Physics - Fluid Question with Solution | TestHub

When a liquid drop falls slowly from a vertical glass tube, it detaches when its weight is just balanced by the upward force due to surface tension.

The surface tension acts along the circumference of the bore of the tube.

The circumference of the bore is $2\pi r$.

The upward force due to surface tension is given by $F=T\times 2\pi r\times \cos (\theta )$.

Given that the angle of contact $\theta$ is zero, $\cos (0)=1$.

Equating the weight of the drop to the surface tension force, we get $W=2\pi rT$.

Answer: $\mathrm{W}=2\pi \mathrm{rT}$