I have a physics question...

[tranceport]

What would happen to a human if they were hit by a proton traveling at the speed of light

Say for instance they were standing in a particle accelerator and got hit by 1 single proton traveling at the speed of light. Center mass.


What would happen to a human?

 

[CycloWizard]

What's the mass of a proton? I'm too far removed from frosh chemistry to recalll.

 

[Gibsons]

Originally posted by: CycloWizard
What's the mass of a proton? I'm too far removed from frosh chemistry to recalll.

Mass of proton : 1,6726 x 10^(-27) kg
Mass of neutron: 1,6749 x 10^(-27) kg
Mass of electron: 0,00091x10^(-27) kg

from link

 

[CycloWizard]

Originally posted by: Gibsons
Mass of proton : 1,6726 x 10^(-27) kg
Mass of neutron: 1,6749 x 10^(-27) kg
Mass of electron: 0,00091x10^(-27) kg

from link

Thanks... Now comes a question I had yesterday but forgot to post on here: if these sub-atomic particles are travelling at or near light speed (as I believe electrons tend to do), why do they have finite mass?

Using the classic kinetic energy formula E=1/2*mass*velocity^2, the energy of the proton would be 7.52x10^-11 J, which would mean pretty much nothing would happen. Since we're talking about the proton at the speed of light, the classical equation does not hold:
linky

Using the graph to the left determine the kinetic energy of a proton moving at 98% the speed of light. Express your answer in MeV.
About 2x1011eV = 2x105MeV. Point out to students that at this velocity classical physics begins to break down, and the relativistic mass of the proton becomes important.

 

[aplefka]

This is just a pretty basic guess, but wouldn't it be just as if a very small pellet from a pellet gun had hit the human? I'm sure it's more technical than that but am I on the right track?

Obviously there would be a much smaller entry hole and in addition to that there would be an exit hole as well, since nothing at that speed could be stopped by anything inside of our bodies. I'm assuming it would be a fatal blow and a very slow and painful death, because wouldn't your body just leak (for lack of a better word)?

 

[Gibsons]

Originally posted by: aplefka
This is just a pretty basic guess, but wouldn't it be just as if a very small pellet from a pellet gun had hit the human? I'm sure it's more technical than that but am I on the right track?

Obviously there would be a much smaller entry hole and in addition to that there would be an exit hole as well, since nothing at that speed could be stopped by anything inside of our bodies. I'm assuming it would be a fatal blow and a very slow and painful death, because wouldn't your body just leak (for lack of a better word)?

No it wouldn't behave like a bullet. As soon as it interacted with some matter there would be a release of energy, basically an explosion.

so just to calculate basic kinetic energy

a .30 cal bullet is 100g at 800m/s so... 0.5mv^2 is 32x10^6

a proton is 1.6726 x 10^(-24) g at 299,792,458m/s (speed of light in a vacuum) so 7.5x10^-8

so by simple kinetic energy it's got negligible energy compared to a bullet. If you use e=mc^2 instead of 1/2mv^2 it doesn't seem to change much.

disclaimer: I didn't double check any of my math!

 

[tranceport]

So I would live?

Would I feel it?

Would there be any visable indication I was hit?

 

[TuxDave]

Originally posted by: Gibsons

Originally posted by: aplefka
This is just a pretty basic guess, but wouldn't it be just as if a very small pellet from a pellet gun had hit the human? I'm sure it's more technical than that but am I on the right track?

Obviously there would be a much smaller entry hole and in addition to that there would be an exit hole as well, since nothing at that speed could be stopped by anything inside of our bodies. I'm assuming it would be a fatal blow and a very slow and painful death, because wouldn't your body just leak (for lack of a better word)?

No it wouldn't behave like a bullet. As soon as it interacted with some matter there would be a release of energy, basically an explosion.

so just to calculate basic kinetic energy

a .30 cal bullet is 100g at 800m/s so... 0.5mv^2 is 32x10^6

a proton is 1.6726 x 10^(-24) g at 299,792,458m/s (speed of light in a vacuum) so 7.5x10^-8

so by simple kinetic energy it's got negligible energy compared to a bullet. If you use e=mc^2 instead of 1/2mv^2 it doesn't seem to change much.

disclaimer: I didn't double check any of my math!

You forgot to include that if the proton was indeed moving at the speed of light, its mass would have been infinite.

 

[kobymu]

you are bombarded with subatomical particle (manly photons) 24/7.

however atomic particle (proton, neutron and electron) are a completely different story. a single electron (at the speed of light) will probably wont do a thing to a human body but a proton or a neutron do have more mass so i really dont know, although i dont believe a single proton or neutron (considering the mass gain) will cause such a dramatic effect.

/edit
every time you are near a strong electromagnetic field (near a grid power line) you are bombarded by electrons (not that many but definitely more than one) at a speed which is close to the speed of light...

