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Lecture Week 2 Linear Kinematics 1 EDU4SBM Sports Biomechanics Linear Kinematics Linear kinematics describes motion without regards to the force producing the motion. Usain Bolt 100 metres 9.69 2 EDU4SBM Sports Biomechanics Displacement Displacement occurs when a body changes its position. Displacement 120 100 80 60 40 20 0 0 2 4 6 8 10 12 Time 3 EDU4SBM Sports Biomechanics Velocity Average velocity is the rate of change of a body’s position with respect to time. 14.00 Velocity 12.00 10.00 8.00 6.00 4.00 2.00 0.00 0 2 4 6 8 10 12 Time 4 EDU4SBM Sports Biomechanics Distance and displacement Distance Displacement e.g. in a 400m race on a track the length of the path the athlete follows (distance) is 400m but their displacement will be zero metres (they finish where they start). 5 EDU4SBM Sports Biomechanics Speed and velocity Speed of a body is obtained by dividing the distance by the time taken Velocity is obtained by dividing the displacement by the time taken e.g. consider a swimmer in a 50m race in a 25m length pool who completes the race in 60 seconds -distance is 50m and displacement is 0m (swimmer is back where they started) Speed = distance/time Velocity = displacement/time 6 EDU4SBM Sports Biomechanics Acceleration Average acceleration is the average rate of change of a bodies velocity with respect to time. 5 Acceleration 4 3 2 1 0 -1 0 2 4 6 8 10 12 -2 Time 7 EDU4SBM Sports Biomechanics Question: Find the acceleration of a runner starting of with a velocity of zero (v1=0) and ending up with a velocity of 10 m/s (v2 = 10). This occurs in 5 seconds. Acceleration 8 EDU4SBM Sports Biomechanics 14 Velocity 13 Ben 1988 12 Carl 1988 11 Asafa 2005 Bolt 08 10 9 100 90 80 70 60 50 40 30 20 10 0 8 Displacement 9 EDU4SBM Sports Biomechanics Acceleration Acceleration is defined as the rate at which velocity changes with respect to time. average acceleration = (final velocity - initial velocity) ÷ elapsed time Acceleration due to gravity Whilst a body is in the air it is subject to a downward acceleration, due to gravity, of approximately 9.81m/s² 10 EDU4SBM Sports Biomechanics One of the most famous stories in science is about Galilo and the Leaning Tower of Pisa. Galileo supposedly reached out from an upper balcony and let fall two stones of different weights. A remarkable thing happened: to the gasps and amazement of the crowd below, the stones hit the ground together. Air resistance: stops an object accelerating forever 11 EDU4SBM Sports Biomechanics A cricket ball that has a mass of 0.2 kg has the same mass wherever it is ? Look at 3 different scenarios: 1) In Bendigo ? 2) On top of Mount Everest ? 3) On outer space ? Explain. The weight of a cricket ball is the same wherever it is ? Look at 3 different scenarios: 1) In Bendigo ? 2) On top of Mount Everest ? 3) On outerspace ? Explain. 12 EDU4SBM Sports Biomechanics Mass: the quantity of matter of which a body is composed of - not affected by gravity - measured in kilograms (kg) Weight: force due to gravity - is mass x gravity (9.81m/s²) 13 EDU4SBM Sports Biomechanics Conclusion All the principles of movement are based on how forces are made by the athlete or how they act on the athlete's body. They may appear complex at first but, as you learn the basics for each event, biomechanics and an analysis of movement will become an understandable and usable part of your coaching knowledge helping to make you a better coach. 14 EDU4SBM Sports Biomechanics