How to get the real object speed?

[Moon54]

I am trying to get the real object speed at a current moment. The movement is circular. I have all the timings.

This is the data, the speed is in milisecounds, and the numbers represent the revolutions:

1. -504ms
2. -720ms
3. -1044ms
4. -1332ms

I know the average speed of the object, at revolution number one it was 504ms / revolution, but i don't know what the real speed was (I need the begin one and ending one). It's just the average speed, and this site right here: https://m.wikihow.com/Calculate-Speed

Tells, that there is a way to do it, but i wasn't able to find how to do it. Anyone could help with it?

 

[phinds]

No, you do NOT have "speed in milliseconds ", you have revolutions/ms. Suppose the item is 1 meter in diameter, can you then calculate the speed? Suppose it is 100 meters in diameter, can you then calculate the speed? Will the two be the same?

 

[Moon54]

No, you do NOT have "speed in milliseconds ", you have revolutions/ms. Suppose the item is 1 meter in diameter, can you then calculate the speed? Suppose it is 100 meters in diameter, can you then calculate the speed? Will the two be the same?

I just need the formula to calculate it. Yes, i DO have the speed. Do i have to post it? I guess no, because all i need, is the formula, not a single fixed value, correct?

Ps. Let's assume it's 1 meter, or whatever you want, to make it easier in this example.

 

[berkeman]

I am trying to get the real object speed at a current moment.

Yes, i DO have the speed. Do i have to post it?

"Well, which is it young fella?" (Quiz Question -- what movie is that from?)

If you have the time per orbit/revolution, and you have the distance (do you know how to calculate the circumference of a circle, then you should have all that you need, no?

 

[Moon54]

"Well, which is it young fella?" (Quiz Question -- which movie is that from?)

If you have the time per orbit/revolution, and you have the distance (do you know how to calculate the circumference of a circle, then you should have all that you need, no?

No. I have the average speed per 1 reveolution. Not the beging - ending speed per revolution.

 

[berkeman]

No. I have the average speed per 1 reveolution. Not the beging - ending speed per revolution.

So you're saying since the time per revolution is a little different, you would like to fit an acceleration versus time to the datapoints, and infer the velocity versus time from that? The angular acceleration versus time does not look linear to me, but I can put your datapoints into Excel to look into it further. Can you say any more about the physical setup? That could help in the data analysis. Thanks.

 

[Moon54]

So you're saying since the time per revolution is a little different, you would like to fit an acceleration versus time to the datapoints, and infer the velocity versus time from that? The angular acceleration versus time does not look linear to me, but I can put your datapoints into Excel to look into it further. Can you say any more about the physical setup? That could help in the data analysis. Thanks.

There is no any simple formula to just calculate it? Helping in this particular case, means nothing, since it's 1 of many of them. Unless the solution is universal.

 

[berkeman]

There is no any simple formula to just calculate it? Helping in this particular case, means nothing, since it's 1 of many of them. Unless the solution is universal.

Of course there are fairly simple formulas for simple circular motion. For uniform circular motion, you will get the same period (time to go around) for each revolution. For uniform angular acceleration, you will get a shorter period for each revolution, and the equations for that are fairly straightforward. If the angular acceleration is not uniform, you will need to do some curve fitting to try to approximate what is going on.

Is there are reason you are being so obtuse in your replies? If the test setup is proprietary to your company, that is fine and we'll do the best we can. If this is data from your high school experiment, and you are having trouble understanding the data variation, we can help with that level too. The more information you can give us, the better we can help you.

I'm also trying to avoid doing an hour of simulations and curve fitting on a Sunday afternoon at home with my family if I don't have to. It all depends on where your question is coming from. Does that make sense?

 

[berkeman]

"Well, which is it young fella?" (Quiz Question -- what movie is that from?)

Just to lighten up the thread a bit...

