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I was reading that cutting your speed by only 10 MPH reduced the amount of energy released in a crash greatly. Since kinetic energy is proportional to the velocity squared, it makes sense. (KE=1/2*M*V^2) So I figured I would make an Excel spreadsheet and see for myself........

 

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yes back when I was doing construction we learned a 200lb man in a 6 ft fall his tie off point will recieve almost 5000lbs force thus the new shock absorbing lanyards and tieing off in 2 places.
 

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It's an even bigger deal than that. Stopping distance is ALSO affected as a second-order function of the speed at which you start...Every MPH you slow down, it requires less distance to slow the next MPH.

In the distance it takes to slow from 100 MPH to 95 MPH, a vehicle traveling 31 MPH could be stopped.

In the distance it takes to slow from 100 MPH to 90 MPH, a vehicle traveling 43 MPH could be stopped.

In the distance it takes to slow from 100 MPH to 70 MPH, a vehicle traveling 71 MPH could be stopped.

It works the same way at city speeds, too:

In the distance it takes to slow from 40 MPH to 30 MPH, a vehicle traveling 26 MPH could be stopped.
 

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And all this data is fine , but really means nothing unless you are trying to make some point about impact energy. Speed is of course relitive...relitive to what is the question here...lol.

Simply, do not go fast unless you have the time and space to slow/stop if something calls for it. Going 150 mph does not kill you. But don't try going that fast unless you not only have a safe/secure bike...but also a remote and empty stretch void of other traffic.

Our poor bodies can only absorb so much energy before parts fail. An impact to a helmeted head at 25 mph may only cause a minor concussion, but the same impact at 30 could kill you.....so realizing the needed stopping distances you need for a particular speed is valuable info to have.

KM
 

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Discussion Starter #6
It's an even bigger deal than that. Stopping distance is ALSO affected as a second-order function of the speed at which you start...Every MPH you slow down, it requires less distance to slow the next MPH.
How is distance a second order function of speed? I think you mean acceleration.......

In the distance it takes to slow from 100 MPH to 95 MPH, a vehicle traveling 31 MPH could be stopped.

In the distance it takes to slow from 100 MPH to 90 MPH, a vehicle traveling 43 MPH could be stopped.

In the distance it takes to slow from 100 MPH to 70 MPH, a vehicle traveling 71 MPH could be stopped.

It works the same way at city speeds, too:

In the distance it takes to slow from 40 MPH to 30 MPH, a vehicle traveling 26 MPH could be stopped.
These numbers look right....( I'm curious where you got them?) mathmatically anyway. ( V(stop)=sqrt(Vi^2-Vf^2) ) But this assumes the same acceleration, and that just ain't gonna happen ( reaction time distance, not to mention the friction coefficient is different at different speeds, and so on, blah, blah...... ) Of course your point is right on..... Stopping distance is increases with speed, hence the two second rule for minimum following distance. ( as per MSF guidelines)
 

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And all this data is fine , but really means nothing unless you are trying to make some point about impact energy. Speed is of course relitive...relitive to what is the question here...lol.
That was my point.... impact energy increases as a function of the speed^2, therefore speed is 'relitive' to how much energy is released in a collision :)

Simply, do not go fast unless you have the time and space to slow/stop if something calls for it......
Yes, and the point of the story I was reading was to learn and practice emergency stopping. The quicker you can decelerate makes a huge difference in how much damage the resulting collision is going to have. :smiley_th
 

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Discussion Starter #8
Sorry, but when I see numbers I have to figure out where they came from......
Below is a photo of how I checked out ImBoring's data. It was a fun math exercise :blah:

 

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I guess I don't need to show the second-order nature of stopping distance vs. initial velocity any more, since you just did it, complete with some underlying calculus...Nice. :)

I find that very poignant. In the worst-case, no-time-to-react scenario, the energy released in a crash decays with the square of a reduction in speed, which was how you started the thread.

However, if you have time to react, the benefit of the slower starting speed is also seen in the amount of speed you can scrub off, so the speed at impact (If any impact even still occurs) is reduced by MORE than the initial reduction of speed at the start of the emergency braking event, and it is that speed at impact which is squared to determine the proportionality of the energy released, so you see what might be called a snowball effect.
 

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Avoiding the Thump

Spot on Guys. :wow:

When I first started riding it seemed cars were pulling out on me, when in actuality my over the speed limit driving caused the drivers to misjudge my actual closing speed. I now ride speed limit or less in town, added a Head Lamp Modulator, and LED Brake-Flash Lights to license plate.

That being said, Emergency Stopping was one of the biggest learning experiences I had in the safety course. Keeping my balance with all of that energy being absorbed into the suspension system was a challenge. (learning to stand on the pegs and balance the bike helped a-lot)

Braking fast and looking for "away out" of the collision is a combination to think about and consider.

Do you Emergency Brake, then slowly point for that ditch to avoid a truck that is crossing your path? After-all, that ditch may be a bit softer than the side of a truck.

Each situation is unique and each rider's bike and ability is different.

I find myself "looking for away out" even when there is no clear emergency.
I do this to cut reaction/decision time down. I also keep my distance from other motorist, because let's face it; no matter who is at fault, in the end the rider is going to loose some skin. :(

:blah:
 

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Discussion Starter #11
I remember my MSF instructor saying over and over, "The motorcycle never wins." We spent a lot of time on emergency braking, stopping in a curve, swerving, and cornering technique. One of the biggest things I took away from the course was to keep my head and eyes up at all times, and turn your head where you want the bike to go. If your focus is on that guard rail coming at you in a twisty, your gonna hit it.
 

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Kinetic energy = mass X velocity squared, I just learned this in physics today. If you double your speed your kinetic energy is quadrupled meaning the the inertia (resistance to change in movement) is greatly increased, which means possible harder and further ejection, more powerful impact, and more serious injury; plus an increased risk of death, but we already knew that part.
 

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Kinetic energy = mass X velocity squared, I just learned this in physics today. If you double your speed your kinetic energy is quadrupled meaning the the inertia (resistance to change in movement) is greatly increased, which means possible harder and further ejection, more powerful impact, and more serious injury; plus an increased risk of death, but we already knew that part.
Way back when I was in engineering school I used to calc the velocity at which I'd hit the pavement in the event of a mishap:wow:
 

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You've just got to ride with the presumption that you are invisible to the cars out there. Keep an eye on your mirror at stops, and leave enough room in front of you to be able to escape if you see someone barreling up behind you.

Approach intersections carefully, as cars WILL pull out in front of you.

Riding a dirt bike is a lot less stressful when it comes to the possibility of life ending collisions with large steel objects... and the 'I' beams that guardrails are attached to. :)
 
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