Physics help - Simple Harmonic Motion.

[Llama]

Hi guys, need some help here.

We had a physics experiment in class. We made a pendulum by attaching both ends of a string to different points of a ruler and measuring the distance between them. (A weight hung between them obviously)

So now we're got a set of results, Time period (T) against distance (D)
Since the Time period of a pendulum in SHM is 2pi x ((root)l/g), is there an easy or quick way of finding l using the value of d?
I'm thinking maybe a relationship using logs (but I'm not very good at those, I know that the relationship between D and T wasn't linear) or some trig / pythag? Am I on the right lines or am I missing something here?

 

[No Limit]

I don't like these threads, they make me feel dumb.

 

[mindless_moder]

could you draw a diagram ? , it should be simple trig.

 

[Solaris]

What is L?

 

[ríomhaire]

What do you mean by distance? If it's oscillating the distance from the mass to the rest position should be changing with time. Do you mean the amplitude?

If you mean the amplitude do you mean the direct distance from the centre point to the maximum position or just the distance in the x (or y) direction? Even so the displacement of a pendulum is usually measured as a an angle so taking a distance seems strange.

What I'm getting at is please explain what distance you're looking for. The distance from what to what?

Hold on. I just read back over your post and I'm not sure I follow. You measured a string with a ruler and had a weight attacked in the middle? I'm even more confused.

Is this what you have?

If so the length is just the distance from the pivot to the centre of mass and you already have the period you say (and an equation relating them to boot!). So what's this distance you're looking for? Would the purpose of the experiment not be to just graph T versus sqrt(L)? Certainly 90% of physics experiments I've done are about producing graphs, I don't know how it is in other countries though.

 

[NeptuneUK]

I got 99 problems but the physics ain't one.

 

[KiplingsCat]

A diagram would be useful (and interesting); I've never heard of a pendulum being made in this way. Did you vary the distance between the two ends of the string; is that what you mean by D? In that case, l could be found if you knew the angles of the triangle formed by the perpendicular between the weight and the ruler and the piece of string. I assume the pendulum works in the same way as one that just goes straight down.

 

[Solaris]

He means a pendulum like this


\ --- /
\ -- /
\ - /
--O

 

[Dan]

simple trig:

L = 1/2 sqrt(D^2+S^2)

where S is the length of your piece of string

 

[MuToiD_MaN]

Dan won at math today, it would seem. Pythagorean Theorem solves all of society's ills.

 

[Dan]

actually Dan doesn't win. That + sign should be a - sign. Should be L=1/2sqrt(S^2-D^2)

 

[Maestro]

Funny enough we just started Simple Harmonics in my Physics course.

 

[dfc05]

Funny enough we just started Simple Harmonics in my Physics course.

Icky. That was my most hated part of physics (and I hated almost all of physucks). For some reason Simple Harmonic Oscillators have also come up in my non-physics classes in the past few weeks as some kind of mechanical analogy for atomic-scale electron stuff. I have no clue what's going on in class anymore. ;(

 

[ríomhaire]

Wow I can't believe I failed to understand the problem so badly. I feel pretty dumb.

 

[Mr. Djees]

Wait a minute, this doesn't sound simple at all!