Runners: Why are you too good for the sidewalk?

[SpatiallyAware]

You're getting hung up on 0.25" of compression in a very specific circumstance. That was a peak compression from a 200lb person running, which could result in more than 700lbs of force acting on the asphalt. If you can't understand how this is different than your retarded, contrived situation, then there's really not much else to say. I knew before I submitted that message that someone would get hung up on that number, but I figured repeated explanations would help clear it up. I guess not.

Now, onto your stupid experiment. I was VERY easily able to feel movement under my thumb when I pressed it into the road. Concrete has exactly zero give when using the same pressure from my thumb. I also found a sizable piece of asphalt to compress between my fingers. Video.

No, it isn't popping back into shape very quickly, but I'm also putting very different load on it with my finger. I can't emulate running with my thumb. However, I can very easily show how compressible asphalt is compared to concrete with relatively little force.

Look, you might be able to slowly press into a thin asphalt and make a dent, but I assure you that this has a negligible affect to an instant hit like you would get from running. It's similar to some of the closed cell foam demonstrations.... It's not the same sort of physics exercise when you tap on something as a 200lb runner for 1/8 of a second.


Past that, I flat out do not believe that a runner is compressing the asphalt by .25". I have a good bit of experience messing with compressing hot asphalt, and it's a very very slow thing. Even the point of a motorcycle kickstand (about the size of a quarter), with ~200lb of weight on it will still take a solid 5 minutes to actually start poking through the asphalt.

I just don't believe that a shoe surface, which is inherently designed to spread load, is going to compress hot asphalt by any significant amount while running. Maybe while stand still on your tip toes for a few minutes or something, but that's a different activity.


I am not any sort of anti-runner, but this argument that asphalt is softer and thus justifies you running in traffic is absolutely stupid.

 

[WelshBloke]

Firstly I love you so much for going outside and making that video. :thumbup:

I'm not arguing that asphalt isn't more pliable than concrete.
I was just disagreeing with you in the way it would act. I don't think it would compress anywhere near the amount you were claiming and that it would do anything particularly quickly.

But still. Kudos for the video though.

 

[MrDudeMan]

Firstly I love you so much for going outside and making that video. :thumbup:

I'm not arguing that asphalt isn't more pliable than concrete.
I was just disagreeing with you in the way it would act. I don't think it would compress anywhere near the amount you were claiming and that it would do anything particularly quickly.

But still. Kudos for the video though.

I was bored and you presented an opportunity for more internet arguing.

I see what you're saying. I'm going to see if I can somehow capture the compression if I run on it. I don't have particularly good running form or high quality video equipment, so I don't really know if I'll be able to get anything worthwhile.

 

[SpatiallyAware]

And huge props on the video. :thumbsup::thumbsup:



Here's what I would like to see... A blind test with a couple of runners, all wearing blindfolds and earplugs, to differentiate between concrete and asphalt.

 

[MrDudeMan]

Look, you might be able to slowly press into a thin asphalt and make a dent, but I assure you that this has a negligible affect to an instant hit like you would get from running. It's similar to some of the closed cell foam demonstrations.... It's not the same sort of physics exercise when you tap on something as a 200lb runner for 1/8 of a second.

You should familiarize yourself with how materials behave in the realm you can't comprehend with your senses. There's a frequency component that's both important and not perceptible. A good example is a tennis ball hitting a wall. You'd never see this with your eye and the impact is so quick that the deformation isn't permanent. There's absolutely no reason why the road wouldn't do the same thing. I hear what you're saying, but the compressibility of the material is a known constant.

Past that, I flat out do not believe that a runner is compressing the asphalt by .25". I have a good bit of experience messing with compressing hot asphalt, and it's a very very slow thing. Even the point of a motorcycle kickstand (about the size of a quarter), with ~200lb of weight on it will still take a solid 5 minutes to actually start poking through the asphalt.

See above.

I just don't believe that a shoe surface, which is inherently designed to spread load, is going to compress hot asphalt by any significant amount while running. Maybe while stand still on your tip toes for a few minutes or something, but that's a different activity.

It doesn't take a few minutes to make a dent. It took less than a second for just my thumb to make an impression. I gave you a worst case example, so don't get hung up on 0.25". Realistically it's probably between 0.025" and 0.050", but that's a non-trivial amount of compression compared to the rubber in a shoe and concrete compresses far less. Those are the points I'm making.

