DEFY McQUAID! #48 Smacking the Bullet

#48: Smacking the Bullet

The Question

Brandon, Kurt’s co-worker asks
I was wondering something. If a bullet were to be fired at a persons head from, let’s say, 40 meters away, is it possible to use your hand to alter the path of the bullet to miss your head? Pretend the person times it perfectly and strikes the bullet with their hand on the side of the bullet. Would this affect the path enough to miss, or what would happen? Thank you!

The Answer

So, you want to smack a bullet away, like it’s a mosquito. Interesting theory. Let’s do the math.

For this answer, I’m indebted to a party who shall remain nameless, who bolstered my flagging math skills and pointed the way to the answer.

Let’s do the variables first.

v = the velocity of the bullet. For our purposes, we are ignoring wind resistance and the effects of gravity.
t = the time it takes for the bullet to travel to your head.
d = the distance between your hand and your head.
F = the force applied by your hand to the bullet when you whack it.
m = the mass of the bullet.
a = the acceleration imparted by your hand to the bullet when you smack it.
h = half the width of your face. This is the distance you need to move the bullet so it doesn’t hit you.

Now for the equations.

t = d / v

The time it takes to travel a certain distance is the distance divided by the velocity.

F = m * a


a = dv/dt

Acceleration is the deravative of velocity with regards to time.


F = m * dv/dt

The slap will not affect the forward velocity; we are assuming
the strike is perfectly sideways.


F= m * dvy/dt j

Since the forward velocity only affects how hard the bullet has to be
hit, this can be rewritten as

F/m dt = dvy

We are assuming that the force applied is constant for a time duration, so we integrate.
The above equation, when integrated, yields:

F * t / m = vy

How to play with this vy piece?
This one requires a little more calculus than the last:

vy = dy/dt

h = (F*t^2)/(2*m)

Assembling and rearranging:

F = (2*h*m*vx^2) / (d^2)

Okay, we have a workable equation. Let’s fill in some estimated values.

h = 0.1m
d = 1m
m = 0.01kg
v = 1000m/s

F = 20,000 Newtons!

That’s a lot of force. It equates to approximately 4,000 pounds of force.

However, the average person’s fist, when swinging, delivers about 2,000 Newtons to their target. That’s 400 pounds of force.

So, in order to save your pretty face, you’d need to deliver a smack to the bullet that is 10 times more powerful than average, and that’s assuming you hit it directly on the side, and that your hand is impenetrable. Probably unlikely. What would really happen is that your hand would be damaged as well as your head. Not a pretty picture.

This is also not a pretty picture. Think about it.

14 thoughts on “DEFY McQUAID! #48 Smacking the Bullet

  • 12/6/2005 at 7:35 am

    not to mention your hand has to travel from the point it hit the bullet to your face at the speed the bullet is travelling while applying 4000 pounds of force to the bullet

  • 12/6/2005 at 10:06 am

    If you could react and move that fast, why not just duck?

  • 12/6/2005 at 10:39 am

    If you can react and move that fast and powerfully, why not showcase that power by smacking bullets out of the sky?

  • 12/6/2005 at 1:20 pm

    My initial guess was “no, it’d go through your f’ing hand and you’d die you fool”, and I was right! Guess that physics A-Level comes in handy for something at last.

  • 12/6/2005 at 5:02 pm

    2 things.

    As Shamus mentioned, your hand would have to move ridiculously fast. Inorder to not affect the forward velocity in any manner, the force would have to be instaneous. Seeing how this is virtually impossible with your hand, you would have to assume that there would be some form of friction betwen the palm of your hand and the bullet. While this frictional force is probably neglible, it would still be present.

    Second item, the Master Chief does this to a rocket in the first Halo novel, “the fall of reach”. But then again, he’s completely badass, so, we’ll believe that he could have done it successfully.

  • 12/6/2005 at 8:53 pm

    Did you just admit to reading a Halo novel? As if the starwars novels weren’t banal enough?

  • 12/6/2005 at 10:05 pm

    I will admit to reading and owning all three.

    I also own most of the SW novels, and have read about 3/4 of my collection so far.

  • 12/7/2005 at 8:18 am

    Good thing Brandon has a hand completly encassed in Unobtanium. I also watched him kick the crap out of 12 men at once. So this is totally feasible.

  • 12/7/2005 at 9:18 am

    I can’t help but point out that the same thing is achieved with a tea tray in the blockbuster summer feature “The Transporter”.

  • 12/7/2005 at 9:19 am

    Has anyone seen “The Transporter 2” this summer?

  • 12/7/2005 at 9:35 am

    Hey I was censored!!!!111
    Heh ;)

  • 12/7/2005 at 9:37 am

    1) Rockets are bigger and slower than bullets, though.
    2) But true, the MC is a badass.
    3) The first and 3rd Halo novels were decent, but the middle one was rubbish.

  • 12/7/2005 at 9:47 am

    I did. The only decent part about it was the V12 A8.

    It looked oh so sexy.

  • 12/7/2005 at 4:02 pm

    the best is the matrix when neo (keanu reeves) just puts his hand up and all the bullets stop and fall to the floor. Or what about when he folds so far back they fly over him..awesome. I might go and watch that film later.


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