Thread by @TifrArnab

Now that everyone finally knows about #javelin throwing thanks to @Neeraj_chopra1's phenomenal gold medal at the Olympics, it's time to look at some delightful #Physics trivia and history behind this beautiful sport! A lazy Sunday thread on the Javelin throw! #scicomm (1/n)

Observation 1: High school physics says "for max range, a projectile should be launched at a 45 degree angle". That's true only for launch & target at the same height! Here, launch ~2m above ground, target at ground + LOTS of aerodynamics -> optimal angle is ~36 degrees! (2/n)

Trivia: The Javelin throw is a rare event where the IAAF (now called @WorldAthletics) intervened to change rules to force throw distances to be REDUCED, as changes (based on physics!) such as hollow, designer cross section, surface texture... made javelins more aerodynamic (3/n)

History: Check YT for Uwe Hohn's 1984 "Eternal World Record" throw of 104.8m under the old rules. The Javelin flies almost flat at touch down! Flat throws mean it is tough to pinpoint landing distance + throws >100m mean usual stadiums not big enough! -> Rules change... (4/n)

Trivia: Uwe Hohn is Neeraj Chopra's coach! Hohn, only person to throw 100+m unfortunately never won an Olympic medal, because GDR (East Germany) boycotted the 1984 Summer Games... Such is history! (5/n)

Today the size, shape, minimum weight, center of gravity of the javelin, surface finish (no rough paint, dimples etc) and allowed throwing techniques are all regulated by the IAAF. The javelin must dip at all times in flight, tip must hit ground first. No flat throws! (6/n)

History: A bit dated, but this insightful graph from N. Linthorne (Ch. 12 in Materials in Sport Equipment, vol 2. Cambridge 2007) shows the progress in distance thrown with time, clearly shows e.g. the dip during WW2, uptick due to new design, dip due to new rules.. (7/n)

Note: Linthorne's plot shows not the WR or OR which could be an outlier due to some superhuman performance, but 10th best for the year, which would be a *very* good indicator of top level performance but more reliable than the "record throw" (8/n)

Physics: The flight is complex, but key concept is that the Centre of Gravity has to be ahead (4cm) of the Centre of Pressure. (CG - where weight acts down, CP - where resultant of lift+drag acts up) This ensures that the javelin keeps dipping and avoids "flat throws". (9/n)

This figure showing the forces and directions (from andreasmaheras.com/wp-content/upl…) might make it clearer (10/n)

Of course, there are a LOT of variables - right from the run up, angular momentum, release dynamics (speed, height, angle), the angle of attack, wind direction and speed, air temp and density, ... that determine the trajectory and final distance thrown. (11/n)

While most elite athletes may not care about the equations governing the motion, they have a masterly and intuitive understanding of the physics principles behind their sport, which is just so amazing! Congratulations again @Neeraj_chopra1 for inspiring us all! 👏👏 (12/12)