- 1 How Will You Find The Center Of Mass Of The Forearm Boom 2 Using Figure 2 Write Down An Equation That Balances The 1 (19.66 KiB) Viewed 22 times
- 1 How Will You Find The Center Of Mass Of The Forearm Boom 2 Using Figure 2 Write Down An Equation That Balances The 2 (79.06 KiB) Viewed 22 times
Please note the following from Figure 1: The forearm (radius/ulna) in our mock up is a horizontal boom from E (elbow) to hand (h). The bicep muscle is a chain, with a force meter attached running from s (shoulder) to B (forearm). The elbow is a joint between the vertical metal rod and the horizontal boom. The point where the joint swivels is E in the diagrams above. Note that in our mock up, the rod does not end at E but extends past this point. You need to make sure you are measuring from the correct point when getting distances. We have excluded other muscles (e.g. triceps, etc.) which cause other torques on the "bones" in our system and the attachment points of the biceps are approximated. However, it is quite accurate for our needs. In order to calculate our torques, we must set a point about which we would rotate. In this system, we'll use the natural choice of the elbow, E. We choose this point because we cannot directly measure the forces applied here and since t = Frsin, any force applied at a distance of r = 0. provides no torque. We will calculate the components and net force on the elbow after we have satisfied that the system is not rotating. We need to define some distance measurements. We define them according to Figure 2. Every distance measured from our defined pivot point to any point on the horizontal boom is given as r with the appropriate subscript. For example, the distance from the elbow (E) to the center of mass of the horizontal boom (4) is r. The distance from the elbow (E) to the shoulder (s) is (, and the distance from the shoulder (s) to the horizontal boom through the chain (i.e. muscle) at point (B) is B h To keep our calculations simple, we will make the forearm horizontal such that gravity always pulls down at a right angle to the boom. If the upper arm is vertical, we have a right triangle SEB such that, + and sin = Figure 2-Defined distances used in this manual. Table 1: Determination of Uncertainties for Measured Values Uncertainty Every measurement you will make will have an uncertainty associated with it. We will determine the uncertainties of the measurements in the same ways as before (see Table 1). +1 in the last digit of the scale or the amount of fluctuation. We will take these values and find the propagated uncertainty for the forces and torques. +1 in the smallest increment of the ruler/meter stick or estimate of how well you can judge the size due to rounded edges. You will use the measured values to calculate the force of the muscle and compare it to the value given by the force meter. Student Determined E 15 Measurement Mass Distance Force meter