1 SX104 Week 8 Kinetics III Forces during walking, running and jumping Dr. Martine Deighan

2 Learning Outcomes Explain the direction of the vertical velocity and acceleration of the CoM during the preparation for a vertical jump. Know that Impulse = Change in Momentum and use this equation to calculate take-off velocity of a jump. Be able to label diagrams of force vs. time during walking, running and jumping. Know typical values of BWs for walking, running and jumping.

3 Vertical Jump

4 Start of Jump Accel = 0 Velocity = 0

5 Downwards Acceleration (speeding-up part of squat) AccelVelocity

6 Upwards Acceleration (slowing down to bottom of squat) Accel Velocity

7 Upwards Velocity Accel Velocity

8 Take-Off (just before toes leave floor, accel becomes –ve as the body’s upward motion begins to slow down: accel = m.s -1 once airborne) Accel Velocity

9 Force-Time Graph

10 Vertical Jump Velocity

11 Impulse = change in momentum Use this known relationship to calc. take-off velocity since v 1 = start velocity = 0 and v 2 = take off velocity Hence, take-off velocity is ______________by reducing the mass and increasing the Impulse (Ft). Impulse (Force x time) is the area under the force vs. time graph.

12 Impulse on Force-Time Graph NOTE: the impulse is only considered from the start of the movement, until the end of the movement, i.e. take-off.

13 Net Impulse +ve Area -ve Area

14 Landing Force in Vertical Jump

15 Forces in Stride Phases Drive Flight Landing Mid-stance

16 Forces in Walking Landing Support Drive Contact

17 Forces in Jogging

18 Forces in Sprinting Drive Contact Take-Off

19 Walk vs Run

20 Landing style in running

21 Walk vs run: braking and propulsive forces

22 Horizontal Impulse – how we can tell if someone is speeding up or slowing down Positive Horizontal Acceleration Negative Acceleration Zero Acceleration Negative impulse from landing phase Positive impulse from drive phase

23 Walk vs run: mediolateral forces

24 Reading Hall, pg. 395 – 399. Hamill and Knutzen, pg. 365 – 368 (the equations on these pages are not part of the learning outcomes for this lecture).