So then I had to look for simple formula, and this in how I got it. Instead of calling 60 m.p.h. 87 odd feet per second, I called it 90 f.p.s. and that gave me the simple formula of adding half to my miles per hour to obtain speed in feet per second correct within 2 per cent. Ever since then I have driven cars, and tried running down cases in feet per second. Now what I say to all motorists is that they try doing what I do, that is, always to drive and think of speed in feet per second instead of in miles per hour, and you will at once become a hundred per cent better and safer driver. All you have to do is to add one half to the figure of your speed in m.p.h.
Any child can do that.
The other aspect of road safety touches what is called kinetic energy, which means the moving force possessed by a vehicle in motion. I can't give you a more detailed explanation, but another way to put it is to refer to kinetic energy as the kick possessed by a moving vehicle. A small motor oar weighing about a ton and moving at a speed of 40 miles per hour strikes the same blow as eighteen ten-ton steam rollers travelling at their highest speed, which is 3 miles per hour. The Listener October 1937, p. 892.