Can a bullet knock someone back as hard as a semi truck?

In summary: However, the fastball is spread out over a much greater time interval. In summary, the conversation touched on the topic of whether a bullet could knock someone back with the same force as being hit by a semi truck. It was discussed that this is a common movie physics mistake and that in reality, the recoil spring is what gives bullets like hydroshock their knockdown power. The difference between knockdown and knock back was also explained. The conversation then shifted to the topic of novices being knocked over by a shotgun, which was attributed to their flinching from the loud noise rather than the actual force of the shot. The conversation ended with a humorous comment about finding the situation funny in real life.
  • #1
jeremyearle5
1
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A friends father told him that a hydroshock bullet (a type of hollowpoint bullet that spreads out on impact and ussually doesn't exit the target) shot into a mans palm from ten feet away would impart a force on the rest of his body equal to being hit by a semi truck. I know this is ridiculous, but it got us to talking about Newton's 3rd law and whether or not a bullet could ever knock someone back. In order for a bullet to knock someone back wouldn't it also have to knock the shooter back an equal amount? I guess I'm just asking for someone to give me a good physics overview of this whole scenario, please.
 
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  • #3
jeremyearle5 said:
A friends father told him that a hydroshock bullet (a type of hollowpoint bullet that spreads out on impact and ussually doesn't exit the target) shot into a mans palm from ten feet away would impart a force on the rest of his body equal to being hit by a semi truck. I know this is ridiculous, but it got us to talking about Newton's 3rd law and whether or not a bullet could ever knock someone back. In order for a bullet to knock someone back wouldn't it also have to knock the shooter back an equal amount? I guess I'm just asking for someone to give me a good physics overview of this whole scenario, please.

A common demostration in boot camp long, long ago (back about the time water was invented) was for a drill sergeant to hold an M1 rifle with the butt resting on his nose (sometimes other parts of the anatomy) and fire it. The secret, of course, was the recoil spring. The reverse of the same principle gives bullets like the hydroshock a tremendous knockdown power because the bullet decelerates so quickly. But, knockdown is not the same as knock back.
 
  • #4
mgb_phys said:
You are exactly correct - the target flying backwards is a typical movie-physics error.
See http://www.intuitor.com/moviephysics/mpmain.html#glass for this and other movie physics fun.

I have heard of many novices knocked over by firing a shotgun. Your article was quite edifying as to the differences of energy, momentum and force involved.
 
  • #5
That's because they stand leaning backwards like they were holding a camera and fall over when they hear the load bang!
 
  • #6
mgb_phys said:
That's because they stand leaning backwards like they were holding a camera and fall over when they hear the load bang!

I have no idea why i found that funny irl ^^
 
  • #7
Loren Booda said:
I have heard of many novices knocked over by firing a shotgun. Your article was quite edifying as to the differences of energy, momentum and force involved.

I've seen people knocked over, but I think they were flinching from the expected "BANG". A typical shotgun has a "kick" of 20-30 ft-lb. By way of comparison, a major league fastball has an energy of about 150 ft-lb.
 

Related to Can a bullet knock someone back as hard as a semi truck?

What is the 3rd law of motion?

The 3rd law of motion, also known as Newton's third law, states that for every action, there is an equal and opposite reaction. This means that when an object exerts a force on another object, the second object will exert a force back on the first object that is equal in magnitude and opposite in direction.

How does the 3rd law apply to bullet impact?

The 3rd law applies to bullet impact by explaining the forces involved in the collision between the bullet and its target. When the bullet is fired from a gun, it exerts a forward force on the gun, causing it to recoil. At the same time, the bullet exerts an equal and opposite force on the target, causing it to move in the opposite direction. This is what causes the bullet to penetrate and potentially damage the target.

What factors affect the impact of a bullet?

The impact of a bullet can be affected by various factors, including the speed and mass of the bullet, the shape and composition of the bullet, the angle at which it hits the target, and the density and thickness of the target material. These factors can all affect the amount of force exerted by the bullet and the resulting damage to the target.

Can the 3rd law of motion be used to determine the impact of a bullet?

Yes, the 3rd law of motion can be used to determine the impact of a bullet by considering the forces involved in the collision between the bullet and its target. By measuring the velocity and mass of the bullet, as well as the density and thickness of the target material, scientists can calculate the amount of force exerted by the bullet and predict the resulting impact and damage.

How can the 3rd law of motion be applied to improve bullet impact?

The 3rd law of motion can be applied to improve bullet impact by understanding the forces involved and designing bullets and firearms that can maximize the transfer of energy to the target. This can lead to more effective and efficient bullets that can achieve the desired impact while minimizing the amount of recoil and potential damage to the firearm.

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