Log In

Sorry, I was ambiguous -- there's two different things called "system" in discussion here: the system of moving objects, and the system of equations describing them.

In each equation, t is how long the object has been in motion.

Solving the equations together as a system means that you're looking for the value of t that makes the two equations coincide. To be rigorous you should use a subscripted variable like t_1 like I had mentioned to represent that you're looking for a specific time. (By convention, t_0 would be the time at which you start watching, and for these simple exercises you choose your timeline so that t_0 = 0 to make the math easier.)

Similarly, I was using v for velocity, and rigorously speaking I should have been using v_0 because that represents the INITIAL velocity of the ball, because the velocity changes over time. But in practice you don't have to be that rigorous in your notation as long as everyone involved understands what you're talking about -- but this time, that wasn't true, so I needed to be clearer.

Ohh okay, that makes sense! In other words, if the stuff was already accelerating, the t when they ball and the platform coincide would be even longer, and the t from the moment the ball fell to the moment the ...do you mean to find the velocity, first one needs to use some other time, then later plug the velocity into the ball equation and then the t when the two equal each other is the time they coincide?

Ball: y = 10 + v*t - (1/2)g*t^2
Platform: y = 0 + (1/2)a*t^2

No, the equation only cares about the initial velocity. The acceleration term provides the information necessary to handle the change over time.

Actually FINDING the velocity at a given time is a completely different thing. In calculus, you would determine this by using the first derivative (which is why there's the 1/2 factor), but at this level, you just have a different equation to work with.

The equation for the position of an accelerating object generalizes to this form:
s = (1/2)a*t^2 + (v_0)t + s_0
where:
s is the position at time t
a is the acceleration
v_0 is the initial velocity
s_0 is the initial position

You can find how fast the object is going at any time using this equation:
v = a*t + v_0

The fun part of having all of these equations available to you is that they're all tools that can build up more solutions. Knowing this equation, you could figure out what the acceleration is for an object if you know how fast it's going at two different points in time (because then you would have v, t, and v_0 defined and solve for a) and then you could plug that back into the position equation to figure out where the object is at any point in time, past or future.

By the way, folks, this thread doesn't have to be dedicated to Potironette. I'm happy to help anyone else who needs it.

Can I quote Coda and put it in the first post XD?
And thanks a lot Coda! It makes a lot more sense/seems simpler now!

Naturally, you're welcome to!

And you're also welcome for the help. :)

...assignment...done...fourteen...hours...yay.

If anyone wants to know anything about MARC 21 cataloging records...no. Done.


Is this a math thread? I don't math. I English though. I English enough to have opinions on "literally," the Oxford comma, and the presence of imaginary or creative states in the poems of John Keats.

It's not limited to math. I also do science and technology (including computer programming), and I English really good too. (That last phrase was calculated to generate as much cringe as possible.) I used to hang out on r/askscience answering questions there.

Anyone else who wants to contribute skills to the thread is welcome to!

English, I'm not good at, at all. Whenever I write essays I get lots of points off for awkward sentences and bad grammar D:.

Random questions:
When I write about possession, do I write "Columbus' ships" or "Columbus's ships"?

...What's MARC 21?

If you have spare cash, pick up the book "Eats, Shoots & Leaves." Wonderful book, and funny. All about grammar. My specialty is literature over language but I can function well enough.

I believe that case is simply the version of English you are using. British English uses "Columbus' ships" and American English is typically with the repeated s. It doesn't hurt to ask your teacher what they might prefer. I usually don't use the extra s but I usually lean towards British English. Canadian English is generally a mix of the two, and I've seen both.


MARC 21 is the coding language for library catalogues, or that's the easiest way to think of it, for me. It's a record set that the computer reads to display what you would see in a library catalogue entry. Looks like this.


...edited for bad typing.

The MARC 21 picture looks really interesting (and confusing), though whatever Rose, Hudgins, Macmillan, and Conway are sure must be important :o.

Ohh, no wonder I see different ones all the time. I think my teachers grade them all correct, so long as we're consistent.
Thanks!

This title is funny XD! At first I thought this was about eating bamboo shoots. Then I realized it might be about shooting and tree leaves. After that I realized shoots and leaves might also mean firing guns and parting X'D

That's the point of the title, heh. It's horribly unclear what it's supposed to be.

I actually punctuated the title incorrectly, and fixed it in my post edit, but yes, that's the point. Good book. :)

"The Oatmeal" is also a good blog (if inappropriate at times) for illustrated, silly examples of how to use certain words and punctuation in its grammar section, like this one on how to use a semi-colon. I forget those details constantly.

Lol XD. I remember that exact webpage of the Oatmeal when I was struggling to figure out how to use a semi-colon. Sadly, today I still have problems understanding the semi-colon. I can't tell what a clause is; I can't even tell what a regular sentence should include except by feeling...is that even proper semi-colon use XD?

Honestly, I'm not sure. Grammar is not my strong point. I passed it all by instinct and feel. After looking it up, a "clause" appears to be a single thing a sentence is about.

I break things down into basic language when I can. I find it helps with understanding. At its most basic, a sentence should have two parts: a thing (subject), and something about that thing (predicate).

"I (the thing) have a dog (something about the thing)."

"He (the thing) pooped (something about the thing)."

At its most basic, that makes up a complete sentence.

Each of those sentences has one clause.

"I have a dog." = one clause.
"He tried to eat me." = also one clause.
"I have a dog and he tried to eat me." = two clauses, separated by "and."

According to that poster, you can use a semi-colon in place of that "and" to separate those two clauses:

"I have a dog; he tried to eat me."

This is how I teach myself these things. It's sort of the extreme of "back to basics."

I should think through my posts more so I don't end up editing them so much.