How to Calculate a Bungee Run Force

Measure the full length of the bungee cord with no tension on it. Divide inches by 12 to convert them to a decimal form. For example, if the length is 9 feet 10 inches, convert it to 9.8 feet.

Hook a 100-pound spring scale to the end of the bungee cord, and pull until the scale reads 50 pounds. Measure the total length of the cord for that reading. Do the same for 70 and 90 pounds. Convert values for inches to decimals. For example, if your measurements were 12 feet 11 inches, 14 feet 6 inches and 15 feet 10 inches, convert them to 12.9, 14.5 and 15.8.

Find the average length of stretch with the formula S = (y1 + y2 + y3)/3 - L, where y1, y2 and y3 are the lengths with tension, and L is the length without tension. For example, S = (12.9 + 14.5 + 15.8)/3 - 9.8 = 4.6 feet.

Calculate the average force with the formula F = (f1 + f2 + f3)/3, where f1, f2 and f3 are the three readings on the spring scale. With 50, 70 and 90 pounds, F = (50 + 70 + 90)/3 = 70 pounds.

Calculate the bungee cord's spring constant with the formula k = F/S. This formula comes from Hooke's law, which states that the force exerted by a spring is proportional to its extension. For example, k = 70/4.6 = 15.2 pounds/foot.

Have each contestant stretch their arms as far as they can, and measure from their fingertips to where the bungee cord connects to the belt or harness. Divide by 12 to convert inches to decimals. For example, if a contestant's reach is 43 inches, convert it to 3.6 feet.

Calculate the force of a bungee run with the formula F = (D - L - R)*k, where D is the total distance attained with the bungee marker, L is the length without tension (9.8), k is the cord's spring constant (15.2) and R is the contestant's reach. For example, if a contestant has a reach of 3.6 feet and he places the marker at the 27.5-foot mark, F = (27.5 - 9.8 - 3.6)*15.2 = 214.3 pounds.