In this exploration, acceleration was assumed to be constant. Consider the case where the acceleration is changing with time. This is known as "jerk." Jerk is often used in engineering, especially when constructing roller coasters. Humans can be safely subjected not only to a maximum acceleration, but also to a maximum jerk. Which of Shakina's statements regarding jerk is not correct?
"If the acceleration is decreasing over time, the jerk is negative."
"Jerk is the area under the acceleration vs. time graph."
"The units of jerk are m/s3."

- blackstreet23

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- blackstreet23

In this exploration, acceleration was assumed to be constant. Consider the case where the acceleration is changing with time. This is known as "jerk." Jerk is often used in engineering, especially when constructing roller coasters. Humans can be safely subjected not only to a maximum acceleration, but also to a maximum jerk. Which of Shakina's statements regarding jerk is not correct?
1- "If the acceleration is decreasing over time, the jerk is negative."
2- "Jerk is the area under the acceleration vs. time graph."
3- "The units of jerk are m/s3."
4- "Jerk is the slope of the acceleration vs. time graph."

- blackstreet23

@PlasmaFuzer
@Shalante
@freckles

- anonymous

Ok so I take it you are able to select multiple answers that are correct yes?

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## More answers

- anonymous

Oh darn nm you are supposed to select the INCORRECT statements.... ok then no problem

- anonymous

So let me ask you a question... If velocity changes with respect to time does this mean there is an acceleration?

- anonymous

Assuming of course the mass of the object isn't changing that is :D

- blackstreet23

yes

- anonymous

ok then what are the units of velocity and what are the units of acceleration.... and how are the two related?

- blackstreet23

units of velocity are m/s and of acceleration m/s^2

- anonymous

Correct... how are the two related to one another?

- blackstreet23

they are related because the derivative of one of them gives us the other one

- blackstreet23

right?

- anonymous

Exactley the derivative of the velocity function gives us the acceleration function.... tell me what does it mean to find the derivative of a curve at a point?

- anonymous

And before you start sweating this is actually a lot easier to imagine and explain than the integral before :D

- blackstreet23

umm. the derivative of a curve point?

- anonymous

Yes.... so we said that:
\[a=\frac{ dv }{ dt }\]
But to be more precise it is really:
\[ a(t)=\frac{ d }{ dt } v(t) \]
For an object who has a constant mass....
Therefore at the point t=T what is the meaning of :
\[ a(T)=\frac{ d }{ dt } v(T) \]

- anonymous

Geometrically, what is its meaning... Just like the integral is the area under the curve... what does this derivative at the point T mean?

- anonymous

If you dont know you can just say btw

- anonymous

No judgements here :D we all have to learn it at some point I don't hold it against people for not knowing

- anonymous

Or getting it wrong or making a mistake for that matter

- blackstreet23

the derivative is the slope of the tangent

- anonymous

Bingo nailed it.... So you should have all the pieces to get this one... Please go through the choices for me and explain to me why one first or why one doesnt please? :D

- anonymous

fits*

- blackstreet23

if the acceleration is decreasing, the jerk is negative? is that so?

- anonymous

I dont know is it? Please try and reason it out.... Start with this... We already agreed on the relationship between velocity and acceleration... If the velocity is decreasing what can you say about acceleration?

- blackstreet23

ohh I think i got it. Since the derivative means the change of something over time. That means that the jerk has to be the change of acceleration over time. Right?

- anonymous

Exactley :D :D

- blackstreet23

if the velocity is decreasing is accelaration has a different sign

- anonymous

Different?

- blackstreet23

like if the velocity is negative and acceleration positive, it starts backwards, slow down and then goes to the front and vice-versa

- blackstreet23

ohh so the same principle applies to acceleration?

- anonymous

Exactley correct, but note the use of the word DECREASING.... if the velocity is negative and is DECREASING it is getting more negative no?

- anonymous

And in this case the acceleration is also negative so it happens to be the SAME sign as that of velocity

- blackstreet23

i guess

- anonymous

Your situation is when velocity is negative and begins to INCREASE.... then it has a positive acceleration

- blackstreet23

but if the acceleration is positive and the jerk negative, the acceleration decreases?

- anonymous

Exactley :D:D

- anonymous

but also if the acceleration is NEGATIVE and DECREASING the jerk is also negative
Does this make sense?

