3 ms·
> mass multiplied by velocity equals momentum Isn't kinetic energy, ie. 1/2 m v^2, more appropriate for measuring the danger of vehicles?
by rwmj 3y ago
> mass multiplied by velocity equals momentum
Isn't kinetic energy, ie. 1/2 m v^2, more appropriate for measuring the danger of vehicles?
- frumiousirc 3y agoMeasures of danger (at least in terms of fatality) does seem to scale with velocity squared. I do not find info on various measures of danger may scale with mass. There is a huge connection between fatality and vehicle size, at least up to the size of today's giant trucks and SUVs (I do not find buses nor semis included). Of course size is correlated with mass. Though, what I read, the danger of today's trucks and SUVs is due to the high front end impacting human bodies where they are more vulnerable (torso instead of legs) and then dragging them under instead of allowing them to go over. OTOH, stopping distance and reaction distance is linear with velocity.
- eggman63 3y agoPhysicist here. Stopping distance is actually directly related to square of velocity. Work-Energy theorem: Work = ΔKE Force * distance = 1/2(mass)(velocity^2) distance α v^2 Slow down everyone :)
- frumiousirc 3y agoI agree with your analysis. I had conflated distance and time. And, I definitely agree with slowing down! Perhaps we can all start by actually obeying existing speed limits.
- colanderman 3y agoThe difference in mass between a pedestrian and any vehicle is so great that at the moment of collision, the pedestrian's velocity becomes that of the car, and the car's velocity is practically unchanged. (That is, energy transferred is a function of vehicle's velocity and pedestrian's mass.) Mass of the vehicle only practically comes into play for stopping distance, and as a proxy for its frontal cross-section.