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M o d e l N o . M E - 9 5 0 2 E x p . 1 : H o o k e ’ s L a w — M e a s u r i n g F o r c e
0 1 2 - 1 2 8 7 6 B 11
Exp. 1: Hooke’s Law—Measuring Force
Equipment Needed
Introduction
At a practical level, a force is simply a push or a pull. A force is also a
vector quantity that has magnitude (size) and direction. There are dif-
ferent ways to apply and measure a force. One way to apply a force is to
hang a known mass, and determine the force based on the assumption
that gravity pulls the mass downward toward the center of the earth
with a magnitude
F = mg, where m is the known mass and g is the
acceleration due to gravity (9.8 m/s
2
). Note that the value of g can also
be expressed as 9.8 N/kg. Another way to apply a force is to pull with a
spring. A spring stretches when it is pulled, and if he amount it stretches
is directly proportional to the applied force, then the spring can be cali-
brated to measure unknown forces. In this experiment you will use the
known force associated with gravity pulling on calibrated masses to
investigate the properties of the Mounted Spring Scale.
Hooke’s Law
Hooke’s Law describes the relationship between the amount of force
and the amount of stretch for an “ideal” spring. The law states that the
force and the stretch are directly proportional. In other words, the ratio
of the force divided by the stretch is a constant,
k . The constant is called
the “spring constant”.
Setup
Place the Spring Scale on the Statics Board so that the spring hangs ver-
tically in the tube. Do not hang anything on the bottom hook. The indi-
cator must be aligned with the zero mark on the label. To zero the
Spring Scale, loosen the thumbnut at the top of the scale. Turn the top
hook clockwise to lower the indicator, and counter-clockwise to raise
the indicator. Once the indicator is aligned with the zero mark on the
label, tighten the thumbnut.
Procedure
1. Attach a thread to the bottom hook and hang a mass hanger from the thread.
2. Add mass to the mass hanger until the indicator is aligned with the 10 mm mark on the label. Adjust the mass
so that the indicator is as close as possible to the mark. Estimate the uncertainty in your measurement. (If you
add or remove 0.5 g, can you see a change? What happens if you add or remove 1 g or 2 g?)
3. Record the total amount of mass (including the mass hanger) in the data table. Record the uncertainty.
4. Add more mass to the mass hanger until the indicator is aligned with the 20 mm mark on the label and record
the total amount of mass and the uncertainty.
5. Repeat the process to move the indicator down by 10 mm each time until the indicator is aligned with the 80
mm mark. Record the total mass and the uncertainty each time.
Item Item
Statics Board Mounted Spring Scale
Mass and Hanger Set Thread
Top
hook
Thumbnut
Indicator
Zero
mark
Bottom
hook
Figure 1.1: Setup and Procedure
Mass
hanger
10
mm
Thread