- #1

SpaceLight

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I need to find velocity when force, distance, and mass are known.

I found this equation: Fd = (M/2)V^2

The process to solve it is put forth by using the metric system. It would be a great help to know if (and how) I can use the imperial system only with this equation.

I'd like to take you through the process put forth, to hopefully reveal to you where I'm faltering.

-----------------------------------

"Step ONE: Weigh the object to find Mass. All other resistance, such as bearing resistance, being negligible, is not accounted for here; and so the WORK done on the object equals its KINETIC ENERGY. If grams, convert to Kg by dividing by 1,000. If pounds, convert to Kg by multiplying by .45"

> I have a disc that weighs .8 oz, which converts to .02268 Kg

-----------------------------------

"Step TWO: Set equations for WORK and KINETIC ENERGY so they are equal.

WORK = FORCE x DISTANCE; KINETIC ENERGY = 1/2 the MASS of the object x its VELOCITY squared.

That is: F x D = (M/2) X V^2.

Enter measurements for FORCE, DISTANCE and MASS.

Example: FORCE = 2 Newtons, DISTANCE = 5 meters, MASS = 0.7kg.

Therefore: (2 N) x (5 m) = (0.7kg/2) x v^2 "

> I converted oz to kg above for "M".

> Next, I have .3 lbs of force being applied to the disc. (The disc, by the way, is a motor rotor and the force applied is the repelling force via interaction between the rotor magnet and the stator's electromagnet...) So I need to convert .3 lbs to Newtons. 1 lbf = 4.448 N, so .3 lbs = 1.3344 Newtons.

> Next, for distance I'm assuming it's the circumference of the disc. A 2.365" diameter disc x Pi = 7.428465" circumference. Seems logical now to convert inches to metric, to keep with the metric equation. 1" = .0254m, so 7.428465" x .0254m = .188683011 m

My numbers so far: (1.3344 N) x (.188683011 m) = (.02268 kg/2) x v^2

More confusion sets in, whereby this equation is for figuring velocity linearly, not radially (as I need it to be). Therefore, at the end I attach the resolve for converting m/s to RPM, which involves finding the circumference, which I just did in step TWO, and is why I'm not sure about this equation altogether. But I keep on with it...

-----------------------------------

"Step THREE: Multiply and divide to simplify the equation.

Example: (2 N)*(5 m) = (0.7 kg/2)*v^2

becomes 10 N*m = (0.35 kg)*v^2."

My numbers: (1.3344 N) x (.188683011 m) = (.02268 kg/2) x v^2

becomes .251779 N*m = (.01134 kg) x v^2

-----------------------------------

"Step FOUR: Divide the left side of the equation by the number on the right side of the equation to isolate v^2.

Example: 10 N*m = (0.35 kg)*v^2

becomes 28.6 N*m/kg = v^2."

My numbers: .251779 N*m = (.01134 kg) x v^2

becomes 22.2027.. N*m/kg = v^2

-----------------------------------

"Step FIVE: Take the square root of the number on the left side of the equation to find the velocity.

Example: 28.6 N*m/kg = v^2

The square root of 28.6 equals 5.3, so the velocity is 5.3 m/s."

My numbers: 22.2027.. N*m/kg = v^2

Square root of 22.20273.. = 4.71197.. m/s

-----------------------------------

Now, for converting meters per second to RPM: RPM = V/(Pi*D).

RPM = 4.71197.. / 7.428465"

RPM = .634313..

?

Quite exhausting.

Any help on the matter, I am truly grateful.

I found this equation: Fd = (M/2)V^2

The process to solve it is put forth by using the metric system. It would be a great help to know if (and how) I can use the imperial system only with this equation.

I'd like to take you through the process put forth, to hopefully reveal to you where I'm faltering.

-----------------------------------

"Step ONE: Weigh the object to find Mass. All other resistance, such as bearing resistance, being negligible, is not accounted for here; and so the WORK done on the object equals its KINETIC ENERGY. If grams, convert to Kg by dividing by 1,000. If pounds, convert to Kg by multiplying by .45"

> I have a disc that weighs .8 oz, which converts to .02268 Kg

-----------------------------------

"Step TWO: Set equations for WORK and KINETIC ENERGY so they are equal.

WORK = FORCE x DISTANCE; KINETIC ENERGY = 1/2 the MASS of the object x its VELOCITY squared.

That is: F x D = (M/2) X V^2.

Enter measurements for FORCE, DISTANCE and MASS.

Example: FORCE = 2 Newtons, DISTANCE = 5 meters, MASS = 0.7kg.

Therefore: (2 N) x (5 m) = (0.7kg/2) x v^2 "

> I converted oz to kg above for "M".

> Next, I have .3 lbs of force being applied to the disc. (The disc, by the way, is a motor rotor and the force applied is the repelling force via interaction between the rotor magnet and the stator's electromagnet...) So I need to convert .3 lbs to Newtons. 1 lbf = 4.448 N, so .3 lbs = 1.3344 Newtons.

> Next, for distance I'm assuming it's the circumference of the disc. A 2.365" diameter disc x Pi = 7.428465" circumference. Seems logical now to convert inches to metric, to keep with the metric equation. 1" = .0254m, so 7.428465" x .0254m = .188683011 m

My numbers so far: (1.3344 N) x (.188683011 m) = (.02268 kg/2) x v^2

More confusion sets in, whereby this equation is for figuring velocity linearly, not radially (as I need it to be). Therefore, at the end I attach the resolve for converting m/s to RPM, which involves finding the circumference, which I just did in step TWO, and is why I'm not sure about this equation altogether. But I keep on with it...

-----------------------------------

"Step THREE: Multiply and divide to simplify the equation.

Example: (2 N)*(5 m) = (0.7 kg/2)*v^2

becomes 10 N*m = (0.35 kg)*v^2."

My numbers: (1.3344 N) x (.188683011 m) = (.02268 kg/2) x v^2

becomes .251779 N*m = (.01134 kg) x v^2

-----------------------------------

"Step FOUR: Divide the left side of the equation by the number on the right side of the equation to isolate v^2.

Example: 10 N*m = (0.35 kg)*v^2

becomes 28.6 N*m/kg = v^2."

My numbers: .251779 N*m = (.01134 kg) x v^2

becomes 22.2027.. N*m/kg = v^2

-----------------------------------

"Step FIVE: Take the square root of the number on the left side of the equation to find the velocity.

Example: 28.6 N*m/kg = v^2

The square root of 28.6 equals 5.3, so the velocity is 5.3 m/s."

My numbers: 22.2027.. N*m/kg = v^2

Square root of 22.20273.. = 4.71197.. m/s

-----------------------------------

Now, for converting meters per second to RPM: RPM = V/(Pi*D).

RPM = 4.71197.. / 7.428465"

RPM = .634313..

?

Quite exhausting.

Any help on the matter, I am truly grateful.

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