17
Important
: Do not use any screw that would intrude more than 8 mm into the
threaded hole. This could damage the internal electronics of the WDSS.
Mounting on a Ring Stand
The WDSS is designed to be mounted on a ring stand to allow force measurements
in several different ways. Use the rod included with the WDSS (9.5 mm diameter
rod, 15 cm long, with a hole in it). Insert a thumb screw through the hole in the rod
and into the end of the WDSS nearest the power connector. Tighten the thumb
screw.
Another option is to use the aluminum rod threaded into the end of the WDSS
nearest the power switch and then attach this rod to a ring stand via a right-angle
clamp.
WDSS with thumb screw WDSS with rod threaded into the end
Hand Held Force Sensor Experiments
The aluminum rod can be used as a convenient handle for holding the WDSS in your
hand for some experiments. Avoid large off-axis forces which may damage the
WDSS or the rod.
18
The Accelerometers of the WDSS
The WDSS on a bicycle for studying acceleration
The WDSS has a three-axis –6 to +6
g
accelerometer inside it. Using Logger
Pro
,
you can graph any of these components or calculate the magnitude of the net
acceleration. The accelerometer can be used for a wide variety of experiments and
demonstrations, both inside and outside the classroom. In the lab, the accelerometers
can be used on dynamic carts to study Newton’s laws and on rotating objects to
study centripetal acceleration. Outside the lab there are lots of possibilities from
automobiles to playground equipment to amusement parks. Many examples of
acceleration experiments are included in the Experiments section of this manual,
below.
How the Accelerometers Work
The Wireless Dynamics System contains a three-axis linear accelerometer with an
electronic interface. The accelerometers are fabricated at right angles to each other.
Each acceleration sensing unit is micro-machined in silicon with very thin “fingers”
carved in silicon. These fingers flex when accelerated. They are arranged like the
plates of capacitors. As the fingers flex, the capacitance changes. A circuit on the IC
monitors the capacitance and converts it into a voltage signal. The signal is filtered
and sent to the analog input of the WDSS. The acceleration reading from each of the
three axes is transmitted by Bluetooth to the computer or stored internally during
remote data collection.
Accelerations are normally measured in either meters per second per second (m/s
2
)
or
g
’s. One
g
is the acceleration due to gravity at the Earth’s surface, or 9.8 m/s
2
.
This accelerometer will measure accelerations in the range of –6
g
(–59 m/s
2
) to +6
g
(+59 m/s
2
) in each direction. This is a range of accelerations that the human body
handles well. Many collisions will produce much larger accelerations. In fact,
dropping the WDSS on a hard surface from even a few centimeters can produce
accelerations of a hundred
g
’s. The WDSS accelerometers will not be damaged by
accelerations up to 3000
g
’s.
