Physics 160 Biomechanics Lab Kinovea Lab 6 – Quantative Mechanical Analysis of Individual Performances Instructor: Dr. Julie Alexander Introduction: Listed below are the instructions for the physics calculations for your individual performances. Refer to your class notes on the analysis of Cheryl’s jump if you are required to calculate ground reaction forces and maximum height of a jump. If you are asked to compare two numbers then use the equation listed below. The quantity used to compare 2 numbers is called the percent difference, the formula is Percent difference 
(calculated value  measured value)
100% measured value
Procedure: Find your activity in the list below and follow the instructions for the calculations. Include these calculations in your group presentation. 1. Back tuck –Just like in class calculate the acceleration during the push off phase and the ground reaction force during this phase. How does this compare to Cheryl’s 1100 N ground reaction force during her jump? Also get the velocity of take off from Kinovea and then calculate the maximum height of your center of mass. Compare this to the measured height from Kinovea of your center of mass. 2. Swim start – Track the horizontal change in position of the hips to get the acceleration of the hips and then calculate the horizontal push off force during the time on the platform. The average push off force for national level swimmers is 350N. Compare your force to this. 3. Soccer kick – Track the ball while it is in contact with the foot to get the distance moved, and the velocity of the ball when it leaves the foot. From this calculate the acceleration of the ball while it is in contact with the foot. Then using the mass of the ball calculate the force on the ball due to the foot. If you can get the angle at which the ball leaves the foot use this and the velocity of the ball to predict the range of the ball while it is in the air. Use the formula for range on the formula sheet to do this calculation. How does this compare to the longest kick by an expert (you’ll have to look this value up on the internet) 4. Volleyball –Track the ball to find the velocity of the ball just after it is hit. Find the angle that it is hit at and use the formula for the range of a projectile to calculate the distance the ball will go after it leaves the hand. You’ll need initial velocity, height from ground at which the ball was hit and angle at which it is hit to calculate R. How long is a volleyball court? Will it go out of bounds? 5.
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Boxing punch – calculate the acceleration of the hand before it makes contact and then calculate the force using F=ma. Look in the back of the textbook to get an estimate of the mass of the arm. Use this for mass. How does this compare to the 1100N ground reaction force of Cheryl’s jump? This would be the force on your head if you lay down and let Cheryl stand on your head and then jump up off your head. Cartwheel – Measure the distance from hand to foot while in the handstand position and then find the time that the back foot is in the air. Use these values to find the linear and angular velocity of the back foot during the cartwheel. Do the same for the front foot, compare these two values? Deadlift – Calculate the torque about the hips due to the weight in your hands. Use Kinovea to draw a line diagram showing the line of action of the force and the perpendicular distance from the hips to the line of action. Measure these distances in Kinovea and use them to find the torque at the lowest position of the lift and then near the top of the lift. How do the torques compare? What muscles are producing the counterclockwise torques to balance these torques. Free throw – Calculate the ground reaction force during the preparation for the free throw. How does it compare to the 1100N ground reaction force of Cheryl’s jump? Basketball dunk – Just like in class calculate the acceleration of Michael Jordan during the push off phase of his jump and then calculate his ground reaction force during this phase. You’ll need to look up his mass. Also get the velocity of take off from Kinovea and then calculate the maximum height of his center of mass. Compare this to the measured height (from Kinovea) of his center of mass. Skating – Calculate the angular velocity of rotation for the jump. Express it in rad/s. Assuming that you could continue this angular velocity for another full rotation how long would you have to be in the air for to complete 2.5 rotations? Using this time in the air calculate the height that your center of mass would have to rise in order to have time to do the 2.5 rotations? Formula is H=9.8*(time in air)2 /8 Compare this height to Cheryl’s jump height of 23cm. Hurdling – a good hurdler will have her hips very close to the hurdle so she doesn’t lose kinetic energy to potential energy. Track the hips over the hurdle and find the horizontal velocity of her hips just before she leaves the ground and then again when her hips are at the highest point. Also find the change in height of her hips from the ground before the hurdle and then again on the top of the hurdle. Use conservation of energy to show that the loss of horizontal velocity is due to the gain in potential energy mgh when her hips are at the highest point.