Piston Stop at TDC?
04-23-2010, 03:28 PM
#272
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another way to look at Velocity and motion.
Velocity is motion with a direction or the rate at which something changes it's position relative to a point...it is the direction which differentiates velocity from speed. They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged.
Piston example....simplified..but it shows the concept.
Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second.
What was/is it's velocity with respect to TDC...simple it's zero...the vector down is countered by the vector up...with respect to TDC is has traveled 0 inches in one second.
What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter.
The piston has a Velocity and Instantaneous Velocity of Zero but is still has a speed of 6 inches/second...as long as the crank is turning.
Another proof. You can span an interval at any location along the pistons velocity/position curve...no matter how small you make that interval or where you locate it...you can even have it include TDC and you will always come up with motion.
There is no interval on that velocity curve for which a stop can be shown.
04-23-2010, 10:36 PM
#273
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Join Date: Jan 2006
Location: Puerto Rico
Posts: 3,926
I guess it is convenient for you to continue to ignore the fact that the graph you mentioned as not reaching TDC, was a kinematically calculated graph.
I guess it is convenient for you to continue to ignore the fact that you keep on passing misinformation regarding basic concepts in physics and mechanics.
Case in point?.... my friend, you are a fountain for those. Example?
And?
another way to look at Velocity and motion.
Velocity is motion with a direction or the rate at which something changes it's position relative to a point...it is the direction which differentiates velocity from speed. They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged.
Piston example....simplified..but it shows the concept.
Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second.
What was/is it's velocity with respect to TDC...simple it's zero...the vector down is countered by the vector up...with respect to TDC is has traveled 0 inches in one second.
What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter.
The piston has a Velocity and Instantaneous Velocity of Zero but is still has a speed of 6 inches/second...as long as the crank is turning.
Another proof. You can span an interval at any location along the pistons velocity/position curve...no matter how small you make that interval or where you locate it...you can even have it include TDC and you will always come up with motion.
There is no interval on that velocity curve for which a stop can be shown.
Velocity is motion with a direction or the rate at which something changes it's position relative to a point...it is the direction which differentiates velocity from speed. They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged.
Piston example....simplified..but it shows the concept.
Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second.
What was/is it's velocity with respect to TDC...simple it's zero...the vector down is countered by the vector up...with respect to TDC is has traveled 0 inches in one second.
What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter.
The piston has a Velocity and Instantaneous Velocity of Zero but is still has a speed of 6 inches/second...as long as the crank is turning.
Another proof. You can span an interval at any location along the pistons velocity/position curve...no matter how small you make that interval or where you locate it...you can even have it include TDC and you will always come up with motion.
There is no interval on that velocity curve for which a stop can be shown.
.... you go and repeat the same explanation for something it has been explained ad nauseam, state that "They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged."...... to do exactly just that? Or didn't you just calculated a value for speed to address velocity at the end?Let me see.... for that calculated speed of 6"/s, you shut the engine down after one revolution..... will that make the speed of the piston 3"/s calculated 1 second after it's shut down? .... or 2"/s 2 seconds after it's shut down? Or better yet, does a bus that stops after traveling 60 miles in one hour, have a speed of 60 MPH when it stops? OR..... what happened when it had to stop to pay a toll?.... it still made the 60 mile trip in one hour, yet it did stop + it also had to increase its speed in order to make up for time. IOW.... it's a concept not applicable to the case under scrutiny. OR ......does the piston change direction with a speed of 6"/s?.... as you now infer with that statement?
You continue to use the law of averages as the one and only tool for everything, and continue to use contradictory concepts by doing just that.... incorrectly interchanging them. What do I mean? Quoting you again....
"Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second. What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter."
So.... is it under a constant acceleration of 12"/s^2? ....and what was the speed at t = 3 seconds? Or is the "model" under a constant speed which is also the same speed it "starts" at and acceleration = 0? if so..... how did it accelerate there? ... if the piston in reality returns to TDC, how can it maintain the same speed across its stroke and change direction + (again) maintain the same speed?
You continue to use the sum of items averaged (6"/s) to justify the non-existence of a stop, yet neglect to recognize the individual components of that sum? How is the sum or average possible then? To top everything, you apply the result of that average (6"/s) to every component of that sum + use a concept (speed) that perfectly allows for stops to occur..... or didn't you know that velocity (as in speed with direction) is not constant for a piston through its stroke distance? .... albeit the fact that the angular velocity (angular speed CW) of the CKP may be? Oh!..... but the piston goes through a strokex2 during the same constant time...... yes, but the question is specific to one of the components of that average..... isn't it?
You continue to be stuck with 100% one dimensional linear models to try to explain or attempt to prove something that is totally different..... simple harmonic motion.... and that is a
... get it?
04-24-2010, 12:30 AM
#274
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Join Date: May 2006
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Posts: 744
I guess it is convenient for you to continue to ignore the fact that it was measured, corrected for in the degree wheel position, and then used.
