Physics Java Labs
Before you start your lab report, it might be useful to
look at a sample
- Purpose of
In this lab you will devise your own method of measuring
the density of unknown materials. There are two
substances of different type in the lab to choose from.
You will also measure the density of alcohol.
- Instructions for performing
- Run the java applet by clicking this
button:(It will open in a separate window).
- You can select the sample substance (1 or 2) by
selecting it with the radio buttons. The sample hangs
from a beam that is balanced on the pyramid shaped
support in the middle. Above the sample, there is a
Newton-meter (to measure the force) connected to the
beam. However, the Newton-meter is not calibrated, and
so it will only show you if the net force is upward or
downward or close to 0. You can see this by the
position of the blue needle on the device. If the blue
needle point exactly upwards, then the force is close
to 0, and its deviation from the vertical is a measure
for the force.
- You can generate a counter force that balances the
weight of the sample by shifting the counter-weight on
the right side of the beam left or right. This can be
done by mouse-drag or using the left and right arrow
keys on your keyboard. The value of the counter force
is read out in the window in the upper right corner.
Each time you press the arrow keys the force changes
by 0.1 N. If you hold the shift key down at the same
time, you can make fine adjustments (0.02 N
- By balancing the counter force so that it exactly
cancels the weight of the sample, you can get the
needle on the Newton-meter to point exactly vertical.
The indicated value of the counter force is then the
weight of the substance.
- Measure the weight of each substance in air, in
water, and in alcohol.
- Devise a formula to extract
the densities of both substances
and that of alcohol as well as the volume of each
substance. Carefully write out the steps that
lead you to your findings and record your final
answers. If you can, include a discussion of the
measurement uncertainties and possible errors in your
extracted numerical values.
(On the positve side: there are no spreadsheets to
operate or plots to produce for this report!)
- Finally, write the report with your favorite word
processor or text editor and email it (as email
attachment) back to the instructor.
- Helful hints and
- The density of water is 1 g/cm3 = 1000
- Density = mass / volume:
r = m / V
- Weight in air = mass * gravitational acceleration:
Wair = m · g
- Bouyant force = weight in air - weight in liquid =
rliquid · V
- The volume displaced by the sample is the
same in both water and alcohol. If the glass
beakers are shifted to the up position, the samples
are completely submerged.
- The value of g = 9.81 m/s2.