Units_in_MC.xmcd
9/25/2007
Using Units (SI)
Units of Pressure - Pascal (Pa), Pounds per square inch (psi) which is really
lb-force per square inch
1
lbf
2
3
= 6.895 × 10 Pa
6895Pa = 1 ⋅ psi
in
1
lbf
2
3
= 1 ⋅ psi
1psi = 6.895 × 10 Pa
in
Now, multiplying psi * in^2 yields a force:
2
1psi⋅ 1 in = 4.448 N
Remember, there is a difference between lb (pound-mass) and
lbf (pound force)
So:
4.448N = 1 ⋅ lbf
(substitute lbf for units)
if you use lb, then you get strange results such as:
4.448N = 9.806
m
2
⋅ lb
s
You might recognize the 9.806 m/sec^2 as the acceleration of gravity.
Unfortunately, if this was used in a complex function, you would have no
idea why you had strange values and units. The lb is pound-mass as far
as Mathcad is concerned.
Units_in_MC.xmcd
9/25/2007
To set the units for an entire system, use Tools - Worksheet Options