In order to find the force of the wind from a fan, you might want a lever. So to use the lever, attatch the fan onto one side of the lever facing upward. Then, when the fan turns on the wind from the fan will blow up causing that side to go down which causes the other side to go up. then, put masses on the side that is up to try and even the surface out. Now that your lever is balanced, use the side with the masses on it to find out how many grams there is. So now you can use the scientific equation (N=1kg m)/s squared, where N is newtons, kg is kilograms, m equals meters, and s equals seconds. There are many ways to do this but this is the way that I found to do it.