Physical Modelling Project Report

Introduction

In the realm of household chores, dishwashing is a daily task that often goes unnoticed. Yet, the choice of dishwashing detergent can significantly impact the efficiency and effectiveness of this chore. Surface tension plays a crucial role in this cleaning process. The surface tension of water, and how it is affected by detergents, can be explored through physical modeling.

Testing Objective

The objective of this project is to determine the force required to lift a surface tension ring just above the water's surface.

We aim to investigate the impact of different types of detergents on water's surface tension. This research will help identify the detergent that can most effectively reduce surface tension in water and, consequently, is the most efficient for dish cleaning purposes.

Testing Procedure

1. Set up the apparatus as described below:
   • Attach the force sensor to a clamp and secure the clamp to a retort stand.
   • Connect the GoLink USB connector to the force sensor and your computer.
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   • Position a lab jack just below the force sensor with a glass dish on top.
   • Attach the surface tension ring to the force sensor using a string.
2. Pour 100 mL of tap water into the glass dish using a measuring cylinder.
3. Ensure that the surface tension ring is parallel to the water's surface because the surface tension formula considers the force applied parallel to the liquid's surface.
4. Fully immerse the surface tension ring into the water by adjusting the lab jack.
5. Set the data logger to auto-scaling and record the force at this fully submerged state, ensuring the axis is set to continuous reading.
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6. Adjust the lab jack so that the surface tension ring is completely out of the water, and the water's meniscus is removed from the ring (Frmax).
7. Record the time and the force from the force sensor when the water is detached.
8. Repeat steps 4-7 two more times using distilled water and calculate the average force.
9. Repeat steps 4-7 three times for each detergent sample, using 2 mL, 4 mL, and 6 mL of detergent A, B, and C, respectively, poured into the glass dish using a pipette (1 mL).
10. Thoroughly clean the glass dish after each detergent use to prevent mixing with other samples.
11. Record all results and calculate the average force for each dishwashing liquid to minimize measurement uncertainties.

Analysis of Measurements (Tables, Graphs, Error Analysis)

Equation for Surface Tension

The surface tension (γ) can be calculated using the formula:

γ = Frmax / (4πr)

Where:

• γ = Surface tension
• Frmax = Critical force on the ring
• r = Radius of the ring

Surface tension decreases as the force required to pull the ring out of water (Frmax) decreases. Force is directly proportional to surface tension. The detergent that reduces surface tension the most is the most effective for cleaning dishes.

Analysis of Results

From the experimental results, it is evident that water exhibits the highest surface tension, as it requires the most force to separate the ring from its surface. When different detergent samples were introduced to the water, the force required decreased, indicating a reduction in surface tension. Among the detergent samples (A, B, and C), detergent C demonstrated the highest efficiency in cleaning dishes, as it resulted in the most significant reduction in surface tension.

Anomaly was observed in the data for detergent C (6 mL), with a force reading of 0.155226. This anomaly could be attributed to various errors, such as the surface tension ring contacting the glass dish, causing a delay in complete detachment. Additionally, there might have been difficulty in extracting precisely 2 mL, 4 mL, or 6 mL of washing liquid from the pipette, leading to inaccurate measurements. Furthermore, as the surface tension ring was removed from the water, some water was lost from the glass dish, causing a reduction in water level.

Summary of Results

The table above summarizes the average force measurements for each detergent sample at different concentrations.

The results suggest that detergent C was the most effective among the tested detergent samples because it significantly reduced surface tension. Different concentrations of each detergent were used to investigate the relationship between detergent concentration and surface tension reduction. It can be concluded that higher detergent concentrations result in lower surface tension.

Conclusions

The most effective detergent for dish cleaning is the one that reduces surface tension by the greatest amount. According to the surface tension formula, the most effective detergent is the one that requires the least force to separate the ring from the water. This property facilitates the removal of fat and dirt when cleaning dishes. Therefore, detergent C is the most efficient among all the tested detergents, as it requires the least force to detach the ring from the water.