Experiment 1 - Does DIY Zahn Cup work?

Temperature - t - (oC)	Dynamic Viscosity - µ - (N s/m2) x 10-3	Kinematic Viscosity - ν - (m2/s) x 10-6
0	1.787	1.787
5	1.519	1.519
10	1.307	1.307
20	1.002	1.004
30	0.798	0.801
40	0.653	0.658
50	0.547	0.553
60	0.467	0.475
70	0.404	0.413
80	0.355	0.365
90	0.315	0.326
100	0.282	0.294

Aim of Experiment: To find out if my DIY Zahn Cup #1 is able to measure viscosity of liquids accurately by trying it with water at 20ºC, which has a viscosity of 1.004 cSt. (Based on background research.)

Hypothesis: I should be able to calculate a viscosity of about 1.004 cSt if I keep the size of the orifice as close to the actual Zahn Cup as possible.

Materials needed:

- 2 styrofoam cups

- 1 transparent plastic container

- 1 measuring cup (44ml)

- 1 screwdriver

- 1 sheet of cardboard

- 1 ruler

- 1 pair of scissors

- 1 mathematical compass

- 1 stopwatch (times up to milliseconds)

- 1 string

- 1 calculator

Set-up:

Making cup holder

1. Using a piece of string, measure the circumference of the middle of the styrofoam cup by measuring the length of the string using a ruler.

2. Calculate the radius of the middle of the styrofoam cup using the circumference. (Circumference ÷ π ÷ 2)

3. Draw a circle with the calculated radius on the cardboard sheet using the compass.

4. Cup out the circle.

5. Measure the diameter of the transparent plastic container and make sure the cardboard sheet is larger than the diameter.

Making Zahn Cup # 1

1. Using a ruler, mark out a circle with diameter of 2mm [0.078 inch = 0.19812cm = 1.9812mm = 2mm (rounded off to nearest whole number)] on one of the styrofoam cups.

2. Using the screwdriver, poke the marked circle out to create a hole. Keep as close to the marking as possible.

3. Measure the diameter of the hole with the ruler to check if it is accurate. Re-do set-up if diameter of hole is more than 0.5mm off.

Experiment Set-up:

1. Place the cup holder on top of the transparent plastic container. (At the centre).

2. Place the Zahn Cup # 1 into the cup holder.

Experiment Procedure:

1. Using the measuring cup, measure 44ml of water.

2. Allow the water to reach the temperature of the air-conditioned room. (20ºC)

3. Use the thermometer to check the temperature of the water.

4. Pour the water into the Zahn Cup and start the stopwatch at the same time.

5. Stop the stopwatch when the continuous flow of water is broken.

6. Take down the timing up to milliseconds.

7. Repeat steps 1-6 4 times more for more accurate results.

8. Using the formula [1.1(time taken for water to flow from orifice – 29)], calculate the viscosity of water based on the 5 timings.

9. Calculate the average viscosity of the 5 values.

10. Check against the actual viscosity of water (1.004 cSt).

*Note: Should experiment fail (measured viscosity is more than 0.01 off the actual viscosity), repeat experiment once more, or check the orifice size of the Zahn Cup again.

Independent Variable: -NA-

Constant Variables:

1. Amount of water poured into Zahn Cup.

2. Size of orifice of Zahn Cup.

3. Temperature of water.

Dependent Variable: Time taken for the continuous flow of water through the orifice to stop.

Results:

Liquid (44ml)	Time (s)	Viscosity (cSt)
Water (20ºC)	29.84	0.924
	29.97	1.067
	29.98	1.078
	29.96	1.056
	29.82	0.902
	Average Viscosity	1.0054

Data Analysis:

From this experiment, I measured an average viscosity of water: 1.0054 cSt. The measured viscosity is only 0.0014 off from the actual viscosity. This margin of error may be due to human error made when starting and stopping the stopwatch.

Conclusion:

I conclude that the DIY Zahn Cup is effective in measuring viscosity of liquids as the measured viscosity of water is very close to the actual viscosity. This conclusion is valid only with the following assumptions:

1. The Zahn Cup will work as well with other types of liquid, and not only for water.

2. Human error in starting and stopping the stopwatch is minimal.