Is it possible to disregard drag force of water with no viscosity that affects lightweight pop-up ball (its weight is assumed to be zero)? There is a discussion, on which I consider that although weight is small, the influence of drag force does not depend on ball but on water, therefore this force must be taken into account. What can you say?
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In the situation you have described in the comment there is a drag force acting on a ball even if water is assumed to be inviscid. However, one should carefully calculate it in order to decide whether it matters at all. The effect responsible for the drag is called added mass. Actually I refer you to that wikipedia article to find out the explanation. What matters is whether this drag is strong enough for your case. The force should be $$\boldsymbol F = -\frac{1}{2} \rho_w V \boldsymbol a$$ where $\boldsymbol a$ is the ball's acceleration, $\rho_w$ is water density and $V$ is the ball's volume. So if the acceleration is comparable to $\boldsymbol g$ then the drag is comparable to the buoyant force and could not be neglected. Since you assume ball's density to be zero then you have to take the drag into account because otherwise it acceleration would be equal to g. |
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