I am not any sort of anti-runner, but this argument that asphalt is softer and thus justifies you running in traffic is absolutely stupid.

No one said we should start running in traffic. Your statement is off-topic. Running in traffic is, in fact, stupid.

 

[MrDudeMan]

And huge props on the video. :thumbsup::thumbsup:



Here's what I would like to see... A blind test with a couple of runners, all wearing blindfolds and earplugs, to differentiate between concrete and asphalt.

I'll see what I can do. I think they'll need earplugs as well because concrete makes a different sound.

 

[Jeff7]

I had a longer conversation with my bro-in-law to try to get more information.

The modulus of elasticity determines how much deformation occurs in a material with a given load in the elastic region. The elastic region is defined as the range of loads starting from 0 to the point where the load becomes high enough to cause permanent deformation. With that said, the modulus of elasticity of asphalt in compression (which is the state it's in while you're running on it) is 0.2 ksi. 1 ksi = 1000 lbs per sq. in. The modulus of elasticity of concrete is 3 ksi. That means a load that causes a deformation of x on concrete will cause a deformation of 15x on asphalt.

Some math:

I previously calculated that a 200 lb human could put as much as 100 psi (rounded down for a whole number) on his foot at the moment of impact. A shoe probably reduces that by a factor of 4 (I failed to mention this earlier) because of the distributed load due to the sole of the shoe. So, a 200 lb person could put 25 psi of pressure on an asphalt road. That's 12.5% of the modulus of elasticity, meaning if the asphalt is 2" thick, it will compress 0.25" very briefly. Concrete would compress by 0.016". Even if the pressures are off by a factor of 3, asphalt would still compress noticeably more than concrete. My shoe compresses about 0.4", so an asphalt road compressing by even 0.05" would be noticeable (12.5%).

Those are peak numbers. Reduce the pressure exerted by the same person by 50%, which is more realistic for long distance running (force per step = body weight * 1.75 (instead of 3.5 like I used earlier)). Now the asphalt compression is roughly 6%. Changing the thickness of the asphalt, compression of the shoe, weight of the runner, and several other things will obviously affect the results. It may turn out to be less than 1% in some cases, so I doubt a person in that situation would be able to feel the difference. However, it could end up being close to 10% in other situations and I strongly believe a person can feel that. Note: this is all at 25C. The modulus of elasticity decreases as temperature increases, so on a hot day the asphalt will be weaker while concrete stays essentially constant at all survivable ambient temperatures.

As it turns out, my previous comments about asphalt returning the same amount of energy were incorrect. It should definitely return less as it absorbs much more than concrete. I read some of that on my own, but I trust this new information much more as it came from someone who I trust is an expert in this field.

I didn't know that asphalt was so soft...at least under slower loading conditions
I'm certainly more willing to entertain that my position on this is quite incorrect. (I'd still love to see the graphed output from a pressure transducer or accelerometer though.)

That's also under static loading though; this is, as you said, a transient, or impact-loading scenario. The asphalt would not have much time to deform, though I will say, a reduction in the time to decelerate from one very brief period of time to a slightly-less-brief period of time, such as 0.5ms to 10ms would indeed yield a directly-proportional reduction in the apparent force experienced by the runner's shoe.
I'm guessing that's what we'll see: Concrete will show a sharper spike in deceleration upon impact, whereas asphalt's will be a longer spike, and lesser in amplitude. Then I'd also like to see, obviously, how much of that gets sent through the shoe. I'm thinking there will be two spikes: One on initial impact, and then another when maximum compression of the shoe is reached.


Adding to the fun: I've now got a model of asphalt in my mind now similar to the mixture of cornstarch and water - a liquid with small solid particles suspended in it. The duration of loading suddenly becomes a big deal. I'd imagine that a quick whack with a bag filled with 20lbs of cornstarch and water would knock a person over, and leave a decent bruise, or even break a few small bones, whereas a slow application would result in no injury whatsoever. I wonder then how asphalt behaves under these transient loading conditions, and whether or not the static loading methods can be properly applied?

 

[bradly1101]

It just seems dangerous.

In the last few years where I live they've introduced 'bike share lanes' where they take the right lane of a busy street (or on some one-lane streets, the whole lane) and encourage bikes to use the whole width of the lane. It's marked, but drivers don't like slowing down and often get very close. The law here in CA treats bikes and cars the same.

