For the biomechanics or physiologists...

[Brian Ashton]

So! I've been thinking about this one for a while...

If a person walks a mile and then runs that very same mile, and everything else being equal, does that person use up the same amount of joules (calories) for walking and running.

Logic tells me the work needed to travel the distance is equal and therefore the energy used should be the same... But for some reason I suspect there may be more energy burned running. But I don't know where or why.

What say you.

[John Coloccia]

I didn't stay at a Holiday Inn express, but I do know a bit about physics. I'd guess that running is less efficient, mostly due to enormous amounts of energy lost to impact and poor form required to absorb the impact and generate large forces to recover. I would suspect that if you put big, efficient springs on the bottom of your shoes to lessen the impact energy lost, the efficiency would go way up because less energy would be lost and better form could be used.

[Chuck Wintle]

in my opinion it takes more energy to run a mile vs walking that same mile. Why? Because everything else being equal its the time factor. the more quickly you move a certain mass a given distance the more energy is required. Goes that seem right?

[Dan Hintz]

Running will require more energy... not because you get there faster, but because the movement is more grand in scale than walking. Consider the typical gait of a walk... your body may rise/fall a few inches from step to step. When running, you tend to bound upwards more with each stride, which requires more energy (you're working agianst gravity). You cover the same linear distance (the mile), but your body covers a much longer path along the way.

You'll also feel more tired when running because you're asking your muscles to expend energy in a shorter amoiunt of time... as lactic acid builds up, you feel like more energy was expended. By walking, you're giving your body a chance ot keep the lactic acid level very low.

[Chuck Wintle]

Running will require more energy... not because you get there faster, but because the movement is more grand in scale than walking. Consider the typical gait of a walk... your body may rise/fall a few inches from step to step. When running, you tend to bound upwards more with each stride, which requires more energy (you're working agianst gravity). You cover the same linear distance (the mile), but your body covers a much longer path along the way.

You'll also feel more tired when running because you're asking your muscles to expend energy in a shorter amoiunt of time... as lactic acid builds up, you feel like more energy was expended. By walking, you're giving your body a chance ot keep the lactic acid level very low.
Dan,

assuming this was a mass being moved a mile and since time elapsed becomes a function of acceleration then would it not be logical that more energy is required to overcome inertia quickly as opposed to simply going very slowly?

[Glenn Clabo]

The answer is yes it's more complex than seems and continues to be studied...
http://www.runningplanet.com/training/running-versus-walking.html

(http://www.runningplanet.com/training/running-versus-walking.html)

[Jason Roehl]

This is why I cycle. :D

[Brian Ashton]

The answer is yes it's more complex than seems and continues to be studied...
http://www.runningplanet.com/training/running-versus-walking.html

(http://www.runningplanet.com/training/running-versus-walking.html)

Excellent find - thx mate!

[Dan Friedrichs]

Actually, no WORK is done to move an object horizontally. Work is only performed upon an object if you move it vertically, because you increase (or decrease) the object's potential energy.

[Tom Winship]

Actually, no WORK is done to move an object horizontally. Work is only performed upon an object if you move it vertically, because you increase (or decrease) the object's potential energy.

Dan, what you say is true if you neglect friction, correct? It does take work to move a pallet with 1000 lb. weight across a sidewalk.

[Bob Chapman]

This question was just answered on CNN.com under "Diet & Fitness". Check it out.

[Dan Hintz]

Dan,

assuming this was a mass being moved a mile and since time elapsed becomes a function of acceleration then would it not be logical that more energy is required to overcome inertia quickly as opposed to simply going very slowly?
You can't neglect friction, so you also have to include deceleration on each step. If, however, this was on a frictionless surface and in a vacuum, the energy spent accelerating lightly over the first half of time would be equal to the time spent decelerating over the other half of time. Or you could exert a really quick burst of energy over 10% of the time to get it moving, then a really quick burst over the last 10% of the time to stop it... either way, the total energy spent will be equivalent.

Though to be fair, it's been a loooong time since I even thought about such things, so I'd have to crack open the physics book to make sure I'm still barking up the right tree. F=ma, so you impart a force upon that object to get it moving. However, as you push it harder, you don't have to push as long to get it moving at the same velocity. Therefore, energy is conserved, i.e. the energy spent pushing the object slowly but over a long distance is the same as pushing it more quickly but over a shorter distance. Once you jump off of one foot while jogging, the energy burst was spent getting you up and moving... jog faster (spend more energy in each step), and that increase in energy sends you a longer distance before your next foot touches the ground.

[John Coloccia]

If it were frictionless, you couldn't accelerate or decelerate. :)

OK, I'm being persnickety, but that's the problem with analyzing situations like this sometimes. It's possible to idealize too much and get left with an answer that doesn't really work anymore. As soon as you have a real situation that can actually work, you quickly find that you need to consider the efficiency of the various processes in order to get to a real answer, and that requires analyzing the real mess of a real situation.

But as a thought experiment where everything is equally efficient (no need to invoke a frictionless surface), you can certainly expend varying amounts of energy. For example, if we're playing pool and I want to roll a ball from one end of the table, into a cushion and then catch it coming back, I could roll the ball very lightly (expending a small amount of energy) and catch it very gently (expending little energy) or roll it very hard (expending a lot of energy) and catch it aggressively (expending a lot of energy to slow it down). All of this energy that we put in will eventually get converted into other forms as the ball comes to a stop (heat, chemical energy from processes in your body, etc).

But now when we consider the efficiency of rolling a ball and catching it, we will find that there is certainly a most efficient manner of doing it. Let's pretend that we need to throw and catch all 15 balls (the equivalent of taking steps). There is a most efficient way to move your body that will optimize the speed of the balls, the movement of your arms, wrists etc, the catching of the balls coming back (for example, allowing the momentum of the ball being caught to help move your arm back into the "ready" position to throw another ball), etc etc. The most efficient way to do it is probably not to throw them very hard, like running, because you loose a lot of energy to impacts and get nothing in return. In fact, if you throw too hard, you waste energy accelerating the ball, and then you waste it again decelerating the ball that's now going far too fast. It's also probably not to thrown them as lightly as possible because you're not making good use of body mechanics. It's probably somewhere in between.

Anyhow, Einstein was the master of the thought experiment, but leaving out too many details tripped him up too. If you're interested, check out Einstein's Box and the debate between Bohr and Einstein. One of Bohr's greatest triumphs was figuring out where Einstein idealized just a touch too much :)

[Dan Hintz]

If it were frictionless, you couldn't accelerate or decelerate. :)
What, you've never heard of the ACME rocket pack?! Friction not necessary (and in fact, frictionless is preferred).

[Bruce Volden]

You guys, you are sooo over my head!! BUT, I can certainly tell you that as I age;

1) Time goes faster

2) Gravity is stronger---'nuff said.

Bruce