When someone asks us
about converting force to mass, Morehouse can now say we have an app for
that. Not only will our app convert force to mass, but it will convert
mass to force as well as convert units. It will convert force, torque, and
pressure units. Anyone interested in downloading the app can visit the
google play store https://play.google.com/store/apps/details?id=com.mhforce.localgravity or
scan the QR code below at the end of this article.

Let’s look at why this app is needed.

**Using Mass weights to calibrate
a force-measuring instrument can result in large measurement error**.

When metrologists talk
about measurement error, we’re talking about the difference between the nominal
value and what the instrument is reading. If 10,000 lbf is applied
to a force measuring device and the readout displays 10,002 lbf, then the
device has a 2 lbf bias. If we load the same force measuring device to 10,002 lbf,
we will have applied 10,000 lbf. This is a measurement error, and there
can be many different causes. After speaking with several professionals
inside the weighing industry, it has come to my attention that some labs use
mass weights to calibrate force devices. These include dynamometers, crane
scales, hand-held force gauges, and others. This can result in significant
measurement error.

Let’s quickly review the difference between mass and force. Mass, under almost every terrestrial circumstance, is the measure of matter in an object. Measuring force takes additional factors into account: air density, material density, and gravity. It’s the effect of gravity which can produce significant errors when comparing mass and force measurements.

It is very important
that the gravitational value for the Laboratory is established. The effect of
not doing this could be a variation in the force produced by the weight of
perhaps 0.1 % or more of reading. It is therefore strongly recommended
that you establish the local value of gravity (g) for your Laboratory and use
weights that have been calibrated at that gravitational constant.

Gravity is not constant
over the surface of the earth. The most extreme difference is 0.53 % between
the poles and the equator (983.2 cm/s2 at the former compared to 978.0 cm/s2 at
the latter). A force measuring device calibrated in one location using mass
weights then deployed somewhere else will produce different strains on the
physical element. The resulting measurement errors can be significant.

Correcting for the difference in force and mass measurements is possible. When a device is
adjusted for force measurements, the device will measure force without
additional error for gravity correction, air density correction and so on
needed.

The Morehouse app will
use your exact coordinates, go to NOAA’s website, and convert the mass value to
force using this formula.

Force = M x g /
9.80665 m/s2 *(note: to properly convert mass
to force material density and air density should be known) *This formula will have
additional errors that are likely less than 0.02 %. For more information on
mass to force please read https://www.mhforce.com/BlogPost/PostDetails/180?title=Force-Applications-for-Mass-Reference-Standards-

Pictured Above: Morehouse SCM-60 Aircraft and Truck Scale Calibrating Machine

**Using force instruments to
calibrate in mass has a similar measurement error**.

Forces are defined by
Newton’s second law of motion is expressed by F =kMA. Forces are not the same
as or can they be substituted for mass without correction. Phillip Stein
once wrote in his paper Gravity of the Situation, “Some measurements and
calibrations require knowledge of little g. Errors and uncertainties in little
g fall right to the bottom line (a 1% error in g results in a 1% error in the
force reported) and therefore exert an important influence on the correctness
of measurement results.”

A common example of
these measurement errors occurs with scales (a mass measurement
device). If 1000 lbs mass is used to calibrate a scale at Morehouse and
that scale is shipped to Denver, CO, it would have to be calibrated again or
corrected by formula to obtain the proper mass. Just comparing the gravity
in York (9.801158 m/s2) and Denver (9.79620 m/s2), we find a difference of
about 0.05 %. Without correction, 1000 lbs applied would read as 999.5
lbs. If the accuracy of the scale were 0.01 %, then the device would be at
least five times greater than the accuracy specification.

Converting Force to
Mass requires knowing the local gravity where the weighing takes place.

A mass correction
factor can be calculated to convert force to mass when the transfer standard is
used at a location where the gravity is known as follows:

Mass Correction Factor
= (9.80665/g)