Like with runners the difference in speed just makes it too dangerous.

 

[silverpig]

You're getting hung up on 0.25" of compression in a very specific circumstance. That was a peak compression from a 200lb person running, which could result in more than 700lbs of force acting on the asphalt. If you can't understand how this is different than your contrived situation, then there's really not much else to say. I knew before I submitted that message that someone would get hung up on that number, but I figured repeated explanations would help clear it up. I guess not.

Now, onto your experiment. I was VERY easily able to feel movement under my thumb when I pressed it into the road. Concrete has exactly zero give when using the same pressure from my thumb. I also found a sizable piece of asphalt to compress between my fingers. Video.

No, it isn't popping back into shape very quickly, but I'm also putting very different load on it with my finger. I can't emulate running with my thumb. However, I can very easily show how compressible asphalt is compared to concrete with relatively little force.

Go take a heavy sledgehammer, ram it into the asphalt from over your head as hard as you can, and measure the depth of the dent. I'd be surprised if you compressed the asphalt more than .25"

You are assuming the asphalt can take .25" of elastic compression before it gets into plastic deformation.

Flip a nail upside down so its head is on the road, then load a 45 lb plate on it (you can keep it balanced with your hand). It won't sink in much unless you leave it there for a long time. A foot strike is a fraction of a second.

 

[silverpig]

LOL. And the shoe is going to absorb the full impact no matter what the surface? LOL.

HAHAHAHA No. HAHAHAHA.

LOL

facepalm

 

[SpatiallyAware]

I've always used the sidewalk when running.

Pretty sure 1/2 the people in this thread are olympic class athletes who should be training on a track anyway.


Starting today I am honking at any idiot running in the road when a sidewalk is available.

 

[MrDudeMan]

Go take a heavy sledgehammer, ram it into the asphalt from over your head as hard as you can, and measure the depth of the dent. I'd be surprised if you compressed the asphalt more than .25"

You are assuming the asphalt can take .25" of elastic compression before it gets into plastic deformation.

Flip a nail upside down so its head is on the road, then load a 45 lb plate on it (you can keep it balanced with your hand). It won't sink in much unless you leave it there for a long time. A foot strike is a fraction of a second.

For the love of god, 0.25" was a worst case calculated value in a specific circumstance. Shut the hell up about 0.25" already. I said multiple times in that exact same paragraph that the real value was likely much lower. That result was calculated with a ton of assumptions, including the most important one - the thickness of the asphalt.

The biggest takeaway from that post that everyone seems to be missing is that asphalt is much softer than concrete, which was one of the original issues in this thread. Get past the numbers - the ratio is what's important.

I tried your experiments even though neither of them has anything to do with the situation in this discussion. I can't create 700 lbs of force with a 27 lb sledgehammer, but it still sunk approximately 0.103" into the asphalt. The asphalt on my road also isn't 2" deep, so that ratio is actually close to the value I calculated. I do think that's worse than a foot would be even for a split second, though.

Putting a 45 lb plate on the head of a 4d nail created a dent immediately. It did continue to slowly sink as time went on.

A 2" thick section of asphalt could compress by 0.25" and still be elastic. The stress-strain curve says that should be fine.

 

[SpatiallyAware]

You are measuring nail depth to .103????



I won't be happy unless you do a blind test with multiple people.

 

[alkemyst]

Pretty sure 1/2 the people in this thread are olympic class athletes who should be training on a track anyway.


Starting today I am honking at any idiot running in the road when a sidewalk is available.

I'd love to see you blow a stop sign when someone like me catches up to you at the intersection.

 

[SpatiallyAware]

I'd love to see you blow a stop sign when someone like me catches up to you at the intersection.

LOL I love it when someone like you puts your foot in your mouth.



"Someone like you".... Says so much. Sitting here laughing at ya, bud.

 

[alkemyst]

Everyone is a tough guy on the Internet.

 

[SpatiallyAware]

Everyone is a tough guy on the Internet.

You really don't get the irony of you saying that?

 

[alkemyst]

You really don't get the irony of you saying that?

I am the real deal while those like yourself threaten while hiding behind the screen.

You going to be the big man and honk at mopeds and cyclists too?

 

[Anubis]

so your gonna hulk smash a car if it honks at you?

