Halleluja, I've been trying to tell cyclists this for years, but it's like banging my head against a brick wall (with or without a helmet).
Anyone who thinks that total kinetic energy is a sensible metric for gauging the potential to cause harm might be interested to know that the KE of a 72kg cyclist travelling at 12mph is exactly the same as Dirty Harry's Magnum 44 (1037J, 16g & 360m/s, to save looking it up).
Energy dissipated in the impact is a big step in the right direction but even that doesn't cut the mustard, as a simple thought experiment demonstrates: if a stuntman jumps from a skyscraper the outcome will be very different depending on whether he lands on the pavement or an airbag, even though the KE and total dissipated energy are the same in each case.
What differ are contact area and modulus of the materials, hence stopping distance & acceleration, hence force & pressure. Soft compressible materials increase the stopping distance so reduce acceleration and force, and large contact areas reduce pressure. Materials that dissipate energy rather than storing it stop the motion rather than making objects rebound and continue their motion in another direction.
People are fond of pointing to the mass of a vehicle too, but that makes virtually no difference beyond a certain limit: the force exerted on a 70kg cyclist in the way of a 1000 ton train travelling at 30mph isn't that required to stop the train dead, it's the force required to accelerate the cyclist to 30mph. The energy dissipated in the impact with the train is twice as much as from another cyclist crashing into him at the same speed. Not 14,000 times as much, just twice.
How I broke two fingers when I fell over six years ago, and how I cut the same two fingers 30 years earlier when my reflexes made me grab a barbed wire fence.Nearholmer wrote: 30 May 2025, 9:48am Flinging your hands out when falling forward is an obvious instinct