Raising a Flag

This week as I was driving home I realized that there are about ten United States flags within a mile of my house, and all of them are raised and lowered everyday. Why is it possible to raise these flags while standing on the ground? Pulleys of course, I've always answered myself, but in physics these past few weeks I have come to understand how and why a pulley works. In general, a pulley sits at the top of an object, in this case a flag pole, and has a rope on top of it, crossing to either side (in the case of a flag the ends of the rope are connected to make a circle so that the flag will slide straight up and down the pole, but

this has a minimal effect on the applicable physics concepts). In this case a flag is attached to one end of the rope and a person holds onto the other. In order to raise the flag the person must apply force to

his side of the rope. The application of this force creates tension in the rope. In order

to make the flag accelerate upwards, the tension in the rope must be greater than the weight (mass times gravity) of the flag (assuming that the rope has negligible mass). This can be explained by the equation net force=mass x acceleration. When the tension has overcome the weight of the flag, the flag will accelerate upwards until the person stops putting force on the rope, at which time their will no longer be tension on the rope and the flag will stop moving. Fnet=ma, 0=ma, a=0.