vector uderstanding

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#1
Hi,

Im new to vectors and i am confused about the notation. Say you wanted to graphially represent a vector in two dimensional space i get that you can use a directed line segment and we can denote this as PQ with an arrow above. Am i right in saying that the points P and Q have no relevance unless you are dealing with displacement vectors?
Last edited by hiyatt; 2 years ago
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2 years ago
#2
Since vector PQ (with the arrow on top pointing right) is found by vector q subtract vector p, then positions P & Q would surely have some relevance!
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#3
(Original post by begbie68)
Since vector PQ (with the arrow on top pointing right) is found by vector q subtract vector p, then positions P & Q would surely have some relevance!
the PQ notation is only useful when you care about the endpoints, for velocity vectors you don't care about the endpoints. Where did you get p and q from, P and Q represent points and together with the arrow on top represent a vector.
Last edited by hiyatt; 2 years ago
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2 years ago
#4
(Original post by hiyatt)
Hi,

Im new to vectors and i am confused about the notation. Say you wanted to graphially represent a vector in two dimensional space i get that you can use a directed line segment and we can denote this as PQ with an arrow above. Am i right in saying that the points P and Q have no relevance unless you are dealing with displacement vectors?

By the way how old are u???
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#5
(Original post by humble.boy)

By the way how old are u???
Thanks, but my question was regarding dropping the endpoints completely and referring to the vector as just b
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2 years ago
#6
p usually denotes position vector of P. ie OP
same for the q vector.

ok, so you're dealing with SUVAT vectors.
Then yes. P & Q are relevant in displacement.

But they can also be used in certain situations with a velocity and/or acceleration equations, since SUVAT eqns can involve all 3 (s, v & a), of course ....
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#7
(Original post by humble.boy)

By the way how old are u???
15
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2 years ago
#8
(Original post by hiyatt)
Thanks, but my question was regarding dropping the endpoints completely and referring to the vector as just b
then that's fine, but I think it's difficult to then say that b is completely independent of P & Q, since it's the difference (or journey) between those 2 points from which you derived/calculated the vector b in the first place!
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#9
(Original post by begbie68)
then that's fine, but I think it's difficult to then say that b is completely independent of P & Q, since it's the difference (or journey) between those 2 points from which you derived/calculated the vector b in the first place!
there's no calculations going on anywhere i have literally opened the first page of my book on vectors lool
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#10
(Original post by begbie68)
then that's fine, but I think it's difficult to then say that b is completely independent of P & Q, since it's the difference (or journey) between those 2 points from which you derived/calculated the vector b in the first place!
Thanks for you help
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#11
(Original post by hiyatt)
15
joking im actually 20
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2 years ago
#12
(Original post by hiyatt)
Thanks, but my question was regarding dropping the endpoints completely and referring to the vector as just b
I did not understand what u said.....
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#13
(Original post by humble.boy)
I did not understand what u said.....
Thanks for your help but right now that looks like a load of symbols to me with no meaniing. i was talking in a more general sense about whether the PQ notation was useful when talking about velocity vectors. I dont believe it is actually used for velocity anyway. But my question was purely notational.
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2 years ago
#14
(Original post by hiyatt)
joking im actually 20
20.....You don't know vector yet???I've heard UK study system is quite difficult.....I'm from india...Here I read vector when I was 12 or13....
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#15
(Original post by humble.boy)
20.....You don't know vector yet???I've heard UK study system is quite difficult.....I'm from india...Here I read vector when I was 12 or13....
Na i just skipped that chapter in my a levels
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2 years ago
#16
(Original post by hiyatt)
there's no calculations going on anywhere i have literally opened the first page of my book on vectors lool
What's the book?

As I understand it, you're just starting a maths degree. In my experience, one thing books/lecturers tend to go on about a fair bit (if you're being introduced to vectors at university level) is how/whether what you're doing depends on your choice of coordinates.

In particular, if you have points P, Q, and you define vectors p, q to be OP, OQ, respectively, then your vectors depend on where you've decided to put the origin. But the vector PQ (= q - p) does NOT depend on your choice of origin.

If this is what's going on with you, I have to say that I think they spend too much time/emphasis on this at a time when you're just getting used to the concepts. And so to a large extent I'd say don't worry too much about it - you should be able to pick a lot of it up "by osmosis", and in further lectures you'll probably find you don't need to worry that much (in that you will always be dealing with the form v = (x, y, z) where all you really care about are the values of x, y, and z).
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#17
(Original post by DFranklin)
What's the book?

As I understand it, you're just starting a maths degree. In my experience, one thing books/lecturers tend to go on about a fair bit (if you're being introduced to vectors at university level) is how/whether what you're doing depends on your choice of coordinates.

In particular, if you have points P, Q, and you define vectors p, q to be OP, OQ, respectively, then your vectors depend on where you've decided to put the origin. But the vector PQ (= q - p) does NOT depend on your choice of origin.

If this is what's going on with you, I have to say that I think they spend too much time/emphasis on this at a time when you're just getting used to the concepts. And so to a large extent I'd say don't worry too much about it - you should be able to pick a lot of it up "by osmosis", and in further lectures you'll probably find you don't need to worry that much (in that you will always be dealing with the form v = (x, y, z) where all you really care about are the values of x, y, and z).
I was just reading my c4 book actually and thought that the PQ notation was dodgy
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#18
(Original post by DFranklin)
What's the book?

As I understand it, you're just starting a maths degree. In my experience, one thing books/lecturers tend to go on about a fair bit (if you're being introduced to vectors at university level) is how/whether what you're doing depends on your choice of coordinates.

In particular, if you have points P, Q, and you define vectors p, q to be OP, OQ, respectively, then your vectors depend on where you've decided to put the origin. But the vector PQ (= q - p) does NOT depend on your choice of origin.

If this is what's going on with you, I have to say that I think they spend too much time/emphasis on this at a time when you're just getting used to the concepts. And so to a large extent I'd say don't worry too much about it - you should be able to pick a lot of it up "by osmosis", and in further lectures you'll probably find you don't need to worry that much (in that you will always be dealing with the form v = (x, y, z) where all you really care about are the values of x, y, and z).
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