What happens if you hit a bullet from the side?

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Discussion Overview

The discussion centers around the theoretical scenario of a person attempting to hit a bullet from the side with their hand. Participants explore the implications of such an interaction, considering aspects of collision dynamics, potential injuries, and the physics of momentum transfer. The conversation includes both conceptual and technical reasoning about the nature of the collision and its effects on the hand and bullet.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that if a hand were to move at the same speed as the bullet, it could theoretically change the bullet's direction without harming the hand.
  • Others argue that the collision would likely be inelastic, with significant momentum exchange, and that the bullet could cause considerable damage to the hand regardless of the angle of contact.
  • There are claims that the bullet could graze the hand, potentially causing tissue damage due to heat from friction, but not permanent injury.
  • Some participants suggest that a frictionless bullet would not harm the hand, while others question the validity of this assumption in a real-world scenario.
  • Several participants emphasize that the speed of the bullet (e.g., 1700 mph) would result in severe injury to the hand, regardless of the angle or speed of the hand.
  • There is a discussion about the nature of the collision, with some suggesting that the hand's softness compared to the bullet's rigidity would lead to injury.
  • Some participants express skepticism about the feasibility of the scenario, noting that human movement speeds are significantly lower than bullet speeds.

Areas of Agreement / Disagreement

Participants generally disagree on the outcomes of the scenario, with multiple competing views on the effects of the collision, the nature of the forces involved, and the potential for injury. There is no consensus on whether the hand could be unharmed or how the bullet's trajectory would be affected.

Contextual Notes

Discussions include assumptions about the elasticity of the hand and bullet, the effects of friction, and the specific angles of impact. The scenario is highly theoretical and relies on idealized conditions that may not reflect real-world physics.

TheShredder
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My brother actually said this and felt that it would not effect the person's hand. He said, theoretically, if a person were to move their hand from the side of the bullet (so as to slap the bullet) , at the same speed as the bullet, the bullet would would change its direction and the hand would be left unharmed. I feel that the bullet would graze the person's hand, while it is in contact with the bullet, also the speed of the hand does not need to be at the same speed as the bullet to cause it to change direction, it would require a certain amount but not exactly the same as the bullet.
Which one is right and why?
also here is a picture I made in case I could not explain the problem properly: http://imgur.com/ceATo5d
Thank you!
 
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You have a collision between two objects. Is it elastic, or inelastic?
 
I guess this collision would be elastic since a hand is a soft object.
Either way though there will be some exchange of momentum.
The moving hand may very slightly alter the trajectory of the bullet,
however the much faster moving bullet could apply a very considerable force to a part of the hand which it touches, and very possibly this could result in grazing or worse damage depending on factors such as the exact angle of contact
 
rootone said:
I guess this collision would be elastic since a hand is a soft object.
Either way though there will be some exchange of momentum.
The moving hand may very slightly alter the trajectory of the bullet,
however the much faster moving bullet could apply a very considerable force to a part of the hand which it touches, and very possibly this could result in grazing or worse damage depending on factors such as the exact angle of contact

If the hit is made at a 90o angle
 
Probably would result in a nasty graze along with some tissue damage due to heat caused by friction, but no permanent injury.
The trajectory of the bullet would probably be altered by a very small amount.
 
rootone said:
Probably would result in a nasty graze along with some tissue damage due to heat caused by friction, but no permanent injury.
The trajectory of the bullet would probably be altered by a very small amount.
That is my expectation as well. A frictionless cold bullet would not harm the hand (assuming it is completely flat to make that collision exactly as described).
 
1889_20_280-gunshot-wound-hand.jpg

Bullet grazing wounds to the palm and wrist.
 
mfb said:
That is my expectation as well. A frictionless cold bullet would not harm the hand (assuming it is completely flat to make that collision exactly as described).
I realize you're trying to make an ideal scenario here, to isolate the mechanisms, but I'm not sure that discounting friction illuminates the issue here. Of course a frictionless bullet would do no harm.
 
If you were to hit the bullet and cause the exact force of the bullet it would change direction with no effect. But if the force of the object hitting it was less then the force measured with the speed of the bullet it would cause damage. Also this all depends on the angle of hitting the bullet and the direction it was hit. To the side up or down gravity does play effect in this equation
 
  • #10
Alasmic said:
If you were to hit the bullet and cause the exact force of the bullet it would change direction with no effect. But if the force of the object hitting it was less then the force measured with the speed of the bullet it would cause damage.
I refute both these claims.

