Next, stretch the cord to 3 meters long and measure the speed. Finally, stretch the cord to 5 meters and measure the speed. The speed increases as the cord is stretched. Theory says that the speed of the wave increases as the tension in the cord increases, and that it also increases as the mass per unit length of the cord decreases. As you stretch the cord you increase the tension and decrease the mass per unit length so that the speed definitely increases.
T is the tension in the cord.
Measure the mass of the cord, m, in kilograms then compute the mass per unit length. Measure the tension in the cord with a spring scale. To stretch our cords to 4 m requires 8 newtons of tension. If the tension were to double exactly, then the speed of the pulse would double. The pulse has to travel twice as far, at twice the speed, so the time remains the same.