4 ms·

Why is the math wrong if this is a "traffic engineer"? > A quick physics lesson: The force of impact from a car increases quadratically with speed. This means

Why is the math wrong if this is a "traffic engineer"? > A quick physics lesson: The force of impact from a car increases quadratically with speed. This means that doubling the speed quadruples the force of the impact. That is absolutely not what quadratically means.

PhasmaFelis 9y ago
It's not? I'm not a mathematician, but Wikipedia says "In mathematics, a function or sequence is said to exhibit quadratic growth when its values are proportional to the square of the function argument or sequence position."
- GalacticDomin8r 9y ago
  That's my point. The wiki definition you have cited is correct, but it doesn't compute with the article.
  - DannyBee 9y ago
    I'll save everyone else the trouble. The original data is from https://www.aaafoundation.org/sites/default/files/2011PedestrianRiskVsSpeed.pdf https://www.aaafoundation.org/sites/default/files/2011Pedest... If you look, on page 9, you can see the plots of impact speed vs risk of death. They are clearly non-linear, and they you can also read that they tried various fitting methods for missing data (and quadratic best fit things). I'm just guessing that you are confused because it does not appear the constant for the x^2 term is >1.
    - GalacticDomin8r 9y ago
      I'll make it even easier: http://hyperphysics.phy-astr.gsu.edu/hbase/impcal.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/impcal.html#c1
    - scotty79 9y ago
      Quadratic relationship is between the speed and force of impact. If you want to accelerate pedestrian to certain speed you have to pump kinetic energy into him. You do that by applying a force over some distance (distance is how much pedestrian will squish during impact before it starts moving with the car) so to acellerate to double speed, you need to pump in quadruple energy, you need to quadruple the force since squishing distance is the same (until you reach speeds that pulverize pedestrian bones).
  - scotty79 9y ago
    f(x)=a*x^2 f(2*x)=a*(2*x)^2=a*4*x^2=4*a*x^2=4*f(x) Doubling the argument quadruples the value of quadratic function.
    - GalacticDomin8r 9y ago
      Try again using order of operations. It does not expand to (2*x)^2, it is simply 2x^2. To say it another way: 4x^2 != 2x^2
cozzyd 9y ago
2^2 = 4?

PhasmaFelis 9y ago

It's not? I'm not a mathematician, but Wikipedia says "In mathematics, a function or sequence is said to exhibit quadratic growth when its values are proportional to the square of the function argument or sequence position."

GalacticDomin8r 9y ago
That's my point. The wiki definition you have cited is correct, but it doesn't compute with the article.
- DannyBee 9y ago
  I'll save everyone else the trouble. The original data is from https://www.aaafoundation.org/sites/default/files/2011PedestrianRiskVsSpeed.pdf https://www.aaafoundation.org/sites/default/files/2011Pedest... If you look, on page 9, you can see the plots of impact speed vs risk of death. They are clearly non-linear, and they you can also read that they tried various fitting methods for missing data (and quadratic best fit things). I'm just guessing that you are confused because it does not appear the constant for the x^2 term is >1.
  - GalacticDomin8r 9y ago
    I'll make it even easier: http://hyperphysics.phy-astr.gsu.edu/hbase/impcal.html#c1 http://hyperphysics.phy-astr.gsu.edu/hbase/impcal.html#c1
  - scotty79 9y ago
    Quadratic relationship is between the speed and force of impact. If you want to accelerate pedestrian to certain speed you have to pump kinetic energy into him. You do that by applying a force over some distance (distance is how much pedestrian will squish during impact before it starts moving with the car) so to acellerate to double speed, you need to pump in quadruple energy, you need to quadruple the force since squishing distance is the same (until you reach speeds that pulverize pedestrian bones).
- scotty79 9y ago
  f(x)=a*x^2 f(2*x)=a*(2*x)^2=a*4*x^2=4*a*x^2=4*f(x) Doubling the argument quadruples the value of quadratic function.
  - GalacticDomin8r 9y ago
    Try again using order of operations. It does not expand to (2*x)^2, it is simply 2x^2. To say it another way: 4x^2 != 2x^2

cozzyd 9y ago

2^2 = 4?