 

[Velk]

Originally posted by: tranceport
What would happen to a human if they were hit by a proton traveling at the speed of light

Say for instance they were standing in a particle accelerator and got hit by 1 single proton traveling at the speed of light. Center mass.


What would happen to a human?

Depends if the proton hits something or not. People aren't particularly solid at a subatomic level.

If it did hit something - no idea.

8)

 

[tranceport]

Originally posted by: Velk

Originally posted by: tranceport
What would happen to a human if they were hit by a proton traveling at the speed of light

Say for instance they were standing in a particle accelerator and got hit by 1 single proton traveling at the speed of light. Center mass.


What would happen to a human?

Depends if the proton hits something or not. People aren't particularly solid at a subatomic level.

If it did hit something - no idea.

8)

assume it hits a proton in one of my atoms.

 

[Calin]

It might create (well, transmute) the atom it hits into another kind of atom. The impulse or energy of the proton have little signifiance compared to a human body. It might be possible to change an carbon to an nytrogen, or an nytrogen to an oxygen. Nothing really important.
However, at light speed the proton would have infinite mass and infinite energy. However, in case of impact, it will leave behind it a trail of destruction less than a micron wide. Good luck living with such a terrible wound.

 

[Calin]

The killing effect of the neutron bombs would be related to the very fact that our body's cells are created based on the DNA spiral. Any damage in a big enough part of the DNA spirals in the body will have a "snowball" effect (they tend to become less and less similar to the original DNA). This explains why victims of nuclear accidents need continous transplants of blood/skin/...
EDIT: I might be wrong, but my assumption would be the "critical" dose is some kind of trillions of neutrons or more. More probably more than less

 

[Gibsons]

Originally posted by: TuxDave

Originally posted by: Gibsons

Originally posted by: aplefka
This is just a pretty basic guess, but wouldn't it be just as if a very small pellet from a pellet gun had hit the human? I'm sure it's more technical than that but am I on the right track?

Obviously there would be a much smaller entry hole and in addition to that there would be an exit hole as well, since nothing at that speed could be stopped by anything inside of our bodies. I'm assuming it would be a fatal blow and a very slow and painful death, because wouldn't your body just leak (for lack of a better word)?

No it wouldn't behave like a bullet. As soon as it interacted with some matter there would be a release of energy, basically an explosion.

so just to calculate basic kinetic energy

a .30 cal bullet is 100g at 800m/s so... 0.5mv^2 is 32x10^6

a proton is 1.6726 x 10^(-24) g at 299,792,458m/s (speed of light in a vacuum) so 7.5x10^-8

so by simple kinetic energy it's got negligible energy compared to a bullet. If you use e=mc^2 instead of 1/2mv^2 it doesn't seem to change much.

disclaimer: I didn't double check any of my math!

You forgot to include that if the proton was indeed moving at the speed of light, its mass would have been infinite.

True, but my calculator doesn't have an infinity button.

 

[f95toli]

If a a single proton traveling at 99% of the speed of light hit you not much would happen. However, if you work in an enviroment where you are subjected to high-doses of high-energy particles (muons, positrons, electrons etc) on a daily basis the risk of cancer increases somewhat.
This is true for e.g. pilots and other people working on commerical airliners.

 

[CycloWizard]

Originally posted by: TuxDave
You forgot to include that if the proton was indeed moving at the speed of light, its mass would have been infinite.

I was going to post this a couple days ago but forgot. Since electrons are almost always moving near or at the speed of light (IIRC), why is their mass finite/infinitesimal?

Originally posted by: Gibsons
True, but my calculator doesn't have an infinity button.

Bah! Upgrade to a TI-89.

 

[nwfsnake]

Spontaneous Combustion! :Q

 

[icarus4586]

What would happen to a human if they were hit by a proton traveling at the speed of light

Say for instance they were standing in a particle accelerator and got hit by 1 single proton traveling at the speed of light. Center mass.


What would happen to a human?

Since it's impossible to make a particle that has mass go the speed of light, the universe would break.

I was going to post this a couple days ago but forgot. Since electrons are almost always moving near or at the speed of light (IIRC), why is their mass finite/infinitesimal?

The mass of an object moving at speeds close to the speed of light is defined by:
(mass at speed near c) = (rest mass) / sqrt(1- (v^2)/(c^2))

So, for an proton with rest mass 1.6726*10^-24 g, traveling at 99% the speed of light, mass = 1.1857*10^-23 g

 

[silverpig]

Originally posted by: f95toli
If a a single proton traveling at 99% of the speed of light hit you not much would happen. However, if you work in an enviroment where you are subjected to high-doses of high-energy particles (muons, positrons, electrons etc) on a daily basis the risk of cancer increases somewhat.
This is true for e.g. pilots and other people working on commerical airliners.

