# Physics Java Labs

Before you start your lab report, it might be useful to look at a sample report.

## Lab: Archimedes' Experiment

• Purpose of experiment:
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 the experiment:
1. Run the java applet by clicking this button:

(It will open in a separate window).
2. 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.
3. 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 steps).
4. 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.
5. Measure the weight of each substance in air, in water, and in alcohol.
6. 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!)
7. 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 equations:
• The density of water is 1 g/cm3 = 1000 kg/m3
• 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 · g
• 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.