# Can a fixed object in flowing water simulate an object moving through inert water?

1. Jun 17, 2011

### BiteTheDust

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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Last edited: Jun 17, 2011
2. Jun 17, 2011

### Dr_Morbius

Re: Can a fixed object in flowing water simulate an object moving through inert 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. Jun 17, 2011

### BiteTheDust

Re: Can a fixed object in flowing water simulate an object moving through inert water

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.