Pretty much right here.

We are hit with cosmic ray muons constantly (a few per second at least), and nothing happens to us. The mass of the muon is smaller than that of a proton, but not insignificantly so. There are small quantities of radioactive elements present everywhere that are constantly decaying and spitting out neutrons, alpha particles (2 protons and 2 neutrons), electrons, and gamma rays (photons). We are hit by these constantly. Nothing much happens.

There are trillions of neutrinos passing through your body every second. They are very very weakly interacting though and virtually all of them pass through completely untouched.

 

[The Boston Dangler]

Originally posted by: tranceport
So I would live?

Would I feel it?

Would there be any visable indication I was hit?

Do you have reason to believe you have been struck by a proton? Grassy knoll?

Seriously, probably nothing.

Worst case scenario #1: The proton strikes some DNA, altering the genes, you now have cancer. This is what happens when 1 plutonium atom is trapped in the lungs.

Worst case scenario #2: The impact results in a massive release of enegry, like a microscopic firecracker. Hope it's not a head shot.

 

[cquark]

Originally posted by: CycloWizard

Originally posted by: TuxDave
You forgot to include that if the proton was indeed moving at the speed of light, its mass would have been infinite.

I was going to post this a couple days ago but forgot. Since electrons are almost always moving near or at the speed of light (IIRC), why is their mass finite/infinitesimal?

Mass doesn't increase with velocity.

Mass is the magnitude of the energy-momentum four-vector and as such isn't altered by frame changes. The so-called relativistic mass, which was invented to make popular explanations of special relativity simpler though less accurate, is actually the time component of that four-vector. It is frame dependent, but it cannot be used in place of mass in most equations. Perhaps Einstein said it best:

"It is not good to introduce the concept of the mass M = m/(1-v2/c2)^1/2 of a body for which no clear definition can be given. It is better to introduce no other mass than `the rest mass' m. Instead of introducing M, it is better to mention the expression for the momentum and energy of a body in motion."

We can calculate the energy of a near light-speed proton as follows though

E = m c^2 ( 1/sqrt(1 - v^2/c^2) - 1 )

If v = 0.999999c, then the factor is parentheses is about 100, indicating the proton has a kinetic energy 100X that of its rest mass energy or only 1.6726 x 10^(-24)g worth of energy.

If v = 0.99999999c, then the factor in parentheses is about 1000. For about every two nines, you gain an order of magnitude in energy, so you're going to need about 54 9's after the decimal point to have about a gram's worth of kinetic energy in a proton.

 

[CycloWizard]

Originally posted by: cquark
Mass doesn't increase with velocity.

Mass is the magnitude of the energy-momentum four-vector and as such isn't altered by frame changes. The so-called relativistic mass, which was invented to make popular explanations of special relativity simpler though less accurate, is actually the time component of that four-vector. It is frame dependent, but it cannot be used in place of mass in most equations. Perhaps Einstein said it best:

"It is not good to introduce the concept of the mass M = m/(1-v2/c2)^1/2 of a body for which no clear definition can be given. It is better to introduce no other mass than `the rest mass' m. Instead of introducing M, it is better to mention the expression for the momentum and energy of a body in motion."

Ah, that makes sense now. I never considered frame invariance in this sense. I actually read Einstein's simplified book on general and special relativity, though I never actually 'learned' about it in school or anything, so I have more vague ideas than concrete notions.

 

[AsiLuc]

First of all, the proton can not travel with the speed of light.
It can get close, but it can't reach c.
Furthermore, I side with cquark, he knows what he's talking albout. So: mass does not increase. It's actually the only thing independent of the relative speed of the observer. The result depends on the energy of the proton. With enough energy, you'll be blown away, like a car hits you. But particles with such energy are not created. You'll probably won't notice a thing. A big dosis might get you cancer though.

 

[Geniere]

A proton at near light speed will pass through the human body without effect. Protons are used in cancer treatment but the velocity of the proton is about 60% of the speed of light. The energy of the accelerator is adjusted to compensate for the distance the tumor is from the skin surface.

While the proton is moving through the body it loses kinetic energy (velocity) via various scattering events until the ?Bragg Peak? point is reached. At that point all the remaining energy is released. Since this point is well defined, it minimizes damage to healthy tissue and maximizes damage to the treatment area. The Bragg Peak point would not be reached unless the patient was the size of several elephants if the incident proton was at 0.99C.

To fight cancer, humans are purposely and routinely bombarded with gamma rays, x-rays, electrons, neutrons, positrons, protons? Except for the large cancer treatment hospitals, most hospitals use photon and electron therapy devices. The disadvantage is the treated volume is not well defined and surrounding healthy tissue can be damaged. In practice, damage to the healthy tissue is avoided by many small doses delivered at different angles (machine rotates) so most of the dose is at the focal point.