Comparing Drag in Still vs. Flowing Water: A Physics Experiment

In summary, the conversation discussed a physics experiment measuring drag on floating models with different variables. The models were placed in a flume tank and connected to a hanging bucket with pennies to immobilize it. The question of whether the drag experienced by an immobile object in flowing water is the same as a moving object in still water was raised, with the conclusion that there would be no difference as long as only the drag between the object and water is considered. The use of pennies in the experiment was clarified.
  • #1
BiteTheDust
8
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For a physics experiment, I'm testing the drag experienced by floating models with shape, wetted surface, and velocity as the independent variables.

I placed the models in a flume tank and connected them to a hanging bucket via a string that passed over a frictionless pulley (see attached pictures). By adding or removing pennies, I sought to immobilize the bucket in the air. Once this was achieved, the drag force of each model would then be the mass of bucket + pennies x gravity.

My question is can I safely assume that the drag experienced by an immobile object in flowing water is the same as the drag experienced by the same object moving through still water?

Thanks in advance for any feedback.
 

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  • #2


BiteTheDust said:
My question is can I safely assume that the drag experienced by an immobile object in flowing water is the same as the drag experienced by the same object moving through still water?

It is safe to assume that as long as you only consider the drag between the object and the water. A moving object would also experience wind resistance. Other than that there is no difference.

One thing I would like to point out is that the pictures seem to show that the pennies are being used to weigh down the object rather than to determine the drag its experiencing.
 
  • #3


Thanks for the response. I think I'm going to ignore the air resistance since it is relatively insignificant in the total resistance experienced by a moving object in water.

Oh and sorry for the confusion with the pennies. The pennies I am referring to are found in the bucket under the pulley (see the third picture I just uploaded).
In the second picture they are indeed use to weigh down the model and thereby increase the wetted surface of the models.
 

FAQ: Comparing Drag in Still vs. Flowing Water: A Physics Experiment

1. What is the purpose of this experiment?

The purpose of this experiment is to compare the drag force experienced by an object in still water versus in flowing water. This will help to understand the effect of water flow on the drag force and how it can impact objects moving through water.

2. How is the drag force measured in this experiment?

The drag force is measured by attaching an object, such as a sphere, to a force sensor and submerging it in both still water and flowing water. The force sensor will record the force exerted on the object, which is then used to calculate the drag force.

3. What variables are being tested in this experiment?

The variables being tested in this experiment are the water flow rate and the shape of the object. By changing the flow rate, the effect of different water speeds on drag force can be observed. Changing the shape of the object allows for a comparison of drag force on objects with different surface areas and shapes.

4. What are the potential sources of error in this experiment?

Potential sources of error in this experiment include variations in the water flow rate, inaccuracies in the force sensor readings, and disturbances to the water caused by the movement of the object. It is important to carefully control and calibrate these variables to ensure accurate results.

5. How can the results of this experiment be applied in real-life situations?

The results of this experiment can be applied in real-life situations, such as designing ships or submarines, where understanding the drag force is important for determining the speed and efficiency of the object in water. This experiment can also be relevant in sports, such as swimming, where minimizing drag can lead to faster times.

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