KIN 330 Lab 3: Angular Kinematics

MAXIMUM: 10 POINTS

Objectives

• Understanding basic concepts of angular kinematics (angular displacement, angular velocity and angular acceleration)
• Understanding the relation between linear and angular kinematics

Instructions

• Please do your own work.
• Please only use the HW/Lab template Word document provided on D2L to submit your answers. This template consists of an answer table in the first page where you only have to list the answers. The second page consists of a “work table” where you have to show your work (or explain reasoning). If you have handwritten portions, take a picture (or scan the pages) and insert into the work table.
• Please be neat – I can only grade what I can read
• Submit the file as a PDF document on D2L., along with the associated Tracker files

StePS

1. Open the video bicep curl.MP4
2. Select the movement between the specified frames (Start frame: 113, End-frame:228)
3. Track the shoulder, elbow, wrist markers
4. Calibrate this video using the calibration frame in calibration_1.MP4 (long side of the object in the frame is 76cm).
5. Save the tracked data in a .trk file
6. *For this lab, it does not matter where you position the coordinate frame since we will only be measuring angles and velocities)

INSTRUCTIONS FOR Computing the segment angle (absolute) and joint angle (relative)

6. Compute the forearm segment angle (i.e. the absolute angle of the forearm relative to the x-axis (Hint: Use the tape measure tool to measure absolute angle and attach one end to the elbow and the other end to the wrist)
7. Compute elbow joint angle (i.e. the relative angle) throughout the motion (hint: the elbow angle is computed between the shoulder, elbow and wrist markers). (Hint: Use the Protractor tool to measure relative angle – the vertex will be the elbow, and the two ends will be the shoulder and the wrist)

QUESTIONS

1. What is the elbow angle at the instant of maximum elbow flexion? (from the protractor)
2. What is the forearm segment angle at the instant of maximum elbow flexion? (from the tape measure)
3. What is the range of motion at the elbow joint (i.e., the angular displacement) during the flexion movement? (consider only the elbow flexion part of the movement – i.e. from the start of the movement to the instant of maximum elbow flexion).
4. How far is the wrist from the axis of rotation (i.e., the elbow)? (Hint: There will be variation in the measurement of this length using the tape measure – use the “average” length across all the measurements)
5. Compute the “distance” (sometimes referred to as the arc length) traveled by the wrist during the flexion movement (Hint: you can use l = rθ, where θ is the angular displacement measured in radians)
6. What is the maximum resultant linear velocity of the wrist during the flexion motion? (you can use the “v” from Tracker to find the “resultant velocity” of the wrist. This is NOT the vx or vy which are the velocities along specific directions).
7. What is the direction of the wrist linear velocity when the forearm is horizontal to the ground during the elbow flexion movement – (i) upward, (ii) downward, (iii) toward the elbow or (iv) away from the elbow? (Choose one of the four options)
8. Compute the angular velocity of the elbow at the instant when the forearm is horizontal to the ground. (Hint: you can find out the velocity “v” from Q6 use v = rω to find out the value of ω; Do NOT use any values directly from Tracker )
9. Compute the
   • Centripetal acceleration experienced by the wrist at the time of maximum velocity? (Hint: a_c = v²/r or ω² r )
   • What is the direction of this centripetal acceleration – (i) upward, (ii) downward, (iii) toward the elbow or (iv) away from the elbow?

10. A goniometer is an instrument in a clinic that is also used to measure joint angles (see picture). What are the advantages and disadvantages of using video analysis compared to a goniometer?

Figure 1. A goniometer (from wisegeek.com)