1J30.25 - Forces on a String - Three Students and a Rope
Stretch the string between the two scales until a force of 70 Newtons shows on each scale. Add the 5 kg weight to the center of the string and observe the angle displacement and the force changes. Observe that no matter how much force is applied to the ends of the string a relatively small amount of weight applied to the center of the string will give an angular displacement.
Another version of this involves a large rope and three students. Have two large student grab the ends of the rope and by pulling hard, stretch it as straight as possible. The third, much smaller student then goes to the center of the rope and pulls at 90 degrees to the rope, easily pulling the two larger students toward each other.
The instructor may do this demonstration by themselves if they attach one end of the rope to a wall, and run the other end of the rope over a pulley and attach it to a very large weight. The instructor can pull at the center of the rope and easily lift the large weight.
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