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Episode 43 – Mythbusters’ Adam Savage


 

Adam Savage

We first met Adam Savage (from the Mythbusters) at The Amaz!ng Meeting 7 last summer, where he gave a talk about the creative process and failure that comes with ‘making’.  Of course, we knew that we had to get Adam on the show.  A few months later, we were lucky to talk with Adam about the Mythbusters, science education, and how he uses both experimentation and learning from mistakes in his work both on and off the show.

Links:

Direct download: LOL43.mp3

6 comments

  • Keith Hamlin

    No, they won’t… VF=VI+AT, where Velocity Final is the end speed, Velocity Initial is the start speed (probably anywhere from 400 to 1000 feet per second depending what ammo you are using) and AT is the Accelleration x Time factor (32 feet per second-per second over the time the bullet travels to ground.)
    Your bullet dropped would also not have the spin to keep it aerodynamic, and reach a terminal velocity of about 100 feet per second after 4 seconds, while in that time your firerd round could be buried in the soil, depending on your height.

    Can I come on to advise you in the maths and basics of physics? :)

  • Link Hyrule

    First, Keith has been misinformed. I don’t know of any conventional firearm (post-1900) that travels at a mere 400 feet per second. The lowest velocity I have ever heard of for a firearm was 700 fps for a low-velocity large caliber pistol. Furthermore 1000 fps is certainly not the limit for a firearm, as the M16 round travels at 3200 fps. Even if we are only considering pistols, this still ranges from 700 to over 2400 feet per second for normal pistols, with the average pistol hovering around 1000 feet per second.

    Second, Keith’s application of the formula Vf=Vi+AT is incorrect. When using this formula, the situation (meaning all the inserted variables and values) should be restricted to the axis on which the acceleration is acting. In this case, since the acceleration he is using is the vertical acceleration due to gravity, 32 feet/s/s, he should restrict all the other values he inserts to the vertical axis as well. This would mean that the Initial Velocity (vertical) would be 0, as the bullet does not start with a vertical velocity. Keith should fill in the other variables accordingly, in relation to their values on the vertical axis.

    On with the point:
    All objects on Earth are affected by the same force of gravity. This includes bullets. As such, because no conventional bullet produces any lift or other upward force, any two bullets will subsequently be affected equally by the same force of gravity.

    Let’s run through this scenario:
    1. The apparatus is set-up on a perfectly level plane, perpendicular to the pull of gravity. The theoretical shooting range is a sealed indoor room, eliminating wind.
    2. The gun (in this case we will use a benchrest sniper rifle due to the near-flawless accuracy, high tolerances, and remarkable resistance to outside forces) is precisely aimed perfectly parallel to the ground. The distance from the center of the barrel to the ground is set to the height at which the bullet will strike the ground at the 400 meter mark.
    3. The fired bullet is loaded in the chamber, also parallel to the ground, assuming the handloading manufacturing process is flawless. The bullets are small-caliber 4.6mm bullets of a high density, probably DU or Tungsten.
    4. The dropped bullet is set-up off to the side of the gun, in line with the chamber at the exact same height. It is set to drop at the instant the rear-end of the fired bullet exits the barrel. It is dropped such that the release is instantaneous and does not affect the dropped bullet in any way.
    5. We will assume that the manufacturing process is perfect, producing two identical and perfectly-weighted bullets, thus eliminating mid-air tumbling. Also assume that the dropped bullet stays parallel to the ground, not tumbling or rotating, reducing air-resistance.

    Now the test begins:
    6. The gun is fired (the striker hits the primer, igniting the gunpowder. The ignited gunpowder produces pressure within the shell, pushing the bullet out of the shell, into the barrel. With the bullet in the barrel, the still-expanding gasses behind the bullet continue to propel it faster and faster down the barrel. As the bullet is pushed down the barrel, it slides along the subtle twisting grooves in the barrel (the rifling), causing the bullet to spin on its axis at 4 rotations per meter traveled. The bullet leaves the barrel at 4000 fps (1219.2 m/s).)
    7. The dropped bullet begins to drop at the instant the rear-end of the fired bullet leaves the confines of the barrel.
    8. The lateral spin of the fired bullet, caused by the rifling of the barrel, imparts no special lift-creating or upward-moving properties to the bullet. The only thing the rotation of the bullet does (because it does not really spin very fast) is increase accuracy by helping the tip “cut” through the air. As such this doesn’t affect its resistance to falling.
    9. Because the rotation of the bullet provides no additional lift or upward motion, does not reduce the air resistance on the bottom of the bullet, and because its horizontal motion does not affect its vertical fall, it will approach the ground at the same speed as if it had no horizontal motion, right?
    10. By this reasoning, we can conclude that neither the velocity of the bullet nor its rotation affect the speed of its fall to Earth.
    11. Naturally, the dropped bullet has neither of these, which doesn’t make a difference as neither of these factors affects the vertical drop of the bullet.
    12. Now that we have established that the fired bullet has no flight-producing properties, fall-slowing properties, air-resistance-reducing properties, or fast-falling properties, we can conclude that the fired bullet experiences the same forces as the dropped bullet.
    13. Thus, since the fired bullet left the barrel (starting its fall) at the same time that the dropped bullet was released, with the same forces acting them, they both hit the ground at the same time.

    I am sorry if that was WAY too lengthy and WAY too wordy, I just wanted to be sure that I explained the situation to its fullest extent and with the greatest possible precision.

  • PhysicsHertzGood

    The explanation of the correction is right on and I am here to second his statement. You can’t mix up what you are talking about with acceleration and velocity. I feel pretty confident with what the mythbusters did. I don’t think there was a way they could have been that close without being correct.
    However, it is always good to analyze things you don’t have a full understanding of. I think that from this, you can realize your mistake and forever you will know this law of projectile motion. I personally would like to see the mythbusters test the Big Bang Theory. (Please observe the previous sentence as a joke.)

  • Eric R.

    Link Hyrule, thank you for you lenghty detailed description of why the bulletes would strike the ground at the same time, however, in line 13, you gave the reason that both would NOT hit the ground simultaneously. You do have the same force (gravity) acting on both object, but on the bullet fired form the gun, gravity isn’t the only force applied to the object. The inertia provided by the gunpowder is stronger than the force of gravity for a small period of time after the bullet leaves the barrel. The farther the bullet travels and longer it is in the air, the more gravity will take effect on it. Eventually the horizontal velocity will slow down enuff for gravity to take over, but for the first second or two, the bullet is traveling damn near horizontally, which would keep it in the air longer.

  • Ricky

    @Eric R – Your statement that the horizontal velocity would impact the effect that gravity has on an object is untrue. This would only be true if the object itself had any capacity to generate lift, which is the only force that can resist the pull of gravity on an object moving horizontally. Since the fired bullet has zero lift, gravity affects it in the same way as the dropped bullet, regardless of horizontal velocity.

  • Collin

    I agree with line of thinking that bullets have no special lift creating or upward moving properties. Therefore flying horizontally until gravity causes a gradual but progressive vertical drop.A lot of people disagree by saying that bullets do rise above a horizontal plane creating an arc effect. Which theory is correct and where can I find facts?
    I

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