OldXCguy wrote:
This just proves that people weren't meant to run on a treadmill, since it's contrary to the laws of physics.
It also proves a lot of people don't know what the words "inertia" and "momentum" mean. Hint: You can't use the words interchangeably. Everyone mentioning the "inertia" of a moving object needs to refer back to Citizen Runner's post.
Conundrum - Just admit you are wrong. Google it.
Sprint Geezer wrote:Consider this: I have a hard time breaking 20 minutes for a 5k on a treadmill (I am a 5'10" 182-lb sprinter). When I found out on letsrun that people consider 20 minutes a mere jog, I felt like an idiot, even though I don't train for the 5k distance. So I tried a 5k outdoors, on a track, wearing flats.
I finished relatively easily in 18 minutes! I could have gone substantially faster.
So I returned to the treadmill and found that I got fatigued running at 10 mph! Thinking that there was something wrong with the treadmill, I tried 2 others, different brands entirely, and got the same result.
Anybody else experience something similar?
you are a bullshitter or a moron
actually both
there are numerous mentions of great treadmill runs
the smart guy above gave the clue when he mentioned 0 wind for a treadmill :
it implies you must find the running speed on the track corrected for same numerical -ve wind speed as that, which = your treadmill speed
therefore a treadmill 5k worth, outdoors using mureika's wonderful wind/altitude calculator :
20'00 ->~ 21'50
15'00 ->~ 16'23
13'00 ->~ 14'12
ask me nicely & i'll tell you what you need to run on a treadmill to =
3'26 or 7'20 or 12'37 or 26'17
Back to High School Physics with youmomentum=Mass*Velocity. On a treadmill, V=0
Uncle Rico wrote:
Conundrum wrote:No momentum since your body is not moving foward. You could have minimum and momentary momentum in your foot and lower leg during the short time it moves forward.
wrong, your body is moving relative to the belt and that is all that matters
i'll also thrown in 1'41.0 sometime
Sprint Geezer is right. At least for those of us with mesomorphic, dare I say more manly builds.
"When the same athlete runs on a treadmill, centre of mass is static (at least in the forwards-backwards plane). There is no forward progress; instead, the running surface 'disappears' behind the athlete. In fact, the treadmill belt moves the athlete's legs and feet under and behind her centre of mass and, to preserve stability, their key task is to move the support leg back in front of the centre of mass in time for the impact with the treadmill belt. The key function of the leg muscles during treadmill running is not to produce propulsive forces but to re-position the legs so as to keep the centre of mass stable."
The effect is less pronounced for pencil necked geeks.
Okay, I follow that.
Here's my follow up question to anybody who can answer it:
Consider a bouncy ball dropped from above the treadmill. The higher above the treadmill it is dropped from, the longer it falls, the faster it hits the belt at.
My first assumption: The faster the ball hits the belt, the less time it spends in contact with the belt. I'm not sure that this is true, but it seems likely to me for some reason.
If this is true, the faster the ball hits the treadmill, the less time the treadmill will be able to exert force on the ball, the less it will cause acceleration in the rear-facing vector (toward the back of the treadmill). So, the faster the ball is travelling when it hits the ball, the less rearward force will be imparted. This is obviously not a linear relationship to the angle the ball will leave the treadmill or how far down the treadmill (or off it) the ball will bounce, but less it seems like the effect would be similar to a golf ball bouncing down the cart path vs. the fairway vs. the ruff (less friction in golf being compared with less treadmill contact time for the ball).
If there is an analogy in elasticity and impact in runners tendons/legs, then it seems that those runners with a more effective tendon/ligament elasticity and those with shorter ground contact time would have an easier time running on a treadmill. The reason would be that the treadmill would spend less time imparting rearward force to the runners body through the legs. In other words, assuming two runners apply the same amount of horizontal vector force per footstrike, but a different amount of vertical force per footstrike (caused by better elasticity, for instance), the runner with the higher vertical force is going to be better at treadmill running relative to normal ground running. The reason would be that the ground gives just a normal force and the treadmill actually applies a force in a specific direction?
I'm thinking that there is a logical error somewhere in this thought, but I can't tell where. My guess is that there is a corresponding frictional normal force on regular ground, or that I'm still conflating the two different inertial reference points in my ball analogy, and so it only carries over to the first few steps on a treadmill for a runner. If anyone can sort through this and give me an answer, I'll be very happy.
While your velocity is zero relative to the treadmill as a whole and the room you're in, you have a nonzero velocity equal to your running speed equal to the belt of the treadmill. For those who say running on a treadmill is easier because there is no air resistance (makes sense given that your velocity relative to the air in the room is also zero, which isn't the case if you're not on a treadmill), I would say that this also comes at a disadvantage. When you're not on a treadmill, your body is moving through stationary air, so your excess body heat is transferred to a "new batch" of air at all times. When you're on a treadmill, the air surrounding your body gets warmer and warmer, making it more difficult for you to radiate the heat away. So cooling is much less efficient on a treadmill than it is outdoors, all else being equal.