Spoiler

Raising Arizona:

https://www.gunandgame.com/threads/funny-movie-quotes.58692/

: Gale: All right, you hayseeds, it's a stick-up. Everybody freeze. Everybody down on the ground.
Feisty Hayseed: Well, which is it, young feller? You want I should freeze or get down on the ground? Mean to say, if'n I freeze, I can't rightly drop. And if'n I drop, I'm a-gonna be in motion. You see...
Gale: Shut up!
Feisty Hayseed: Okay then.
Gale: Everybody down on the ground!
Evelle: Y'all can just forget that part about freezin' now.
Gale: Better still to get down there.
Evelle: Yeah, y'all hear that, don't ya?
[Everybody lays down. Gale looks at the now-empty teller windows]
Gale: crap! Where'd all the tellers go?
Teller's voices: We're down here, sir.
Evelle: They're on the floor as you commanded, Gale.

 

[Moon54]

Of course there are fairly simple formulas for simple circular motion. For uniform circular motion, you will get the same period (time to go around) for each revolution. For uniform angular acceleration, you will get a shorter period for each revolution, and the equations for that are fairly straightforward. If the angular acceleration is not uniform, you will need to do some curve fitting to try to approximate what is going on.

Is there are reason you are being so obtuse in your replies? If the test setup is proprietary to your company, that is fine and we'll do the best we can. If this is data from your high school experiment, and you are having trouble understanding the data variation, we can help with that level too. The more information you can give us, the better we can help you.

I'm also trying to avoid doing an hour of simulations and curve fitting on a Sunday afternoon at home with my family if I don't have to. It all depends on where your question is coming from. Does that make sense?

Again, it really doesn't help me in anything, if you just simulate / fit the data, and send the results. What i need is understand, WHAT kind of fitting is this? Exactly, the name of algorithm / formula.
It's not any school project, or company. I don't work in any company.

 

[Vanadium 50]

"Well, which is it young fella?" (Quiz Question -- what movie is that from?)

Does it involve Huggies?

if you just simulate / fit the data, and send the results. What i need is understand

You are asking for our help. If you were a little more informative (and a little less entitled and demanding) it would be easier to provide it. As it is, your question is incomplete. Why are you unwilling to complete it for us? And why are you unwilling to provide context?

 

[Moon54]

Does it involve Huggies?
You are asking for our help. If you were a little more informative (and a little less entitled and demanding) it would be easier to provide it. As it is, your question is incomplete. Why are you unwilling to complete it for us? And why are you unwilling to provide context?

What is incomplete? I asked clearly, how to get the beginning and ending revolution speed value. What is incomplete here? If i ask, i want the median formula, do i have to add i want it for 4, 5, 6, 7? Isn't the median tells you enough?

 

[berkeman]

What is incomplete? I asked clearly, how to get the beginning and ending revolution speed value. What is incomplete here? If i ask, i want the median formula, do i have to add i want it for 4, 5, 6, 7? Isn't the median tells you enough?

No, are the numbers in your first post relative or absolute times? What do your graphs look like so far?

​

 

[berkeman]

And are you familiar with these basic equations?

http://hyperphysics.phy-astr.gsu.edu/hbase/circ.html

 

[Moon54]

And are you familiar with these basic equations?

http://hyperphysics.phy-astr.gsu.edu/hbase/circ.html
View attachment 248024

1. I don't know, it doesn't matter for me.

2. No, i am not familiar with those, since i didn't have to use them ever.

3. I think i will just do it by my own way instead. I just create an algorithm in the software, and that's it. Faster, much more easier, and maybe as accurate.

Can you give me the name of curve fit method you wanted to use?

 

[berkeman]

Can you give me the name of curve fit method you wanted to use?

"Least squares" is a fairly simple fitting method. See this PF thread for other options:

https://www.physicsforums.com/threads/curve-fitting.931630/

 

[ZapperZ]

First of all, let me make this very clear: Your question and post are extremely confusing and ambiguous. You may think you have it very clear in your head, but you omitted a lot of that picture in your description, and worse still, you are using terminology in physics but in very erroneous and strange way.

