Simulation of an Upper Limb II

There are four forces in the diagram, the joint reaction force on the shoulder (the two components of JRFs, JRFsh and JRFsv are labeled in red); the force that is exerted by the person’s deltoid muscle, Fdel (orange), the weight of arm and hand WA (blue) and the weight of ball Wbal. (green). As the angle of the arm and the weight of the ball change, the arrows show the differences in the directions and magnitudes of forces. Notes: The simulation is calculated based on a normally proportioned person. The weight of ball approximately acts on the hand, the end of the blue line.
Objectives:
  1. Find out how Fdel, JRFsh, JRFsv and JRFs depend on the mass of the ball.
  2. Observe how Fdel, JRFsh, JRFsv and JRFs change when the arm moves up and down; discover the easiest and most challenging positions for the person.
  3. Be able to relate the simulations to life experience and explain the results by applying the knowledge of equilibrium.

Teaching Notes

Instructions:

According to your investigation case, you can replace initial values of the weight and height of the person. Similarly, the position of the arm and the weight of ball can be changed with the slider bars. Once the input is set up, you can click “Calculate” button to obtain the values of each force and its lever arm.

Weight of the person WP= N.       Height of the person HP= m
      Θdel= 15˚
  Force   Lever arm
  Arm   WA= N.   LAA= m
  Ball   Wbal= N.   LAbal= m
  Deltoid   Fdel = N.   LAdel= m
  JRFs=N.

Creative Commons License
This work by Dan Liu and Matthew Burk is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.