 

[SlitheryDee]

This thread has gotten predictably derailed. Who cares whether asphalt is softer than concrete? I didn't think this was about runners running on sidewalk all the time anyway. This thread was initially about runners staying in the road and making cars drive around them or creep behind them until an opportunity to pass came wasn't it? That's all I care about. I say run on the road until a car comes and then get out of the way. Hop on the sidewalk if there is one for the brief time that cars pass. Hop back on the road when it's clear. Surely the few minutes or seconds that will take can't damage your wittle sensitive knees can it?

Sadly I know that quite a few runners won't even give that much. It's got to be as perfect for them as possible all the time and nothing less will do. I'm not even mad at them for running in the street. It's the attitude that does it. It's the exact same "fuck you all I'm doing what I want" attitude that causes people to continue screwing around with their cell phones during movies. It's also the same attitude that smokers who keep lighting up around other people have, despite the fact that it's well known that most people hate the smell. That's probably the comparison runners don't want to believe because they love to hate smokers. Hear that runners? You're just like the people you hate the most.

 

[Train]

This thread has gotten predictably derailed. Who cares whether asphalt is softer than concrete? I didn't think this was about runners running on sidewalk all the time anyway. This thread was initially about runners staying in the road and making cars drive around them or creep behind them until an opportunity to pass came wasn't it? That's all I care about. I say run on the road until a car comes and then get out of the way. Hop on the sidewalk if there is one for the brief time that cars pass. Hop back on the road when it's clear. Surely the few minutes or seconds that will take can't damage your wittle sensitive knees can it?

Sadly I know that quite a few runners won't even give that much. It's got to be as perfect for them as possible all the time and nothing less will do. I'm not even mad at them for running in the street. It's the attitude that does it. It's the exact same "fuck you all I'm doing what I want" attitude that causes people to continue screwing around with their cell phones during movies. It's also the same attitude that smokers who keep lighting up around other people have, despite the fact that it's well known that most people hate the smell. That's probably the comparison runners would hate the most because they love to hate smokers. Hear that runners? You're just like the people you hate the most.

Ooh, you mean like drivers who can't be bothered to slow down for 5 friggin seconds to share the road?

 

[Wyndru]

I'm guilty of not stopping or swerving from time to time. Especially on busier main roads. If there is a heavy steam of oncoming traffic I won't swerve or stop until I have room to go around. I figure if the runner/biker is comfortable to run on the road in a location like that then they probably won't have an issue getting hit with some extra air pressure from my car.

I'm always afraid someone is going to slip or trip and I run them over though. We have a lot of parks where I live, I've never understood the need to exercise on the main roads.

 

[SpatiallyAware]

<snip>

It's the attitude that does it. It's the exact same "fuck you all I'm doing what I want" attitude that causes people to continue screwing around with their cell phones during movies. It's also the same attitude that smokers who keep lighting up around other people have, despite the fact that it's well known that most people hate the smell. That's probably the comparison runners don't want to believe because they love to hate smokers. Hear that runners? You're just like the people you hate the most.

Yup, exactly right, except in this case the runners aren't paying for the road.

So, it would be like someone sneaking into a movie, then having a loud phone conversation for 5 minutes because "everyone should just be a little patient!"

 

[SpatiallyAware]

I am the real deal while those like yourself threaten while hiding behind the screen.

You going to be the big man and honk at mopeds and cyclists too?

I don't discriminate, I honk at anything which needlessly or stupidly holds me up in traffic for longer than about 5 seconds.

And if it's rush hour I will lay down the horn for a good 10 seconds as I drive by while pointing at you and laughing.



And please, please just stick a hand in the window, or throw something at my car which would likely cause me to reasonably fear for my life.

 

[SpatiallyAware]

I'm guilty of not stopping or swerving from time to time. Especially on busier main roads. If there is a heavy steam of oncoming traffic I won't swerve or stop until I have room to go around. I figure if the runner/biker is comfortable to run on the road in a location like that then they probably won't have an issue getting hit with some extra air pressure from my car.

I'm always afraid someone is going to slip or trip and I run them over though. We have a lot of parks where I live, I've never understood the need to exercise on the main roads.

It's the elitist attitude... I mean look at this thread, or any thread that talks about bicyclists using an entire line holding up piles of traffic.

Of course they could go to parks or stick to low traffic areas, but then they can't show off their latest skin tight outfit.


I seriously think that vast majority of bicyclists are insecure about their sexuality and are trying to express themselves in some weird repressed manner.