Rate of change of acceleration - basic

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Discussion Overview

The discussion revolves around the plotting of the rate of change of acceleration against time, specifically using "g" as the unit of acceleration. Participants explore the appropriate labeling of the y-axis and clarify the nature of the data being plotted.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether the y-axis should be labeled as "dg" or "dg/dt" depending on the nature of the data being plotted.
  • There is uncertainty about whether the acceleration being measured is in terms of "g" (the acceleration due to gravity) or if "g" is used as a general label for acceleration.
  • Participants discuss the implications of measuring changes in acceleration over fixed time intervals and how this affects the labeling of the graph.
  • One participant suggests that if acceleration is measured in "g", then the rate of change of acceleration should also be expressed in terms of "g".
  • There is a suggestion that "g" is a constant value, which raises questions about the validity of using "Δg" in the context of the discussion.
  • Some participants express confusion about the calculations being performed in Excel and how to represent the results graphically.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the appropriate labeling of the y-axis or the nature of the measurements being taken. Multiple competing views remain regarding the interpretation of "g" and how to accurately represent the data.

Contextual Notes

There are unresolved questions about the definitions of the variables being used, the assumptions underlying the measurements, and the specific calculations performed in the spreadsheet.

Micky
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I'm plotting rate of change of acceleration against time. Acceleration is measured as "g". Time is plotted on the x axis, rate of change of acceleration is plotted on the y axis. Is "dg" a valid label for the "y" axis?

Thanks
 
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I'm not clear as to what you are actually plotting. Are you plotting acceleration versus time in order to find the rate of change of the acceleration?

Or are you plotting the rate of change of acceleration versus time, as you state? If the later, you can call the y-axis [itex]\frac{da}{dt}[/itex] or [itex]\frac{dg}{dt}[/itex].

Or are you plotting change of g versus t?
 
Hi Doc

I already have rate of change of acceleration (in the vertical direction) measured as rate of change of "g" which I can plot against time, I can then show a certain rate of change of acceleration during a unit of time (in this case 0.01s)

I've assumed that rate of change of acceleration is the same as rate of change of "g", is this correct?

I'm uncertain if the "y" axis should be "dg" or "dg/dt"

Thanks
 
Originally posted by Micky
I already have rate of change of acceleration (in the vertical direction) measured as rate of change of "g" which I can plot against time, I can then show a certain rate of change of acceleration during a unit of time (in this case 0.01s)
Are you measuring your acceleration in terms of g the acceleration due to gravity? Or is it just coincidence that you use the letter "g" to refer to acceleration?

It sounds like you are actually measuring changes in g during fixed intervals (0.01 sec) at various times. Is this right? If so then whether you plot Δg or Δg/dt doesn't matter, since they will be proportional. But you better know which you are plotting, since that will determine your label.
I've assumed that rate of change of acceleration is the same as rate of change of "g", is this correct?
You tell me. If you are calling the acceleration "g" (why not call it "a"?) then the rate of change of g is the same as the rate of change of a.
I'm uncertain if the "y" axis should be "dg" or "dg/dt"
What you call the y-axis depends on what you are plotting: are you plotting Δg or Δg/(0.01) ?
 
Hi Doc
Are you measuring your acceleration in terms of g the acceleration due to gravity?
Acceleration measured in terms of gravity.
It sounds like you are actually measuring changes in g during fixed intervals (0.01 sec) at various times. Is this right?
Yes.
But you better know which you are plotting, since that will determine your label.
Absolutely.
If you are calling the acceleration "g" (why not call it "a"?) then the rate of change of g is the same as the rate of change of a.
I can certainly call it "a".
What you call the y-axis depends on what you are plotting: are you plotting ?g or ?g/(0.01) ?
Right, I think I see it know :wink: The Y axis is dg, but the graph is dg/t [?]

Thanks Doc

How do you post the delta triangle?
 
Ah... You are measuring acceleration "a" in units of "g". Do not call the y-axis "g" or "Δg", call it "a" or "Δa" or "Δa/Δt", depending on what you are measuring.

I still don't know what you are actually measuring. Here's my guess at what your data might look like:
T= 1 sec; Δa = .12 g (measured over a 0.01 sec interval)
T= 2 sec; Δa = .04 g (measured over a 0.01 sec interval)

Etc... Am I even close? What is it that you are measuring the Δa of? How are you making the measurements?

(Note that if you were to list the rate of change of a, it would be measured in units of g/sec not g.)

To find out to make the Δ, just quote this post and look.
 
I'm measuring the acceleration of a body in the vertical direction using an accelerometer and datalogger. The raw data is downloaded to a laptop and saved as a text file. The data is presented in two columns, time (measured in units of 0.01s) and acceleration (measured as g). So this means that at any given point in time I know the acceleration of the body.

I load the text file into Excel and calculate how acceleration changes from one measurement to the next, therefore these units must still be g, not Δg [?] ... confused again!

I can then plot a graph of the results of the calculation against time to show the Δg/t [?] [?]

M
 
Originally posted by Micky
...
I load the text file into Excel and calculate how acceleration changes from one measurement to the next, therefore these units must still be g, not Δg [?] ... confused again!
I think I see what you are doing now. Your spreadsheet calculates Δa at each time t (I'll bet that you say Δa(at t = n) = a(at t = n+1) - a(at t = n)... or something like that). Good.

Note that "g" is a constant (equals about 9.8 m/s2) so Δg makes no sense. You are going to graph Δa as a function of time. Also note that both a and Δa will have units of "g".
I can then plot a graph of the results of the calculation against time to show the Δg/t [?] [?]
Assuming your spreadsheet finds Δa, your graph would show Δa plotted against time. You will be able to see how the acceleration varies over time.
 
Thanks for that Doc :smile:
 

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