Of course, having a fan blow on you would fix that.
If the belt suddenly stopped, a block being slid on the treadmill would NOT move forward. It has no momentum. Try it. Keep a block in place with your hand behind it, put the treadmill on high, and gradually slide it to the side off the treadmill.You won't feel any forward momentum propelling is forward. Empirical evidence...End of thread. No momentum.
Demotivator wrote:
Everything is relative to your frame of reference. You have inertia relative to the belt. Case in point: if the belt were to suddenly stop (not gradually slow), you would fall forward.
http://en.wikipedia.org/wiki/Inertia#Inertial_frames"In a location such as a steadily moving railway carriage, a dropped ball (as seen by an observer in the carriage) would behave as it would if it were dropped in a stationary carriage. The ball would simply descend vertically. It is possible to ignore the motion of the carriage by defining it as an inertial frame. In a moving but non-accelerating frame, the ball behaves normally because the train and its contents continue to move at a constant velocity. Before being dropped, the ball was traveling with the train at the same speed, and the ball's inertia ensured that it continued to move in the same speed and direction as the train, even while dropping. Note that, here, it is inertia which ensured that, not its mass.
In an inertial frame all the observers in uniform (non-accelerating) motion will observe the same laws of physics. However observers in another inertial frame can make a simple, and intuitively obvious, transformation (the Galilean transformation), to convert their observations. Thus, an observer from outside the moving train could deduce that the dropped ball within the carriage fell vertically downwards.
However, in frames which are experiencing acceleration (non-inertial frames), objects appear to be affected by fictitious forces. For example, if the railway carriage were accelerating, the ball would not fall vertically within the carriage but would appear to an observer to be deflected because the carriage and the ball would not be traveling at the same speed while the ball was falling. Other examples of fictitious forces occur in rotating frames such as the earth. For example, a missile at the North Pole could be aimed directly at a location and fired southwards. An observer would see it apparently deflected away from its target by a force (the Coriolis force) but in reality the southerly target has moved because earth has rotated while the missile is in flight. Because the earth is rotating, a useful inertial frame of reference is defined by the stars, which only move imperceptibly during most observations.The law of inertia is also known as Isaac Newton's first law of motion.
In summary, the principle of inertia is intimately linked with the principles of conservation of energy and conservation of momentum."
Conundrum wrote:
If the belt suddenly stopped, a block being slid on the treadmill would NOT move forward. It has no momentum.
In this analogy, while the treadmill is running, the block has two equal and opposite forces acting on it, the friction from the belt trying to push it to the back of the treadmill and a balancing force pushing it toward the front. When you stop the belt both forces go to zero in the same manner so the net force on the block is always zero and there is no change in the block's momentum in any non-accelerating reference frame.
To an observer not on the belt the block was never moving and thus had zero momentum as you say.
An observer fixed to the belt would see the block as moving and it would have momentum relative to him. If he smacked into the block it would hurt, see brick wall analogy from previous append. When you stop the belt in this belt-relative reference frame, you've accelerated the reference frame. This both makes this a very messy analogy and removes it from the act of steady state running on a treadmill. The observer would feel that he's been accelerated to the same velocity as the block so he and the block would have zero relative momentum. If he were just about to smack into the block when the belt stopped he would breathe a sigh of relief.
psychic wrote:
Back to High School Physics with you
momentum=Mass*Velocity. On a treadmill, V=0
Uncle Rico wrote:wrong, your body is moving relative to the belt and that is all that matters
Back to HS physics? I've already had my share, and I must have been decent at it or I would not have gotten my engineering degree. Velocity relative to the earth is zero yes, BUT velocity relative to the belt is not and that is all that matters. You have momentum relative to the belt. There are plenty of posts explaining why. If I had an infinitely long treadmill and you were standing on it blindfold while it was running you would not know that you were moving relative to the earth. Much like we don't see that the earth is rotating at 1000mph.
Fairly basic really. wrote:
When you pushoff the ground it is solid.
When you pushoff the treadmill it is moving away from you.
When you are running on the treadmill, whenever you have both feet off the belt it is still moving in the opposite direction.
If you bounce on the spot with the belt running it will still record that you are moving forward.
Please don't tell me you think that if one jumps up and down on a treadmill that you are gaining free distance.
If you bounce on the spot with the belt running you will bounce backwards right off the treadmill unless you counter the backwards force of the belt but jumping forward. This forward jumping is the same as if one were jumping forward on the ground, even though it will appear that you are just jumping straight up and down.
wobblegobblurrr wrote:
Okay, I follow that.
