Easier to walk upstairs, but why is it harder to walk down?

[xoops]

Hi all,

This questions is bothering me lately. Why is it easier to walk down the stairs, than up the stairs?

I'm clueless, any help greatly appreciated.

Thanks,
Matt

 

[Tide]

It's the same reason why your arms get tired when you have them extended while holding weights. You aren't doing any work on the weight (F dx = 0) but you are doing "biological work" since your heart exerts a force to push blood through your veins. That requires energy.

You do more biological work going up stairs than you do when going down.

 

[Manchot]

We don't "spend" energy to brake, we simply turn our kinetic energy into thermal energy when we collide with the staircase.

 

[xoops]

I know everything finally converts to thermal energy... hmmmh, but I'm not yet convinced about non-breaking.

do you think there is a way to do some measurement by amateur? I have altimeter and thermometer on my hand watch.

 

[Tide]

I know everything finally converts to thermal energy... hmmmh, but I'm not yet convinced about non-breaking.

do you think there is a way to do some measurement by amateur? I have altimeter and thermometer on my hand watch.

I think you'll need more than that. You'll need at least a pulse monitor and some means to measure oxygen intake and carbon dioxide output.

 

[xoops]

Ok, I'll arrange it. Can you please explain how'd I try this experiment?

Many Thanks

 

[xoops]

..or atleast an equation to calculate it.

 

[russ_watters]

We don't "spend" energy to brake, we simply turn our kinetic energy into thermal energy when we collide with the staircase.

You most certainly do expend energy when braking. Any time your muscles are in use, for any purpose, they require energy - and roughly the same energy regardless of whether expanding or contracting, as long as the force being exerted is the same. There are weightlifting techniques designed to maximize that and most trainers will tell you that the way you lower the weight down (slow, controlled) is more important than the way you raise it up. There are even "weightlifting" techniques where you don't even move! (isometrics)

Ok, I'll arrange it. Can you please explain how'd I try this experiment?

A few suggestions:

-Use a high enough staircase that it takes at least a minute to go up or down.
-Try to keep the same pace going up and down.

"Up" case:
1. Measure your heart rate
2. Go up the stairs (time yourself)
3. Measure your heart rate

[long pause between the two]

"Down" case:
1. Measure your heart rate
2. Go down the stairs (time yourself)
3. Measure your heart rate

If you work or go to school in a place with a good candidate stairwell, you may be able to work this into your day without looking too strange to people around you. Ie, when it's lunch time, measure your heart rate at your desk, then get up and walk down the stairs, stop and measure your heart rate at the bottom. After lunch, if you are walking from somewhere and your heart rate is up a little, sit at the bottom of the stairs (in a lobby or something) until it drops to normal, then walk up the stairs.

 

[Homer Simpson]

force = mass x acceleration
Work = force x distance

Like Russ is saying: If you descend extremely slow and controlled there will be much less difference in the upward force required.

Think of an elevator. The tension in the cable is constant while the elevator is moving in either direction (equal to mass of elevator * g) Only when the elevator begins to accelerate up or down from a stopped position does the tension change.

So you have to apply work to go up the stairs. Its the force to overcome gravity x the distance you do this for. However going downstairs you can cheat the workload. Consider just hopping down stair to stair with locked legs. No work is being done here at the muscle level. Its just the impact force with your feet bottoms that does the ‘braking’

 

[russ_watters]

That's true - because of the position of your limbs, a fair amount of the impact is absorbed via the shock of the impact. But I suspect your muscles absorb more than you realize and if you actually try top hop with a locked-knee, you'd hurt yourself.

 

[DocToxyn]

You most certainly do expend energy when braking. Any time your muscles are in use, for any purpose, they require energy - and roughly the same energy regardless of whether expanding or contracting, as long as the force being exerted is the same.

While I agree that work is being done regardless of going up or down, I need to clarify that muscles only work in one direction. Muscles are contractile only and thus can only pull, they work in pairs to effect body motion like lifting an arm or walking up or down stairs.

 

[skywolf]

the real question would be which one is easier, going up then down
or going down then up?

i would say that going up then down would be easier because the gravity is less higher up