This makes the graph easier to interpret for people of different body weight. It also shows one very interesting feature. So, we can draw a line at 9.81 to indicate body weight. We call this method of scaling the forces according to body mass normalisation , a technique which is used a lot in biomechanics. Notice that the normalised load force rises above and falls below the body weight line.
Experiment Get in a lift and press the button to go up.
Press to go down. Body weight increases when there is an upwards acceleration on the body, and falls when there is a downwards acceleration. So, in normal gait, there must be an extra upwards acceleration of the body when the load curve is above the body weight line, and an extra downwards acceleration when the load curve is below the body weight line. In the section on kinematics , we'll see why we do this. University of Waterloo press, Ontario.