I guess it is convenient for you to continue to ignore the fact that the graph you mentioned as not reaching TDC, was a kinematically calculated graph.
I guess it is convenient for you to continue to ignore the fact that you keep on passing misinformation regarding basic concepts in physics and mechanics.
Case in point?.... my friend, you are a fountain for those. Example?
And?
.... you go and repeat the same explanation for something it has been explained ad nauseam, state that "They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged."...... to do exactly just that? Or didn't you just calculated a value for speed to address velocity at the end?
Let me see.... for that calculated speed of 6"/s, you shut the engine down after one revolution..... will that make the speed of the piston 3"/s calculated 1 second after it's shut down? .... or 2"/s 2 seconds after it's shut down? Or better yet, does a bus that stops after traveling 60 miles in one hour, have a speed of 60 MPH when it stops? OR..... what happened when it had to stop to pay a toll?.... it still made the 60 mile trip in one hour, yet it did stop + it also had to increase its speed in order to make up for time. IOW.... it's a concept not applicable to the case under scrutiny. OR ......does the piston change direction with a speed of 6"/s?.... as you now infer with that statement?
You continue to use the law of averages as the one and only tool for everything, and continue to use contradictory concepts by doing just that.... incorrectly interchanging them. What do I mean? Quoting you again....
"Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second. What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter."
So.... is it under a constant acceleration of 12"/s^2? ....and what was the speed at t = 3 seconds? Or is the "model" under a constant speed which is also the same speed it "starts" at and acceleration = 0? if so..... how did it accelerate there? ... if the piston in reality returns to TDC, how can it maintain the same speed across its stroke and change direction + (again) maintain the same speed?
You continue to use the sum of items averaged (6"/s) to justify the non-existence of a stop, yet neglect to recognize the individual components of that sum? How is the sum or average possible then? To top everything, you apply the result of that average (6"/s) to every component of that sum + use a concept (speed) that perfectly allows for stops to occur..... or didn't you know that velocity (as in speed with direction) is not constant for a piston through its stroke distance? .... albeit the fact that the angular velocity (angular speed CW) of the CKP may be? Oh!..... but the piston goes through a strokex2 during the same constant time...... yes, but the question is specific to one of the components of that average..... isn't it?
You continue to be stuck with 100% one dimensional linear models to try to explain or attempt to prove something that is totally different..... simple harmonic motion.... and that is a... get it?
I guess it is convenient for you to continue to ignore the fact that the graph you mentioned as not reaching TDC, was a kinematically calculated graph.
I guess it is convenient for you to continue to ignore the fact that you keep on passing misinformation regarding basic concepts in physics and mechanics.
Case in point?.... my friend, you are a fountain for those. Example?
And?
.... you go and repeat the same explanation for something it has been explained ad nauseam, state that "They both use the same units of measure ie..m/s..mph..etc...and are usually incorrectly interchanged."...... to do exactly just that? Or didn't you just calculated a value for speed to address velocity at the end?Let me see.... for that calculated speed of 6"/s, you shut the engine down after one revolution..... will that make the speed of the piston 3"/s calculated 1 second after it's shut down? .... or 2"/s 2 seconds after it's shut down? Or better yet, does a bus that stops after traveling 60 miles in one hour, have a speed of 60 MPH when it stops? OR..... what happened when it had to stop to pay a toll?.... it still made the 60 mile trip in one hour, yet it did stop + it also had to increase its speed in order to make up for time. IOW.... it's a concept not applicable to the case under scrutiny. OR ......does the piston change direction with a speed of 6"/s?.... as you now infer with that statement?
You continue to use the law of averages as the one and only tool for everything, and continue to use contradictory concepts by doing just that.... incorrectly interchanging them. What do I mean? Quoting you again....
"Piston starts at TDC moves down 3 inches to BDC and then back up 3 inches to TDC...it does this all in 1 second. What was/is it's speed...3 inches + 3inches /1 second = 6 inches/second since speed is not directional the vectors do no counter."
So.... is it under a constant acceleration of 12"/s^2? ....and what was the speed at t = 3 seconds? Or is the "model" under a constant speed which is also the same speed it "starts" at and acceleration = 0? if so..... how did it accelerate there? ... if the piston in reality returns to TDC, how can it maintain the same speed across its stroke and change direction + (again) maintain the same speed?
You continue to use the sum of items averaged (6"/s) to justify the non-existence of a stop, yet neglect to recognize the individual components of that sum? How is the sum or average possible then? To top everything, you apply the result of that average (6"/s) to every component of that sum + use a concept (speed) that perfectly allows for stops to occur..... or didn't you know that velocity (as in speed with direction) is not constant for a piston through its stroke distance? .... albeit the fact that the angular velocity (angular speed CW) of the CKP may be? Oh!..... but the piston goes through a strokex2 during the same constant time...... yes, but the question is specific to one of the components of that average..... isn't it?
