Experiment 6 – Number of oscillations pendulum completes in liquids of different viscosities

Aim of experiment: To find out how number of oscillation the pendulum completes differ when it is placed in liquids of different viscosities.

Hypothesis:

As stated in my summary of research, viscosity is a measure of the resistance of a liquid to flow, or in other words, the friction against flow. Thus, the more viscous the liquid, the more friction it should have against flow. Therefore, the number of oscillations the pendulum completes in water (viscosity 1) should be the highest number as the pendulum will lose less energy through friction; while the number of oscillations the pendulum completes in honey water (viscosity 30) should be the lowest number as more energy will be lost to overcome friction, resulting in the least number of oscillations.

Materials Needed:

- 1 litre of water (viscosity 1)

- 1 litre of honey water (viscosity 10)

- 1 litre of honey water (viscosity 20)

- 1 litre of honey water (viscosity 30)

- 1 pendulum

- 1 measuring beaker (1 litre)

Experiment Procedure:

1. Fill the measuring beaker with water till it reaches the 1 litre mark.

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

3. Use the thermometer to check the temperature.

4. Position the chopsticks above the beaker such that the pendulum (string included) is fully submerged.

5. Raise the pendulum till it is just touching the surface of the water.

6. Release the pendulum.

7. Count the number of complete oscillations the pendulum makes.

8. Repeat the experiment 4 times more for more accurate results.

9. Repeat steps 1-8 with honey water (viscosity 10,20,30) instead of water.

Independent Variable: Viscosity of liquids the pendulum moves through

Constant Variables:

1. Amount of mixture poured into beaker (1 litre).

2. Length of string of pendulum.

3. Weight of pendulum.

4. Temperature of liquids tested.

5. Height to which pendulum is raised to before release.

Dependent Variable: Number of complete oscillations made by the pendulum before coming to a stop.

Results:

Liquid	Viscosity	No. of Oscillations
Water (20ºC)	1	5
		6
		5
		5
		6
	Average no. of oscillations	5.4
Honey Water (20ºC)	10	4
23% Honey		5
77% Water		5
		5
		4
	Average no. of oscillations	4.6
Honey Water (20ºC)	20	3
49% Honey		3
51% Water		4
		4
		4
	Average no. of oscillations	3.6
Honey Water (20ºC)	30	2
74% Honey		2
26% Water		2
		3
		2
	Average no. of oscillations	2.2

Data Analysis:

The honey water with viscosity of about 30 resulted in the shortest number of oscillations while water with viscosity of about 1 resulted in the most number of oscillations completed by the pendulum. The number of oscillations completed decreased as the viscosity of the liquids increased.

Conclusion:

The more viscous the liquid, the less number of oscillations the pendulum completes before coming to a stop. This conclusion is valid only with the following assumption:

1. The pendulum was raised to the same height before release, and there was no external force acting on it.