Here's my follow up question to anybody who can answer it:
Consider a bouncy ball dropped from above the treadmill. The higher above the treadmill it is dropped from, the longer it falls, the faster it hits the belt at.
My first assumption: The faster the ball hits the belt, the less time it spends in contact with the belt. I'm not sure that this is true, but it seems likely to me for some reason.
If this is true, the faster the ball hits the treadmill, the less time the treadmill will be able to exert force on the ball, the less it will cause acceleration in the rear-facing vector (toward the back of the treadmill). So, the faster the ball is travelling when it hits the ball, the less rearward force will be imparted. This is obviously not a linear relationship to the angle the ball will leave the treadmill or how far down the treadmill (or off it) the ball will bounce, but less it seems like the effect would be similar to a golf ball bouncing down the cart path vs. the fairway vs. the ruff (less friction in golf being compared with less treadmill contact time for the ball).
If there is an analogy in elasticity and impact in runners tendons/legs, then it seems that those runners with a more effective tendon/ligament elasticity and those with shorter ground contact time would have an easier time running on a treadmill. The reason would be that the treadmill would spend less time imparting rearward force to the runners body through the legs. In other words, assuming two runners apply the same amount of horizontal vector force per footstrike, but a different amount of vertical force per footstrike (caused by better elasticity, for instance), the runner with the higher vertical force is going to be better at treadmill running relative to normal ground running. The reason would be that the ground gives just a normal force and the treadmill actually applies a force in a specific direction?
I'm thinking that there is a logical error somewhere in this thought, but I can't tell where. My guess is that there is a corresponding frictional normal force on regular ground, or that I'm still conflating the two different inertial reference points in my ball analogy, and so it only carries over to the first few steps on a treadmill for a runner. If anyone can sort through this and give me an answer, I'll be very happy.
Your logical error is that there is a rearward force from the treadmill to the foot. Think of the air port moving sidewalks. You put your hand on the moving rail, do you feel the rail pulling your hand? No. By the same physics, the forces between your foot and ground act exactly the same way as foot and belt.
Trolling right? I don't want to have to respond to this one because it would be so much work trying to understand how you came up with this notion.
hipster doofus wrote:
Trolling right? I don't want to have to respond to this one because it would be so much work trying to understand how you came up with this notion.
Are you talking to me? I just meant he got it backwards. The foot is what is producing the rearward force, the treadmill produces the equal/opposite force forward. Draw a free body diagram.
Uncle Rico wrote:
.........You put your hand on the moving rail, do you feel the rail pulling your hand? No. ...................
Also, to clarify, the "moving rail" is moving at the same rate as the airport sidewalk you are standing on. So zero velocity relative to the belt and you.
This is true for a lot of people. I have trouble dumping heat so no wind is a huge negative for me. I run about 1-2 minutes/5k slower on a treadmill than outdoors at say 75F.
It depends on what is limiting you.
My physics degree is telling me that, after the initial acceleration phase (which is definitely different), the only differences between treadmill and normal are the air resistance and the surface underfoot.
I was having coffee with a world-class masters' sprinter this morning - also an extremely knowledgeable guy - and he said that treadmills just didn't work for sprinters; he's quite adamant that you move differently. Very similar to what Sprint Geezer says.
However, my common sense is telling me that when there is snow and ice outside, doing long reps or tempos on a treadmill, with your muscles warm and comfortable, is a hell of a lot better than (a) risking slipping and sliding around in the cold, or (b) doing some non-running thing like swimming or biking.
Ok yeah, I guess it all makes sense now.
Going from the physics to the feel though, I guess if I imagine the treadmill having negative incline (the back propped up as if you were running downhill), then I might be able to make the example more pronounced and visualize what's going on.
So running downhill on land, my momentum naturally builds and I begin rolling along faster and faster. At first I had trouble visualizing this on a negative incline treadmill, but I suppose the equivalent of beginning to build momentum on the downhill treadmill is the end result of running off the front of it (given the speed is constant). As simple as it is I guess it was just a psychological thing I overlooked in that during my tempo run every moment I started building momentum and started rolling I would push the increase speed button (rather than run off the front ha).
Yeah, even after getting past the physics of the treadmill itself, i can't look past the fact that I land and pushoff differently from a treadmill.
After my tempo I found my front big toes were extremely tired and blistered on the inside. It was like I had been gripping the treadmill to push off.
It might be the difference in the timing of how I land and push off. maybe its not a constant speed thing. slowing and then accelerating to maintain the speed. That could also be saying I have one of those "putting on the breaks with my footstrike problems" but i dont think so. footstrike feels fluid and always forward moving but i imagine there's always some small changes in speeds during the landing and pushoff. the constant treadmill might force me to change the natural timing of the footstrike. who knows.
But yeah, given the cold weather, some blisters and slight cramping of running form probably are worth it.