You continue to be stuck with 100% one dimensional linear models to try to explain or attempt to prove something that is totally different..... simple harmonic motion.... and that is a
... get it?The entire interval was chosen to keep the explanation simple to follow as some people appreciate that...I could have just as easily chose an interval of 0.00005 degrees BTDC and 0.00005 degrees ATDC and arrived at a different value....the key here is...there would still be a non-zero value for the motion.
If you shut the engine down...you would have to say the speed "was" rather than the speed "is"...unless of course you fire the engine back up and decide to include the non running stage in your overall calculations...that could be done but that wouldn't make any sense.
...the classic example used has been described in every Physics textbook regarding speed and velocity....Some words were substituted to keep it on topic...the relationship is clear.
If you are unsatisfied with the average of 6inches/second for all points, then, as mentioned, pick a different interval...what you are looking for is an interval where all points in that interval have an instantaneous velocity of zero....like a pen at rest on a desk...or piston at TDC while the engine is turned off and static.
04-24-2010, 05:37 PM
#276
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Join Date: May 2006
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Posts: 744
Sorry..It looks like I missed this in the original post...
I can only use the numbers that you posted...If you have an alternate set, then post them up....perhaps the calculations\corrections have introduced more error...
calculations and manipulations on original data are never more accurate than that original data...for the most part that is....ie large spikes that are outside the normal range expected can sometimes be ignored and removed to make the original data more precise...vinyl record crackle being removed from a recording may be one example of this.
Your kinematically calculated graph should show a perfect rounding at the top...not a flat spot....your graph also indicates that the rod goes perpendicular and reach it's maximum extension at the same time the flattening occurs in that 359 degree range...which is not true....so you know there is error present.
Real case...
In a manufacturing plant where my company used to contract too, they have reciprocating pumps which move in the same manner as that of an ICE. They have a crank, rods, pistons etc...and the curves derived from their motion are the similar.
To not take the pumps apart and, thus, totally offline, and to confirm what vibration analysis picks up, a long rod connected to an electrical resistor is inserted through the head to make contact with the piston. The assembly is then bolted securely to the head. The pump is then rotated precisely via an electric motor. The changes in resistance of the metal rod moving up and down are then sent to a computer and plotter...years ago it was sent to a machine that would reproduce the motion on the other end via a stylus and paper.
The cycle is repeated multiple times to get a number of graphs to compare.
The curves are then centered and plotted close together one below the other. This allows the instrument techs to eyeball any anomalies that may be present. If a problem shows up on multiple passes then the problem is real.
Those graphs are normally perfectly curved without any flat areas present at the top....if there is a flattening or a "jump" then there is a problem.
A flat spot at the top of the curve indicates that the rod. wrist pin bore and/or the wrist pin bearings have worn beyond the tolerance of the lubricating fluid's ability to be able to make up for the lost volume of material.
A flat spot also indicates a failure is not far away as "jack Hammering" is taking place at those locations at each revolution.
Those kinetically derived graphs are precise enough to not degrade when blown up on D and E sized plots.
I go to great lengths to make sure I keep within all limitations. I provide examples that can be reproduced and I keep the language to that in which the majority of people can understand if they so choose.
I wouldn't be in the career position that I am in today if I did not understand the basics of physics and mechanics...you are wrong with that statement.
calculations and manipulations on original data are never more accurate than that original data...for the most part that is....ie large spikes that are outside the normal range expected can sometimes be ignored and removed to make the original data more precise...vinyl record crackle being removed from a recording may be one example of this.
Real case...
In a manufacturing plant where my company used to contract too, they have reciprocating pumps which move in the same manner as that of an ICE. They have a crank, rods, pistons etc...and the curves derived from their motion are the similar.
To not take the pumps apart and, thus, totally offline, and to confirm what vibration analysis picks up, a long rod connected to an electrical resistor is inserted through the head to make contact with the piston. The assembly is then bolted securely to the head. The pump is then rotated precisely via an electric motor. The changes in resistance of the metal rod moving up and down are then sent to a computer and plotter...years ago it was sent to a machine that would reproduce the motion on the other end via a stylus and paper.
The cycle is repeated multiple times to get a number of graphs to compare.
The curves are then centered and plotted close together one below the other. This allows the instrument techs to eyeball any anomalies that may be present. If a problem shows up on multiple passes then the problem is real.
Those graphs are normally perfectly curved without any flat areas present at the top....if there is a flattening or a "jump" then there is a problem.
A flat spot at the top of the curve indicates that the rod. wrist pin bore and/or the wrist pin bearings have worn beyond the tolerance of the lubricating fluid's ability to be able to make up for the lost volume of material.
A flat spot also indicates a failure is not far away as "jack Hammering" is taking place at those locations at each revolution.
Those kinetically derived graphs are precise enough to not degrade when blown up on D and E sized plots.
I wouldn't be in the career position that I am in today if I did not understand the basics of physics and mechanics...you are wrong with that statement.
Last edited by Li0nHart; 04-24-2010 at 05:50 PM.
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