THE 10,000 Post Thread

[Vahr 341]

1381

The thing is, each type of explan has its own place. If you're speaking to a person who is developing a 3D Physics engine, you'll want to go with the first one. Now if you're teaching 4th grade students about mass, then you go for the second one.

And if you're teaching college students, you explain it like this: "You have 2 bottles of beer on one side of a 2x4 on a barrel. You would need 2 on the other side, if the barrel is in the center."

EDIT: Oh no. Looks like the PFB has manifested itself.

[Larks2242 251]

1382. What does that all mean?

[Duke87 1,070]

(1383)

Think lever action. You apply a force to the end of a lever.

You create a torque (moment) by doing this. M = Fx

Well, with two forces, you can create a balance:

In order for this "seesaw" to not move, the moment from the left and the moment from the right must be equal.

Or, F₁x₁ = F₂x₂.

  Three or more forces, same idea.

F₁x₁ = F₂x₂ + F₃x₃.

You just need to follow a sign convention (this is better expressed as -F₁x₁ + F₂x₂ + F₃x₃ =0).

The forces need not all be acting in the same direction:

F₁x₁ = F₂x₂, as before.

The same physics still apply even if you have more than one support. For instance, in that last example, F₂ can be the reaction of a support at the end there.

The only part of the picture missing, then, is the fact that the fulcum itself hosts a reaction. So, this:

can also be represented like this:

As per static equilibrium:

ΣF_x=0

ΣF_y=0

ΣM_A=0

Very simple. It's just elementary structural physics.

[astronelson 339]

1384. You're not telling me anything that isn't intuitively obvious, Duke.

[Larks2242 251]

1385. Ok i think i will leave the math to you Duke, you obviously know what your doing

[Duke87 1,070]

(1386)

Originally posted by: astronelson

You're not telling me anything that isn't intuitively obvious, Duke.quote>

Okay then, pop quiz:

A_x = ?

A_y = ?

B_y = ?

[Deathtoall 28]

1387. *Looks above, keeps on walking past*

[GlobexCo 33]

Originally posted by: Duke87

(1386)

Originally posted by: astronelson

You're not telling me anything that isn't intuitively obvious, Duke.quote>

Okay then, pop quiz:

A_x = ?

A_y = ?

B_y = ?

quote>

1388 It should be:

A_x = is it possible?

A_y = ~13,3 kN

B_y = ~6,6 kN

[Larks2242 251]

1389. Ask Duke

[Korot 6]

1390. Without a turning point given, it is impossible to calculate the proper forces.

[Vahr 341]

1391

I think the two fulcrums (and I think its possible to have 2) are highlighted in blue.

From Duke87:

"The same physics still apply even if you have more than one support. For instance, in that last example, F2 can be the reaction of a support at the end there."

(I'm too lazy to use the quote function )

So then go ahead and calc from there. And you don't always need to use a catch-all equation for basic levers. Setting up a proportion works well enough for basic levers.

[Duke87 1,070]

(1392)

Globex: all wrong. And I can tell what mistake you're making.

Korot: the "turning points" aren't given, silly. You need to select them!

BL: The blue arrows represent forces being applied. They are not meant to indicate fulcra.

I'll post the proper work and answers once astro gets back to us...

[Korot 6]

1393. However, if I do that, the requested forces also change in size.

[GlobexCo 33]

1394 ... I used my imagination ...

[un1 41]

1395 - I'm to tired to do math today.

[Duke87 1,070]

(1396)

Originally posted by: Korot

However, if I do that, the requested forces also change in size.quote>

You must be doing something wrong, because no, they don't.

[Vahr 341]

1397

So who got snow? Cause I haven't. Its OHIO in DECEMBER. And we have sun and clear skies.

[Korot 6]

1398. ^ Anyone else needing proof of climate change?

And Duke, that statement was mainly a guess, one that seemed most logical to me. Think of a see-saw, which is 10m in length and has a mass that can be estimated as being 0 kg. Imagine the turning point to be right in the centre of it, and a 10kg weight on each side. Now, what happens when you move the turning point 2,5m to the right? Correct, the see-saw topples clockwise, until the left side touches the ground. If we don't want this to happen though, we'd need to increase the weight on the right end with a factor of 3, and thus alter the force applied to that end.

[GlobexCo 33]

Originally posted by: Blue Lightning

1397

So who got snow? Cause I haven't. Its OHIO in DECEMBER. And we have sun and clear skies.

quote>

1399 Last year school closed here because of snow. This year we're still waiting for snow...

[Hamish 1,369]

1400. I think I remember changing the numbers on the page that was destroyed by the timestamp issue. So I think they are all done now.

[Vahr 341]

1401

Yay, so we're officially back on track!

Globex: We've closed school I think 3 times last winter. I think one of them was in the week after Thanksgiving...

[un1 41]

1402 - Thats good to know.

[Duke87 1,070]

(1403)

Originally posted by: Korot

that statement was mainly a guess, one that seemed most logical to me. Think of a see-saw, which is 10m in length and has a mass that can be estimated as being 0 kg. Imagine the turning point to be right in the centre of it, and a 10kg weight on each side. Now, what happens when you move the turning point 2,5m to the right? Correct, the see-saw topples clockwise, until the left side touches the ground. If we don't want this to happen though, we'd need to increase the weight on the right end with a factor of 3, and thus alter the force applied to that end.quote>

Okay, but I'm not talking about moving any supports. I'm merely talking about moving where you choose to sum the moments about. If the system is in equilibrium, than every part of the system must be in equilibrium. If the sum of the moments about the fulcrum is zero, the same must be true for the sum of the moments about any point.

Besides, this isn't a seesaw. It's a stable structure with three reactions. You can put any magnitude of force on it anywhere and it won't move except for deformation due to stress (unless it breaks).

[Larks2242 251]

1,404. So anybody wana talk about something that does not include math

[Chptrk 86]

1,405. Well, we could talk about how totally adorable anyone with cat ears and a tail put on them look!! I'm squeeing just thinking about them!! Kittys!

[Hamish 1,369]

1406. But that would be lying... lol kidding Chptrk, Kittys are cute.

[Larks2242 251]

1407. Cool christmas avatar Hamish looks just like your old one

[Keegan V50 15]

1408. Wow most of you guys have changed your avatars lol

[Deathtoall 28]

1409, i was pushed into this post

[Larks2242 251]

1410.@ VV Yep just in time for the holidays