mass but just acts like it does. For mass to increase either volume or density would have to increase both would take more matter to increase. Not sure what that would mean at the atomic level though.

 

[M0RPH]

Doh, for some reason I read "rice" instead of sand. If it's a grain of sand I don't think it would kill no matter where it hit.

 

[SlowSpyder]

I think a tremendous amount of energy would be transferred to you and it wouldn't be good. I'll assume this is done in a vacuum.

 

[yhelothar]

Originally posted by: SlowSpyder
I think a tremendous amount of energy would be transferred to you and it wouldn't be good. I'll assume this is done in a vacuum.

It wouldn't make a difference if it was done in a vacuum as hydrostatic shock only requires liquids to be present.

 

[Genx87]

By the laws of physics if the grain of sand was traveling at light wouldnt it have infinite mass? You'd probably vaporize from the energy that hit you.

 

[PlasmaBomb]

Originally posted by: phoenix79
(Assuming the OP meant 0.9999999...C)

You realise that that is the speed of light right?

 

[TuxDave]

Originally posted by: RESmonkey

Originally posted by: RESmonkey
I'm going to work this out using mechanics for an inelastic and elastic collision. BUT it's probably not going to be accurate since things moving at such speeds are not in the realm of Newtonian mechanics, but left for QFT, which I don't know, yet.

Ok this is probably wrong because I didn't take in account the make up of the human body, it's compression properties, etc. Just a simple physics thing:

Inelastic:

Mass of grain of sand -> 6.3E-7kg
mass of random human -> 75kg
speed -> (.999999999)(3E8 m/s)
(6.3E-7kg)(.999999999)(3E8) = ( 75kg + 6.3E-7kg)(vfinal)

vfinal -> 2.52 m/s

Elastic:

Dunno, depends?

The sand has a kinetic energy of about 94 Joules.

Can someone help me out here?

You forgot to include the sand's mass increase due to travelling at relativistic speeds.

 

[YOyoYOhowsDAjello]

Originally posted by: dainthomas

Originally posted by: YOyoYOhowsDAjello

Originally posted by: hiromizu

Originally posted by: YOyoYOhowsDAjello

Originally posted by: hiromizu

Originally posted by: isekii

Originally posted by: hiromizu
I think you guys are thinking way too scientifically to the point where you can't even get realistic answers. In reality, you'll feel a small pinch and the grain will bounce right off. Nothing more, nothing less.

If at all else i think it'll barely penetrate the skin and you should be able to just flick it off

I think you're pushing it there. A grain of sand won't penetrate your skin.

If a spec of paint traveling at 3.6km/sec can wreck a $50,000 window on the space shuttle, I would think that a grain of sand a some percentage of 300,000km/sec could penetrate your skin 😉

Yea but a space shuttle is flying at a few hundred miles per hour in space. In this case you're not moving and there's air n stuff to cause resistance. It's all relative.

If it's moving at a certain speed at the moment of impact, why does it matter if you're in a vacuum or not up until that point?

I believe the question was assumed to be in a vacuum since in an atmosphere you'd also have to deal with the effects of a shock wave. Most of these kinds of physics questions are assumed to be in a vacuum for simplification anyway.

hiromizu is saying that it's MORE dangerous in space than in atmosphere.

I certainly agree that there would be way more going on in an atmopheric scenario, none of which would make it less dangerous than in a vacuum.

He's thinking that the atmosphere would protect you from the particle moving at such velocity, but it's already given that it's moving at that speed when it actually hits you.

If there atmosphere were to protect us (and it certainly does), it would have to slow it down / burn it / etc. before it got to you at that speed. I'm asking how hiromizu thinks that the atmosphere is going to save him if it's already in contact with his body traveling at close to the speed of light.

 

[TruePaige]

The grain of sand would generate enough heat energy through its air resistance to rip itself apart.

Surprised no one said it, but unless I'm mistaken it should be right.


Also, perhaps you inherently negate this in the root of the hypothetical question but my first thought on reading the thread title was Terminal Velocity.

 

[Arkaign]

Originally posted by: alkemyst

Originally posted by: Arkaign

Originally posted by: SSSnail
So I googled and came up with the grain of salt will hit you with ~60 Newton. Whatever that means...

Correction : it will pass through you with almost all of that ~60 Newton intact.

Think of it like this :

a normal .357 round is much less deadly to a human than a black talon version of the same round, due to the bullet flattening out and fanning to distribute the kinetic energy to the target in the form of more damage.

A tiny grain of sand does not have the mass necessary to deliver a lot of energy to a non-dense target such as a human.

oooh black talon is that like a falcon punch?

lol 🙂

 

[Arkaign]

Originally posted by: JTsyo

Originally posted by: mugs
Hmmmm... well, we take out tanks by hitting them with oversized lawn darts at about 3000 mph. I figure a grain of sand moving at the speed of light would have quite a lot of kinetic energy.

well that only works because the tanks have multiple inches of armor. If you were to fire the same round through a regular car it would cause almost no damage other than putting 2 holes in it. Spalling of the armor is what gets the crew.

EDIT: I mean through the car door or roof, not through the engine block or some heavy area.

The army was running into the same problem using armor-piercing rounds on unarmored targets. The shots would pass right through the targets and they would still be able to fight. Of course those guys were probably doped up.
Based on these examples, I think the grain would just pass through as long as it didn't hit anything hard and imparted some of its energy. As long as it was occurring in vacuum, I don't think there's enough time for any secondary thermal effects either.

I'm not a physicist but my understanding of the subject is that the object nearing lightspeed doesn't actually increase in mass but just acts like it does. For mass to increase either volume or density would have to increase both would take more matter to increase. Not sure what that would mean at the atomic level though.

This is essentially correct.

Either by impact or hydrostatic shock, at the speeds we are talking about, there's simply no way the density of a human target would be enough to transfer a meaningful amount of energy, and thus, damage would be almost insignificant.

Fire the ~light speed sand grain at a 10-foot-diameter ball of lead, and you'd see a tremendously different reaction.

 

[olds]

I thought as an item reached light speed, it's mass increases "X" fold?

 

[Arkaign]

Originally posted by: oldsmoboat
I thought as an item reached light speed, it's mass increases "X" fold?

Mass does not = size, which is what would be dangerous in this regard.

If the grain of sand was traveling at near light speed, the ability of any part of it to influence a stationary human would be insignificant. Being exposed to a large gravity well for .000001th of a picosecond should be utterly irrelevant to the coherence of the non-dense tissue of a human.