We're talking about a human hand here. Damage can and probably will occur regardless of whether the oblique force is equal, less than or greater than the momentum of the bullet.
 
  • #11
DaveC426913 said:
I refute both these claims.

We're talking about a human hand here. Damage can and probably will occur regardless of whether the oblique force is equal, less than or greater than the momentum of the bullet.
If your talking about heat yes but for the amount of time touching the bullet there would not be enough time to transfer the heat needed to cause damage
 
  • #12
Alasmic said:
If your talking about heat yes but for the amount of time touching the bullet there would not be enough time to transfer the heat needed to cause damage
Regardless of skin blood bone or metal if the force is exact then their shouldn't be variants
 
  • #13
TheShredder said:
at the same speed as the bullet

A bullet moves at 1000 mph. People don't move that fast.
 
  • #14
Vanadium 50 said:
A bullet moves at 1000 mph. People don't move that fast.
His question was theoretical
 
  • #15
TheShredder said:
also here is a picture I made in case I could not explain the problem properly: http://imgur.com/ceATo5d
Thank you!

TheShredder said:
If the hit is made at a 90o angle

This won't work. You have a 1700 mph bullet and 1700 mph hand. They have a collision velocity of 1700*sqrt(2) = 2400 miles per hour. The bullet puts a hole in the hand no matter how cold or frictionless it is.
 
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  • #16
Alasmic said:
If your talking about heat yes but for the amount of time touching the bullet there would not be enough time to transfer the heat needed to cause damage
I can say that I have 'experimental evidence' that a very brief contact of human flesh with a hot object (such as a soldering iron) will cause tissue damage.
 
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  • #17
stedwards said:
1700 mph bullet and 1700 mph hand. They have collision velocity of 1700*sqrt(2)
That was my take on the OP as written. The other possible "twist" is that "The Bulletproof Monk" can parallel the trajectory for a couple milliseconds and "tap/slap/nudge" it sideways by some measureable amount.
 
  • #18
stedwards said:
This won't work. You have a 1700 mph bullet and 1700 mph hand. They have a collision velocity of 1700*sqrt(2) = 2400 miles per hour. The bullet puts a hole in the hand no matter how cold or frictionless it is.
At a 90 degree angle it would knock the bullet of its course but at and degree above that I believe yes it would go through the skin probably at twice the speed of a stationary hand
 
  • #19
Bystander said:
That was my take on the OP as written. The other possible "twist" is that "The Bulletproof Monk" can parallel the trajectory for a couple milliseconds and "tap/slap/nudge" it sideways by some measureable amount.

Alasmic said:
At a 90 degree angle it would knock the bullet of its course but at and degree above that I believe yes it would go through the skin probably at twice the speed of a stationary hand

No. In the center of velocity frame you just get hit by a faster bullet. Bystander understands what trajectory is required of the magical 1700+ mph hand.
 
  • #20
stedwards said:
No. In the center of velocity frame you just get hit by a faster bullet. Bystander understands what trajectory is required of the magical 1700+ mph hand.
Do you propose constructing a lab with the object of impact having the same elasticity and angle!?
 
  • #21
No. Why?
 
  • #22
Considering your hand is very squishy compared to a perfectly rigid object, hitting the bullet with enough force to push it off target would undoubtedly cause the bullet to go through a considerable amount of skin/muscle, not just skim along the surface.
 
  • #23
TheShredder said:
if a person were to move their hand from the side of the bullet (so as to slap the bullet) , at the same speed as the bullet,
Maybe he meant hitting from the back, moving the hand slightly faster than the bullet?
 
  • #24
Alasmic said:
Regardless of skin blood bone or metal if the force is exact then their shouldn't be variants
How do you come to the conclusion that somebody's hand would not be severely damaged by impact with a bullet moving at 3 times the speed of sound? The fact that the hand is moving obliquely will not change the momentum of the bullet. Trying to swing at it hard enough to deflect it is going to tear your hand up.
 
  • #25
DaveC426913 said:
The fact that the hand is moving obliquely will not change the momentum of the bullet.

Effectively, the momentum is increased.

This little question is similar to asking if you can be saved from getting smashed into the floor of a falling elevator if you jump at the moment before impact.

What is not so obvious in the frame of the building, is obvious in the elevator frame.
What is not so obvious in the Earth frame, is obvious in frame of the hand.
 

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