/sci/ - Science & Math

can anyone help me?

No homework threads. Chemo away.

>>1391451

fuck no, I just thought it might be interesting to try to calculate a "walking equation" with respect to time

In that case, carry on.

>>1391436
The angle of your foot may be changing, but the direction of frictional force is constant.

>>1391476
I would think that when you put your foot down it points back and then switches forward as you "pull" yourself forward.

>>1391476
but the magnitude of the friction force varies with the the angle from the equation mgsinΘ

>>1391509
That's only on an incline. Note: accoding to the standard highschool model, fritctional force varies with the normal force, on a level surface: mg.

I got as far as mg⌠sin(dΘ/dt) , I just have no idea how to calculate sin(dΘ/dt)

>>1391501
Maybe for a split second, fine, but its a negligible effect I think.

>>1391517
Of course, the normal force is lower as you are accelerating down and higher as you push up. Angle has very little to do with it.

>>1391522
What does sin(d(theta)/dt) represent to you? I'm not sure, but I don't think you need the differential. I do'nt know exactly what you want.

I hope I at least have the right idea about how I'm going about this problem

>>1391532
well, I assume that the angle changes with time, therefore dΘ/dt, right?

didn't he integrate incorrectly anyway?

>>1391546
What are you trying to get? The change in force with time?

In that case, the correct method would be to find the force for any angle, and then take the derivative. What you're doing is finding something relative to the rate of change in the angle, which is not what you're looking for. Your final equation should not have a d(theta)/dt in it.

>>1391557
so what formula should I be arriving at? also, what formula would have dΘ/dt in it?

>>1391583
Actually, there's more than one way to look at this.

What you want to do is write down the equation for force. Then, to find the equation for the rate of change of force with time, you simply replace theta with d(theta)/dt, so I suppose that's correct. Why you're integrating i'm not sure.

Sorry if I'm confusing you, its late and its hard to explain this in text.

>>1391611
thanks for trying to explain it, I thought by integrating the formula, you could have an equation that could tell you the angle at any time t ( it seems I was going one step to far if I'm understanding you correctly)

>>1391611
integrating arrives at velocity doesn't it? (mg is an acceleration after all)
I'm just saying this because i'm confused as fuck about what hes even asking haha.
that also seems like some fucked up chain rule, shouldn't this bad boy switch to cosine?
i'm stoned and can't focus tonight so if i'm just derailing sorry.

Θ_Θ

>>1391632
well yeah, I can get to -cos(dΘ/dt) but had no idea of how to integrate the dΘ/dt part

>>1391476
Not even a little bit. Think about which direction your feet slip if you try to walk with a normal gait on ice. When you put your forward foot forward, it slips forward until you shift your weight over it. Then your feet slip out to the sides as you're shifting weight from the leading to the trailing foot. Then your trailing foot slips out from behind you as you shift your weight onto it.

The direction of frictional force has components in the x and y directions (forward-back, side-side) and changes through a whole range as you step.

Here's just a rough guess about the approximate direction and magnitude of the friction vectors in a stride. The time/force graph is only for one foot. The other foot would obviously be half a phase off. It's not quite a true sine function since there's a discontinuity when you pick up your foot to take a step.

>>1391632
yeah, this was in a moment of nerdiness, so I apologize if my assumptions/methods about this problem are incorrect, and would appreciate if some /sci/duck could correct me

shameless self bump

>>1391517
what this guy said. you're making it much more difficult than it is. although the angle of your foot changes, the force of gravity is still being applied straight downward on a level surface so there is no theta. as your foot comes down, the thing that will change from time is the location of the normal force (or resultant)

>>1391654
<span class="math">\int \frac{d\theta }{dt}= \theta + c[/spoiler]
where c is your initial condition, which is unnecessary in this case.

>>1391718
huh, I was under the impression that you needed some angle Θ with respect to the ground to be able to propel ( for lack of a better word) yourself forward. Am I incorrect?

>>1391757
well in reality, this is nothing close to what walking is actually like but i'm trying to keep it simplistic. walking is actually more of a controlled fall.

>>1391748
That is what I originally thought as well, but what happens to the time in the equation, it needs to be in the equation somehow, right?

>>1391764
hmmm, never heard it described that way before, could you elaborate?

>>1391793
if this article sucks let me know, haven't had tiem to read it
http://discovermagazine.com/2001/jul/featphysics
just googled "physics of walking"

>>1391814
huh, this makes sense, thanks for the link, night yall