1. Need for Speed ----The Champion of The Track

2. Limitless world… Endless work…

3. Categorize 1.The athlete is the system. 2.When running, air does negative work, and the track does positive work, so the energy transfer can be E = Ek + Wair 3.Suppose the athlete’s mass is 70 kg, DA = 1 kg/m Getting down to business … F air F friction

4. For short-distance running race 4 Phases 1 . High acceleration phase 2. Low acceleration phase 3. Maximum velocity phase 4. Deceleration phase

5. Results… For a well trained sprinter, his vibration of his center of gravity in running is small. Just raise about 5cm Wu=mgh=70*10*0.05=35J Vaven is the average speed of the nth phase. D=1, ρ=1.2kg/m^3 , A=0.6m^2 Wairn=0.5*ρDAVaven^2 ΣWu=35J*40 W 1 =Wair1+ △ K1 =2801 J W2=Wair2+ Wu *22+ △ K2 =4688 J W3=Wair3+ Wu *13+ △ K3 =4688 J Wtot=ΣWair+ΣWu+(Kf-Ki)=12930 J P = Wtot/t= 1334W To improve the result by 10%, then the time is t’=8.72s Then Wtot’ =13249 J The extra energy △ W=319 J The extra power △P=185 W

6. Hurdling Conceptualize Because these are short-distance running races, the change of the height of his body could not be ignored. His body is lifted approximately 10cm per stride. Assume his body temperature does not change – neglect the internal energy. Kinetic energy and air resistance should be considered. When the athlete jump above the hurdles, the upper part of his barely moves. But his legs are lifted to the height of those hurdles.

9. Finalize To improve the result by 10%, the time of 110 m hurdle race will be 11.64s and 400m hurdle race 42.53s. Thus, the extra energy We 1= 1524 J The extra power P1’= (Wm1+ We 1)/t1’ — P1= 264 W From the result, we can tell that improving performance in these running races needs great efforts as well as special techniques, for it requires so much to improve. And here’s a graph which can approximately describe the relationship between distance and energy during the 110m hurdle race.

10. Thank you !