EXPERIMENT 1

                             Archimede's Principle

Demonstration of Archimede's Principle -- the buoyant force on objects in a fluid

1.Setup the force sensor in Channel A.

1.      Position the force sensor above the clear plastic container. Adjust the height so the hook on the bottom of the force sensor is located just above the top of the container.

2.      Press the tare button on the sensor to zero the force.

3.      Hang the cylindrical aluminum rod from the hook on the bottom of the force sensor.

4.      Fill the pitcher with water. This will be used to add water to the container.

5.      In the sampling options window, click Keyboard to set up data acquisition from the keyboard. Name the quantity to be entered from the keyboard to be "Depth" and define the units to be "cm". This quantity will be the depth of the rod submersed in the water.

6.      Open the Calculator window. Name a function "Fluid weight" with short name "Wf" and units "N" to calculate the weight of fluid displaced by the rod. Define it to be the Depth (in cm) multiplied by the cross-sectional area of the 1" diameter rod (5.07cm²), the mass density of water (1000 kg/m³), and the acceleration of gravity g (9.8 m/s²). Divide by 10⁶ to put the result in N.

7.      Name a second function "Object weight" with short name "W" and units "N" to be the measured weight of the object. This is just (-1) multiplied by the measured Force (channel A) -- the force sensor reads downward forces as negative.

8.      Open a table with columns for Depth (keyboard), Fluid weight (calculated), and Object weight (calculated).

Predictions: How do you predict that the weight of the aluminum rod measured by the force probe will vary as a function of the weight of the fluid displaced by the rod. Be as specific as possible.

How would this result differ if you used a plastic rod instead of an aluminum rod?

9.      Test your predictions. Start the data acquisition by clicking REC.

10.At the prompt, hit return to enter the depth submersed to be 0.0

     cm. This value will be entered in the Table, along with the

     calculated weights.

11.Pour water from the pitcher into the container until the level is

     1cm above the bottom of the rod.

12.Enter the depth. Ideally, this will be 1.0cm, but enter the actual depth.

12.Continue incrementing the depth in 1cm steps, until the object is fully submersed. For the last value, enter the total length of the rod.

13.Stop the data acquisition.

14.Remove the Aluminum rod from the force sensor and pour the water from the container back into the pitcher.

15.Repeat the experiment with the plastic rod. Since this object will float, insert the small section of clear plastic tubing into the eyelet at the top of the plastic rod to keep it from floating up.

ANALYSIS:

Carry out the following analysis for each of the rods:

1.    Make a graph of the Object weight on the vertical axis vs. the Fluid weight on the horizontal axis.

2.    Find the slope of the curve using the Statistics/Curve Fit/Linear fit. Compare to the predicted slope = -1.

3.    From the Object weight when fully submersed, determine the rod density.

4. Print a copy of the graph showing both samples. Then delete all data runs.

Questions: Did your results agree with your predictions?