# 3psi for a circle using the metric system

• Apr 7th 2011, 12:35 AM
Robd83
3psi for a circle using the metric system
Hello,
Im trying to figure out a metric formula for Pi(r)²(3psi) without having to do any conversions. I will be using mm instead of in, and kg instead of lbs. Is this possible?

Everything I have tried does not equal the same amount as when I do the whole problem in non-metric, then convert the lbs result to kg. I looked at other places online, but that started getting me into kPa which I have no idea about.

Thanks in advance for you help!
• Apr 7th 2011, 01:04 AM
earboth
Quote:

Originally Posted by Robd83
Hello,
Im trying to figure out a metric formula for Pi(r)²(3psi) without having to do any conversions. I will be using mm instead of in, and kg instead of lbs. Is this possible?

Everything I have tried does not equal the same amount as when I do the whole problem in non-metric, then convert the lbs result to kg. I looked at other places online, but that started getting me into kPa which I have no idea about.

Thanks in advance for you help!

1. I assume that you want to calculate the value of a force, right?

2. Forces are measured in N (Newton). kg is the unit for a mass. The weight (force!) of a mass of 1 kg is nearly 9.81 N (on Earth).

3. A force of 1 lb correspond to a force of 4.448222 N

4. the area of $1\ square-inch = (25.4\ mm)^2 = 645.16\ mm^2$

$\pi \cdot r^2 \cdot 3\ psi = \pi \cdot r^2 \cdot 3 \ lb \cdot \dfrac{4.448222\ \frac N{lb}}{645.16\ mm^2}$