I will show you exactly what I mean.

I am trying to get the real object speed at a current moment. The movement is circular. I have all the timings.

This is the data, the speed is in milisecounds, and the numbers represent the revolutions:

1. -504ms
2. -720ms
3. -1044ms
4. -1332ms

I know the average speed of the object, at revolution number one it was 504ms / revolution, but i don't know what the real speed was (I need the begin one and ending one). It's just the average speed, and this site right here: https://m.wikihow.com/Calculate-Speed

This is not "speed". What you wrote are "times", and more specifically, the PERIOD of revolution, which by definition, is the time taken for something to make one complete revolution or oscillation. "Speed" has the dimension of length/time, which is definitely something you do not have there. So when you insisted that you "know the average speed", this becomes a head-scratcher because those number that you wrote DO NOT represent speed.

Secondly, you keep emphasizing that you know the "speed of the object", but you need "real speed". This makes no sense unless you describe the type of motion. Is this a uniform circular motion? Is this something that spins and it is speeding up or slowing down (the latter may explain the negative signs you cited in your times?). Is this an extended object, i.e. an object that is spinning about some axis, rather than a mass that is moving in an orbit or circular motion? The "speed" of any part of an extended object depends not only on how fast it is spinning, but also on the distance from the axis of rotation, something you have not included. But then again, you may be asking about angular velocity, but that is still up in the air.

Do you see our confusion here? You may think you have included everything, but you really haven't. From our point of view, this is a very confusing mess, and your responses so far to some of the queries haven't clarified any.

Zz.

 

[berkeman]

3. I think i will just do it by my own way instead. I just create an algorithm in the software, and that's it. Faster, much more easier, and maybe as accurate.

So if I guess that your data is cumulative, and so I extract the new rotational period for each of the 4 revolutions, this is what the rotational speed looks like when I do a simple plot in Excel. It is increasing, but not uniformly, and not with a constant value of angular acceleration α. I don't know if this helps, but wherever you go next for help, you will need to present such data analysis (and hopefully a lot more information).

 

[Moon54]

First of all, let me make this very clear: Your question and post are extremely confusing and ambiguous. You may think you have it very clear in your head, but you omitted a lot of that picture in your description, and worse still, you are using terminology in physics but in very erroneous and strange way.

I will show you exactly what I mean.
This is not "speed". What you wrote are "times", and more specifically, the PERIOD of revolution, which by definition, is the time taken for something to make one complete revolution or oscillation. "Speed" has the dimension of length/time, which is definitely something you do not have there. So when you insisted that you "know the average speed", this becomes a head-scratcher because those number that you wrote DO NOT represent speed.

Secondly, you keep emphasizing that you know the "speed of the object", but you need "real speed". This makes no sense unless you describe the type of motion. Is this a uniform circular motion? Is this something that spins and it is speeding up or slowing down (the latter may explain the negative signs you cited in your times?). Is this an extended object, i.e. an object that is spinning about some axis, rather than a mass that is moving in an orbit or circular motion? The "speed" of any part of an extended object depends not only on how fast it is spinning, but also on the distance from the axis of rotation, something you have not included. But then again, you may be asking about angular velocity, but that is still up in the air.

Do you see our confusion here? You may think you have included everything, but you really haven't. From our point of view, this is a very confusing mess, and your responses so far to some of the queries haven't clarified any.

Zz.

All i know is this.
1. Deceleration is not constant, and it change every second, it also depends at what speed the object is
2. The speed always slows down
3. The mass is unknown
4. There is no any kind of axis, it's not a carousel, but more likely something that you place on the track, and spin. The origin doesn't matter also, since the object is on the track border.

5: Yes i DO have the average speed, once again. How it's not, if i can divide length / 504? I seid that it's a variable. You know what a variable is right? So you can put whatever you want there. 1meter, 67 centimeters or 11.6 km.

If having the choice, is the problem, then let's assume the length is 74 centimeters. I use centimeters / milliseconds.

