Bob Eisenman Posted June 18, 2018 Share Posted June 18, 2018 From a crash perspective, where a rider possessing kinetic energy (energy of motion) ultimately comes to a stop and has zero kinetic energy, the following physics equation deserves some thought. Kinetic energy Ek = ½mv2 For a rider of mass (m) in kilograms the one half times m part of the formula is a constant numeric quantity in the riders body KE crash value. Kinetic energy increases by the 'square' of the speed. So a Ninebot rider who normally goes up to 14 miles per hour (22.5 kilometers per hour) will have four times that kinetic energy if he/she crashes on an EUC travelling at (45 km per hr) 28 miles per hour . A factor of two squared in the KE equation. Increasing speed by a factor of three (motorcycle speed) increases the riders body kinetic energy by 9 (three squared) Dissipating the energy in some way during a crash determines the humans outcome as zero speed is ultimately attained. Speed and velocity have the same magnitude. Velocity is a vector quantity so a specific direction (ex 30 km per hr North) is required in its description. Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 13 minutes ago, Bob Eisenman said: Dissipating the energy in some way during a crash determines the humans outcome as zero speed is ultimately attained. Yes, the art of taunting the ground with small gestures of complacency while reducing your velocity. Just make sure not to cartwheel above 30 mph. Centripetal forces can be real $&!#! Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 I meat to say. Try not to cartwheel. Cartwheeling almost happens naturally above 30 mph. Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 59 minutes ago, Bob Eisenman said: Kinetic energy increases by the 'square' of the speed. So a Ninebot rider who normally goes up to 14 miles per hour (22.5 kilometers per hour) will have four times that kinetic energy if he/she crashes on an EUC travelling at (45 km per hr) 28 miles per hour . That is potential energy. This calculation would only Come into effect when hitting a brick wall. Hitting the road would be a form of deflection. Right? Link to comment Share on other sites More sharing options...
Bob Eisenman Posted June 18, 2018 Author Share Posted June 18, 2018 4 hours ago, RockyTop said: potential energy. In a faceplant the rider's center of mass drops to almost street level as the rider's potential energy (PE= mgh) is accelerated toward the ground by gravity (converted into kinetic energy). Cartwheeling is motion associated with rotational kinetic energy. PE and KE are combined to describe a riders energy. https://www.chem.wisc.edu/deptfiles/genchem/netorial/modules/thermodynamics/energy/energy2.htm PE and KE are described clearly in the text by 'Murphy and Smoot' which was a popular high school text book before using Google to extract the same information from places on the internet. Energy is the capacity to do work. https://en.m.wikipedia.org/wiki/Energy Link to comment Share on other sites More sharing options...
Bob Eisenman Posted June 18, 2018 Author Share Posted June 18, 2018 5 hours ago, RockyTop said: Cartwheeling Checkout this video https://youtu.be/kfY0PBDJgbM Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 Cartwheeling is also a term used when a person crashies and tumbles / spins too fast to pull his arms or legs in back in. This results in badly broken arms and legs. Cars and bikes can also cartwheel. It is ok for a race car but not a 280z at 170 mph. We had a 280z cartwheel at 170 mph on the interstate late at night. They had 1/2 mile of road blocked on both sides for a day picking up pieces. Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 Ok, so this brings up a good point. When you face plant the initial force is limited to gravity not forward momentum. Upon impact however your faces friction with the ground could try to slow your forward momentum. With the rest of your body still wanting to go forward your face becomes the fulcrum for a flipping motion. ( not good) A full face helmet would not only protect your face it would remove most of the friction. I would prefer not to use my face as a sticking point to slow my forward momentum. Link to comment Share on other sites More sharing options...
Chriull Posted June 18, 2018 Share Posted June 18, 2018 9 minutes ago, RockyTop said: Ok, so this brings up a good point. When you face plant the initial force is limited to gravity not forward momentum. ... Imo an additional force should add up: once the feet touch the bottom the forward moving body gets a torque accelerating the face downwards in addition to gravity. Once the knees hit the road friction could increase and strengthen this downward force. Link to comment Share on other sites More sharing options...
RockyTop Posted June 18, 2018 Share Posted June 18, 2018 4 hours ago, Chriull said: Imo an additional force should add up: once the feet touch the bottom the forward moving body gets a torque accelerating the face downwards in addition to gravity. Once the knees hit the road friction could increase and strengthen this downward force. Yes, I agree. This why I don’t do feet and knees other than to get me on my back. Additional force can definitely be added to gravity. And this is why your rubber face should never touch the road. I know that cut outs are too fast to react to but when possible I have always preferred a nice shoulder roll to the back and then balance out the abrasions til coming to a stop. Note other obstacles may apply. Link to comment Share on other sites More sharing options...
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