UG Community @ Ultimate-Guitar.Com For all you physics experts out there..
 Register FAQ Members List Search Today's Posts
Search:

10-05-2012, 10:35 AM   #41
J-Dawg158
UG's Resident Dhampyr

Join Date: Nov 2008
Quote:
 Originally Posted by Arby911 Seems to me when the object leaves the starting point it's accelerating at -9.8 m/s^2 (or as the rest of us call that, decelerating). It then reaches apogee where it's at 0 m/s, and begins on its downward path at an acceleration of +9.8 m/s^2

Acceleration is a vector quantity( meaning it can be broken down into componants like left and right, or up and down, in other words, you can describe any 2 dimensional motion in terms of so far to the left/right and so far up/down.)

In physical terms, a change in sign means a change in direction. If the acceleration changed on the trip back down that would imply the now gravity is pulling you up instead of down.
__________________
I'm an
Engeneer
Enginear
Enginere

I'm Good at Math

10-05-2012, 10:44 AM   #42
Arby911
Finding the Pattern

Join Date: Jul 2010
Quote:
 Originally Posted by J-Dawg158 Acceleration is a vector quantity( meaning it can be broken down into componants like left and right, or up and down, in other words, you can describe any 2 dimensional motion in terms of so far to the left/right and so far up/down.) In physical terms, a change in sign means a change in direction. If the acceleration changed on the trip back down that would imply the now gravity is pulling you up instead of down.

Would it be correct to say that what I was describing above was the effect of acceleration, but not acceleration itself, and thus my error, or am I still not seeing it?
__________________
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin

10-05-2012, 10:55 AM   #43
ChaosInside
aspiring scientist

Join Date: Jul 2010
Location: Zanarkand
Quote:
 Originally Posted by Arby911 Would it be correct to say that what I was describing above was the effect of acceleration, but not acceleration itself, and thus my error, or am I still not seeing it?
Well, you were decently correct though. After it reaches 0 m/s it will accelerate downwards at 9.81 m/s^2. But since it is going in the -y direction it will accelerate at -9.81 m/s^2.

10-05-2012, 10:57 AM   #44
J-Dawg158
UG's Resident Dhampyr

Join Date: Nov 2008
Quote:
 Originally Posted by Arby911 Would it be correct to say that what I was describing above was the effect of acceleration, but not acceleration itself, and thus my error, or am I still not seeing it?

If you refer to it's effect on velocity, sure, but it's a little cumbersome. Essientially what you're trying to say is when velocity is positive and acceleration is negative then you decelerate (velocity is decreasing due to opposite directions), but when velocity and acceleration are both negative, it accelerates (velocity is increasing, but in negative direction.)

It's that whole rule of a negative times a negative equals a positive that causes this, but when it comes to physics if you don't pay attention to the direction(signs) then you open yourself up to many careless errors like inadvertantly adding two things that should have been subtracted.
__________________
I'm an
Engeneer
Enginear
Enginere

I'm Good at Math

10-05-2012, 11:02 AM   #45
Arby911
Finding the Pattern

Join Date: Jul 2010
Quote:
 Originally Posted by J-Dawg158 If you refer to it's effect on velocity, sure, but it's a little cumbersome. Essientially what you're trying to say is when velocity is positive and acceleration is negative then you decelerate (velocity is decreasing due to opposite directions), but when velocity and acceleration are both negative, it accelerates (velocity is increasing, but in negative direction.) It's that whole rule of a negative times a negative equals a positive that causes this, but when it comes to physics if you don't pay attention to the direction(signs) then you open yourself up to many careless errors like inadvertantly adding two things that should have been subtracted.

Quote:
 Originally Posted by ChaosInside Well, you were decently correct though. After it reaches 0 m/s it will accelerate downwards at 9.81 m/s^2. But since it is going in the -y direction it will accelerate at -9.81 m/s^2.

Great, thanks.

I've actually learned something useful in the Pit...not sure if I'm amazed or disappointed...
__________________
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin

 10-05-2012, 11:07 AM #46 J-Dawg158 UG's Resident Dhampyr     Join Date: Nov 2008 __________________ I'm an Engeneer Enginear Enginere I'm Good at Math
10-05-2012, 11:14 AM   #47
Arby911
Finding the Pattern

Join Date: Jul 2010
Quote:
 Originally Posted by J-Dawg158

I wonder if that 'The More You Know' campaign is the longest running PSA?

I know it's been around for a very long time, probably longer than most of the residents here...
__________________
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin

 10-05-2012, 12:49 PM #48 MAC2322 UG's Twilight Sparkle     Join Date: Feb 2009 Location: Bogotá, Colombia. Perhaps a better way to think about it is in terms of direction rather than positive and negative. Rather than thinking of negative acceleration as 'slowing down', we think of it as 'accelerating downwards'. Going by this definition, if you're traveling upwards but accelerating downwards, then yes, your speed is going to decrease, but once you turn around, you're still accelerating downwards, so you speed up. The speed graph I drew earlier reflects this, with the speed going down and then back up as it changes direction. The velocity graph actually shows the exact same thing, only that, after t1, it's going higher in the negative direction. I suppose the final idea is that the negative sign is an indicator of direction rather than actually meaning 'less than 0'. __________________ My signature lacks content. It is, however, blue.
10-05-2012, 01:10 PM   #49
oneblackened

Join Date: Oct 2007
Quote:
 Originally Posted by Colgate Total Velocity is the speed; acceleration is the rate at which is speeds up or down.

not QUITE right. Velocity is speed in a direction and acceleration is the rate at which velocity changes. This is why something going in a circle is always accelerating even it's moving at the same speed.