504: 0.14682cm / ms
720: 0.102777cm / ms
1044: 0.0708cm / ms
1332: 0.0555555cm / ms

 

[sophiecentaur]

The OP started and seems to be continuing to use the wrong terminology for this and nothing can be sorted out until he/she starts to use the proper terms. Could it be to do with how the subject has been taught (with sloppy terminology) or that the OP has not used the information supplied on the course? Getting an understanding any part of Physics has to involve using the right (commonly agreed) terms and definitions; without that, it's impossible to have a meaningful conversation.

 

[ZapperZ]

All i know is this.
1. Deceleration is not constant, and it change every second, it also depends at what speed the object is

How would you know this, considering that all you can "see" is that it is slowing down. Slowing down does not mean the deceleration is changing.

2. The speed always slows down
3. The mass is unknown
4. There is no any kind of axis, it's not a carousel, but more likely something that you place on the track, and spin. The origin doesn't matter also, since the object is on the track border.

It does matter if we need to know the radius of path. Something that takes t seconds to make one complete revolution will have a different speed at a different radius than something that takes the same t seconds to make the same one revolution, but at a different radius. All you have is the time for it to make one revolution. All you can get out of that is the average angular velocity but not the linear speed.

5: Yes i DO have the average speed, once again. How it's not, if i can divide length / 504? I seid that it's a variable. You know what a variable is right? So you can put whatever you want there. 1meter, 67 centimeters or 11.6 km.

Read above. And pay attention to the data you have given. You gave a table of TIMES, not speed. So what you have is a set of times for one revolution (see the line in bold that I highlighted in my first post). That is a "period", not the average speed.

If having the choice, is the problem, then let's assume the length is 74 centimeters. I use centimeters / milliseconds.

If the length traveled is different for each of the times, then you need to also include the length! Otherwise, you've only given us partial information and expect us to understand what you did, which is absurd.

Hey, how about this novel idea: you present an accurate sketch of your setup.

My students often do not appreciate the importance of a proper sketch when they tackle a problem. They think that what they describe is very clear, at least in their heads. I'd like to show them your post so that they can see how vague and confusing things become without having a mental picture of the situation, while the originator thinks everything is crystal clear.

BTW, you still have not describe the nature of the path, i.e. is it a circle, an oval, a loop-de-loop, etc.. It is another example where your picture of your setup is not something that we have.

Zz.

 

[Moon54]

How would you know this, considering that all you can "see" is that it is slowing down. Slowing down does not mean the deceleration is changing.
It does matter if we need to know the radius of path. Something that takes t seconds to make one complete revolution will have a different speed at a different radius than something that takes the same t seconds to make the same one revolution, but at a different radius. All you have is the time for it to make one revolution. All you can get out of that is the average angular velocity but not the linear speed.
Read above. And pay attention to the data you have given. You gave a table of TIMES, not speed. So what you have is a set of times for one revolution (see the line in bold that I highlighted in my first post). That is a "period", not the average speed.
If the length traveled is different for each of the times, then you need to also include the length! Otherwise, you've only given us partial information and expect us to understand what you did, which is absurd.

Hey, how about this novel idea: you present an accurate sketch of your setup.

My students often do not appreciate the importance of a proper sketch when they tackle a problem. They think that what they describe is very clear, at least in their heads. I'd like to show them your post so that they can see how vague and confusing things become without having a mental picture of the situation, while the originator thinks everything is crystal clear.

BTW, you still have not describe the nature of the path, i.e. is it a circle, an oval, a loop-de-loop, etc.. It is another example where your picture of your setup is not something that we have.

Zz.

Listen. I don't have time to answer your 200 questions for my 1 i asked, understood? I added everything i know, if the data you got is not enough, then it means it can't be done. That's it. That you for help.

 

[berkeman]

I added everything i know, if the data you got is not enough, then it means it can't be done. That's it.

It certainly could be done. But based on how far we've gotten trying to help you with this problem, I think it's time to close the thread.

Thank you to everyone how has tried to help.