- blackstreet23

and if the acceleration is negative and the jerk is negative as well it becomes more negative, just as the same as (velocity and acceleration)

- anonymous

change in acceleration over time is what is important not the absolute sign

- blackstreet23

yes it does!

- blackstreet23

i mean yes it does make sense!

- anonymous

Oh yes sorry didnt see that post... yes that is correct

- blackstreet23

I get it now :D

- anonymous

Ok so is option 1 true or false?

- blackstreet23

true

- blackstreet23

1-T

- anonymous

bingo.... next

- anonymous

because we are of course looking for what is INCORRECT

- blackstreet23

2 is the false one right?

- anonymous

Correct yes that is the answer

- blackstreet23

jerk is the derivative of the graph (acceleration vs time) and not the integral of it (area under the curve)

- anonymous

What would that represent?

- blackstreet23

that would be velocity

- anonymous

Exactley on both posts :D :D

- anonymous

So I take it you got it but just to be thorough do the units make sense of jerk?

- blackstreet23

You are a physics genius lol. I am going to look for you in any question i ask haha

- anonymous

Hahahaha why thank you, but unfortunately I am in school myself so I only come here when I have some spare time to help out :(

- blackstreet23

ohh no why the units are m/s^3?

- anonymous

But I do check my emails so if I have a moment and I see your post I will try to help, but sometimes I wont have the same amount of free time so keep that in mind

- anonymous

Ahh well let me ask you a question... why are the units of acceleration m/s^2 ?

- blackstreet23

\[\frac{ m }{ s } * \frac{ 1 }{ s }\]

- blackstreet23

velocity / time

- blackstreet23

so it would be (acceleration / time)

- anonymous

so you really mean:
\[\frac{ \frac{m}{s}}{s} \]
... Yes exactley

- anonymous

Yes exactley....

- anonymous

\[\frac{ \frac{m}{s^2}}{s}\]

- blackstreet23

ohh ok. Thanks a lot! Btw can i ask what is your major and if you are getting your Associates, Bachelors or Masters? lol

- anonymous

Im actually in a Ph.D program for plasma physics

- blackstreet23

sorry just got curious

- anonymous

Its alright :D

- blackstreet23

ohhh ok. I am talking to a Doctor! that is so cool!!!

- anonymous

hahaha not yet no but maybe in a few years

- blackstreet23

But what is plasma physics about?

- anonymous

Well I have always been interested in fusion energy... So I decided to pursue it and study man made plasmas specifically tokamak plasmas

- anonymous

Its hard to give a simple explanation, but if you think it is interesting I invite you to check out wikipedia.... It is an invaluable resource to get a once over viewpoint of a topic, though I should not you always need to go deeper if you are asked to actually write a paper or do research since it is only really a summary of things.

- anonymous

This should be a good place to start: http://fusionforenergy.europa.eu/understandingfusion/

- anonymous

And this one also: https://en.wikipedia.org/wiki/Tokamak if you want to get a little more

- anonymous

But I would suggest saving it till you have a little free time.... make sure to finish your hw first so you dont have it hanging over your head... that is a terrible feeling

- blackstreet23

haha yeah i know ...

- blackstreet23

and btw what motivated you to go for your masters?

- blackstreet23

sorry P.h.D

- anonymous

Hmmm well that's a good question and it doesn't have a simple answer; but I guess it ultimately came down to the fact that I decided to pursue physics so I could help out in this field. If I were to stop at a bachelors level then I felt I couldn't really contribute the way I wanted to (or at least doing the things I liked to do). So yea, suffice it to say I always found this stuff interesting and it always drove me to want to know more.

- anonymous

A real turning point was when I stopped looking at hw problems and study problems as just a means to an end (a good grade) and started looking at them as valuable opportunities to practice my reasoning skills on a specific topic... If I couldn't do it then obviously I didn't understand it.

- anonymous

But at the end of the day I'm with Feynman on this one.... I just got interested in this stuff and decided to want to pursue it. I really feel anyone can do it, it just comes down to finding an interest and passion for it that can carry you through the dull bits in order to be able to enjoy the more satisfying bits (which also happen to be the more difficult bits).

- blackstreet23

ohh i loved your answer is pretty enlightening!

- blackstreet23

btw do you have to go. Because it would be helpful if you could explain to me how to do the previous problem. The one I told you to skip. Without the simulator haha

- anonymous

Sure no problem, but give me a min I have been going back and forth from the kitchen I'm making something to eat.

- blackstreet23

ohh no problem

- anonymous

are u here?

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