OP: Acceleration.
__________________
Current Gear:
LTD MH-400 (Dimarzio D-Activators)
LTD MH-400NT (BKP Nailbomb/VHII)
ESP Horizon NT-7 (SD Full Shreds)
UA Apollo Twin Duo
Peavey Revalver 4

I'm a recording engineer. If you have questions or you want some work done, message me.

 10-05-2012, 01:12 PM #50 lncognito Registered User   Join Date: Dec 2011 It's rather astonishing how long this thread for a rather basic physics-question has been going...
10-05-2012, 01:48 PM   #51
Arby911
Finding the Pattern

Join Date: Jul 2010
Quote:
 Originally Posted by oneblackened OP: Acceleration.

You sure? Seems several folks above disagree?
__________________
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin

 10-05-2012, 02:10 PM #52 justinb904 Mother F***ing Engines     Join Date: Dec 2007 Location: The Middle of Nowhere, New Mexico This thread has made me realize just how much calculus and physics I've forgotten. It's a little sad __________________ Warning: The above post may contain lethal levels of radiation, sharp objects and sexiness. ☢ Proceed with extreme caution! ☢
10-05-2012, 02:11 PM   #53
Arby911
Finding the Pattern

Join Date: Jul 2010
Quote:
 Originally Posted by magnus_maximus It's velocity, for crying out loud. I'm a third year physics student, listen to me.

I'm not arguing the point, I'm asking oneblackened if he/she/it is sure?

And I'm a left-handed insomniac twice removed on my mother's side...unprovable credentials mean shit on the internet...
__________________
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin

10-05-2012, 02:27 PM   #54
J-Dawg158
UG's Resident Dhampyr

Join Date: Nov 2008
Quote:
 Originally Posted by MAC2322 Forgive the red marker, I'm all out of other colors. Anyway, as you can see from the graphs, Velocity is the only quantity whose sign changes. I avoided using dx/dt and dv/dt for velocity and acceleration respectively since I doubt your Physics class is Calculus-based, but for those of you who do know Calc I, derivatives are what I was approximating with my Δy/Δt and Δv/Δt. I also marked the time t1 at which the object reaches its highest point so you could see how different quantities are changing (or not changing) at that time.

This↑↑↑
__________________
I'm an
Engeneer
Enginear
Enginere

I'm Good at Math

 10-05-2012, 03:59 PM #55 kertets Banned     Join Date: Jan 2012 Location: On the toilet. Just leave the feckin ball where it is and eat something. Last edited by kertets : 10-05-2012 at 04:01 PM. Reason: dont like this ******
 10-05-2012, 04:24 PM #56 kalnoky7 Bland     Join Date: Nov 2007 Location: A place of settlement, activity, or residence Only velocity... position changes within the range of 0 and max distance (which is postivie) velocity starts out upward, shrinks, becomes null at max height, and augments negatively (downard vector) acceleration is always downward, by which I mean gravity, so contrary to the starting motion and negative at all times... Was an expert really needed for this?
10-05-2012, 04:27 PM   #57
British_Steal
UG Member

Join Date: Aug 2007
Location: Up here in space Im looking down on you My lasers trace Everything you do
Quote:
 Originally Posted by Metallica1554 The answer is velocity because it is a vector quantity, hence speed and direction are taken into account. The direction that the ball is travelling in changes throughout the flight, so on the way back down the velocity becomes negative.

well done well done.
__________________
Quote:
 Originally Posted by The Spoon Unless you're sure she likes you, telling her you like her has a 110% chance of failing. But hey, at least you have a 10% chance of absolutely guaranteeing failure.

 10-05-2012, 04:29 PM #58 kalnoky7 Bland     Join Date: Nov 2007 Location: A place of settlement, activity, or residence ^ acceleration is also a vector quantity, it's just unchanged in this case (assuming there's no wind resistance) edit: even wind resistance would not invert the accel. sign, just diminish or increase it's value a bit Last edited by kalnoky7 : 10-05-2012 at 04:31 PM.

 Thread Tools Rate This Thread Rate This Thread: 5 : Excellent 4 : Good 3 : Average 2 : Bad 1 : Terrible

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off
 Forum Jump Please select one User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home -------------------- UG Community     New Members Q&A Forum     The Pit     Archives Of The Best Threads         Music Theory Archives         Technique Archives         Bands & Artists Archives         Electric Guitar Archives         Bass Archives         Songwriting & Lyrics Archives         Bandleading Archives         Community Archives Music     Bands & Artists         Rock & Indie         Hardcore & Punk         Blues, Jazz & Other Guitar Styles         Metal         Other     Songwriting & Lyrics         Songwriting & Lyrics Contests         Songwriting & Lyrics Techniques     Recording         Tabs & Chords         Recording Contests         Original Recordings         Cover Songs     Tab Talk     Musician Talk         Bandleading         Singing & Vocals     Promote YOUR Band     Classifieds         Musician Ads         Gear Ads Instruments     Guitar Techniques     Acoustic & Classical Guitar     Electric Guitar     Bass Guitar     Guitar Gear & Accessories     Gear Building & Customizing     Drums Misc     Ultimate Guitar Feedback         Site Suggestions         Mobile Apps Feedback         Tab Pro Service Feedback         Bug Reports     UG Contribution

All times are GMT -4. The time now is 05:46 AM.

 -- UG Black Style -- UG Classic Style
Forum Archives / About / TOS / Advertise with us / Customer Support / Ultimate-Guitar.Com © 2016