The Physics Of Flintstones-Style Braking

Edward Niedermeyer
by Edward Niedermeyer

This is the kind of video that might suffice as standalone weekend entertainment. After all, braking a truck with your feet is a pretty demonstrably bad idea. But the lovable nerds at Popular Science just had to take it a step further and work out the physics of trying to halt a truck ala Fred Flintstone, noting

Let’s estimate he can push down with a force about a quarter of his weight. If he weighs 200 pounds, this would result in a force of 50 pounds, or 225 N. We also know that the force of friction (F) between his feet and the asphalt depends on the force with which he pushes down (N) and the “coefficient of kinetic friction”(μ) between the soles of his shoes, which we will assume are made of rubber, and the pavement.

F = μN

The μ between rubber and asphalt varies between 0.5 and 0.8. Let’s assume a value of 0.7. Therefore, solving for stopping distance, we get:

D = ½(2100kg)(18m/s)2/(0.7)(225N) = 2160 meters, or over 1.3 miles!

The situation might be improved if he exerted his full 200 pounds, or 900 Newtons, of force against the ground. In that case:

D = 1/2(2100kg)(18m/s)2/(0.7)(900N) = 540 meters (about a third of a mile)

However, the amount of torque exerted on his ankles and knees might make that a problematic proposition.

Surf on over to PopSci for the entire breakdown (no pun intended).

Edward Niedermeyer
Edward Niedermeyer

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9 of 19 comments
  • Zackman Zackman on Aug 27, 2011

    How this knucklehead avoided hitting anyone is beside me. If he was smart, the truck, as beat up as it appeared to be, should have a hole rusted through the floor and he could've used BOTH feet. If he did that, he would've stopped, no problem. Must've been Barney and not Fred!

    • IDANECK IDANECK on Aug 27, 2011

      Looked like he hit at least 3 vehicles...Murano, Monte, and car in the turn lane of second intersection.

  • Rada Rada on Aug 28, 2011

    Reminds me of another physics problems - what must the velocity of a human body be, in order to completely evaporate upon ideally inelastic impact with a wall that, for simplicity, has zero specific heat? The answer is a surprisingly attainable velocity.

    • See 2 previous
    • Zackman Zackman on Aug 28, 2011

      @Zackman That's what I thought!

  • Robert.Walter Robert.Walter on Aug 28, 2011

    I'm surprised his feet didn't catch some kind of crack or joint in the pavement and get snapped off. What an incredibly stupid person and a real danger to society. With that lack of judgement, he needs to lose his license.

    • Mazder3 Mazder3 on Aug 28, 2011

      I think some kind of crack or joint is why he tried stopping with his feet.

  • Sinistermisterman Sinistermisterman on Aug 28, 2011

    I only ever lost my brakes once when a rear brake cylinder blew on crappy old K car. I managed to creep home avoiding going down hill, using low gears, the parking brake and occasionally jamming it into reverse when I REALLY had to stop. This guy is a tool.