Name ______Team # ______Date: ______
Physics Lab: Biomechanical Arm-Instructions
Introduction:
Stability is an important concept in practical life. This experiment investigates the role of the bicep muscle in providing stability for the forearm when lifting (and holding) loads. In physics stability is achieved when both the net force and the net torque are zero. In equation form:
Fx=0 Fy=0 τ=0
Goals
When finished with this lab you should be able to:
· Draw extended Free-Body Diagrams (FBDs).
· Calculate the components of a force.
· Calculate torque.
· Check for conditions of equilibrium.
· Apply physics to situations involving body mechanics and stability.
Procedure
Materials
Biomechanical Arm apparatus: On the next page is a larger diagram with the parts labelled. Note that this picture is very similar to our models. Whereas the one on the following page has a few more differences, the parts are functionally the same. Also note that this picture shows the force meter and load mass installed properly on the apparatus. /1 Force meter, 1 50 g mass, 1 100 g mass /
When setting up the arm, you need to check the following settings:
· The string that goes over the pulley needs to be straight up and down in back. See the diagram at the right.
· The force meter must be connected to the arch that is closer to the pivot (elbow). This is to make the string (bicep muscle) very nearly parallel to the upper arm section of the model. With this configuration, the reading off the protractor for the angle of the upper arm from horizontal is the same as that for the bicep muscle.
· Notice a small divot or indent approximately halfway between the pivot (elbow) and the hand area of the forearm. This mark is the location of the center of mass. You must measure its distance from the pivot point on the model.
· The mass of the forearm is 106 g. Make sure to record this with your data as it will be necessary for doing your calculations.
Your task in the laboratory activity is to predict the bicep muscle force for three different configurations of the biomechanical arm and compare to what you measure. Additionally, you will compare the bicep muscle force necessary to maintain stability under these three different situations and apply your results to situations in real life.
Configuration 1:
· 50 g mass is in the hand
· Upper arm and bicep muscle are vertical.
· Forearm is horizontal
Configuration 2:
· 100 g mass is in the hand
· Upper arm and bicep muscle are vertical.
· Forearm is horizontal
Configuration 3:
· 50 g mass is in the hand
· Upper arm and bicep muscle are at an angle.
· Forearm is horizontal
For each configuration you will be measuring:
· R1: Distance between pivot and bicep muscle attachment location.
· R2: Distance between pivot and center of mass location of forearm.
· R3: Distance between pivot and center of load mass.
· Angle of forearm.
· Angle of Bicep muscle (same as angle of upperarm).
· Force of bicep muscle as read on force meter. Be sure to read the force scale. Look at the units and read the scale with force units. If you are not sure, ask.
Lab : Biomechanical Arm-Instructions
Phys114-Eyresrev su16page 3