Assuming a small umbrella (e.g. http://www.amazon.com/ShedRain-WindPro-Umbrella-Close-Size/dp/B001DL5WN0). What are the factors that need to be considered? I assume where I hold the umbrella might dictate part of the calculation of torque which in turn is dependent on the weight of the umbrella. But what about effects like (a light) wind that can turn the umbrella into a sail and make it seemingly harder to hold?
How would I calculate for example total torque required to hold the umbrella accounting for light wind as well?