# Measuring Mass

1. Nov 10, 2006

### Swapnil

I was wondering, how is it that scientists measure inertial mass. I presume they use F=ma, and thus the mass of an object would be measured by applying a force on an object and finding out the resulting acceleration. Getting acceleration is simple, but how can they measure the force? Then if they can't measure the force, then how can they measure the mass?

2. Nov 10, 2006

### Staff: Mentor

Normally one measures the mass of an object by comparing it with a known standard mass, either directly using a balance, or indirectly by using a device (like a spring) that is calibrated using known masses.

One finds the mass of the "known" mass by comparing it with yet another standard mass, etc. The end of the chain is a chunk of platinum-iridium alloy stored under controlled conditions in a basement in Paris, whose mass is by definition exactly one kilogram.

3. Nov 11, 2006

### Swapnil

But doesn't a balance or a spring use the concept of forces to give you the measured mass? And forces are actually dependent on mass... I don't know why, but doesn't all of this seem to be circular?

4. Nov 11, 2006

### Staff: Mentor

The only requirement is that two objects with the same mass be affected equally by equal forces.

5. Nov 12, 2006

### destinct

mass is a si measurement therefore you can think of it as the beggining...like jtbell said it is defined in paris by a piece of metal which is defined to be 1Kg