# Having trouble converting rpm to 1/s using unitConvert from symunit

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SamuLibero il 8 Mar 2023
Commentato: David Hill il 8 Mar 2023
Hi guys,
I'm using symunit for a project where I have to calculate the dimensions of an impeller. I'm using symunit to convert all the results accordingly to the book i'm refering to. But i'm having big problems working with it as soon as I try to convert rpm to 1/s.
u = symunit;
n = 2950 * u.rpm; % Given
w = vpa(unitConvert(n,(1/u.s))); % I need the angular velocity in 1/s for the next steps
For "w" I get 308.92 rad/s. Which if devided by rad (2*pi) would give the right result 49.01. But i don't understand why despide telling that I want the output in 1/s i get rad/s. Do I have to do the conversion manually every time or am I using unitConvert wrong?
Thank you for your help, I appreciate it! :)
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### Risposte (1)

David Hill il 8 Mar 2023
You want rps
u = symunit;
n = 2950 * u.rpm;
w = vpa(unitConvert(n,u.rps))
w =
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SamuLibero il 8 Mar 2023
Hi David,
thank you for repling. The problem I get with rps is that it doesn't simplify the measure unit correctly
next step would be to calculate the Torque:
P_imp = 5 * u.w % or kg * m^2 * s^-3
w = 5 * u.rps
M_imp = P_imp/w % I get kg * m^2 * s^-3 * rps^-1
if i then convert
M_imp = unitConvert(M_imp, u.N*u.m)
i get whereas i would need Nm
David Hill il 8 Mar 2023
Not sure, but multiplying by 2*pi*u.rad will take care of it. Maybe someone else has more insight. I don't like using symbolic units.
u = symunit;
n = 2950 * u.rpm;
w = vpa(unitConvert(n,u.rps));
P_imp = 5 * u.W
P_imp =
M_imp =

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