A decathlon of questions on the physics of sport

Physics
Taken from the July 2021 issue of Physics World where it first appeared under the headline “Sporting chance”. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

With the Olympic Games due to get under way in Tokyo this month, Laura Hiscott brings you 10 physics-related sporting questions about the 10 different events in the decathlon – one of the highlights of the athletics programme. Answers will be revealed in a Physics World blog post next month, and you can give yourself a gold medal if you get them all right.

Day 1

100 m

In 1977 fully automatic timing, as opposed to timing done by people with stopwatches, became mandatory for world records in the 100 m sprint. Immediately after this change, average recorded times of sprinters increased slightly, before decreasing again. How did automatic timing cause this single stepwise increase?

Long jump

Many of the best long-jumpers in the world appear to continue running in the air as they cycle their legs for a few steps after take-off, in a technique called the hitch kick. What is the purpose of this motion?

Shot put

The women’s shot put has a mass of about 4 kg, but the volume varies slightly. If it can be made of solid iron or solid brass, what is the range of possible diameters it could have?

High jump

In the high jump, athletes traditionally keep their body upright as they kick their legs over the bar. But at the 1968 Olympic Games in Mexico City, American high-jumper Dick Fosbury won gold using a new technique he had developed. Now called the Fosbury flop, it involves slinking backwards over the bar and landing on your back. What physical principle does the Fosbury flop use to help an athlete clear a higher bar?

400 m

In the 400 m race, the starting line is staggered across lanes to ensure that all athletes have the same distance to run while staying in their lanes. Why does World Athletics say that the number of lanes for a standard track should be no more than nine?

Day 2

110 m hurdles

The men’s 110 m hurdle event has 10 hurdles spaced at 9.14 m from one another. The take-off foot should touch the ground at 2.1–2.2 m in front of each hurdle, and the athlete normally lands about 1 m from the hurdle. Most athletes take three steps between hurdles (not including the hurdle jump). About how long should each stride be?

Discus

The theoretical optimal angle for throwing an object as far as possible is 45 degrees to the ground. However, most athletes have an optimal angle slightly smaller. Why is this?

Pole vault

For an athlete with a centre of mass 1 m above the ground, who can run at 10 m/s, what is the theoretical limit to the pole vault height they can clear? And why is the pole vault world record slightly above this?

Javelin

In 1986 the men’s javelin was redesigned so that the centre of mass moved 4 cm closer to the tip. The women’s javelin was similarly redesigned in 1999. Which two problems prompted this redesign, and how did it solve them?

1500 m

The 2016 Olympic Games in Rio de Janeiro saw the slowest 1500 m Olympic event since 1932. Why is this event getting slower?

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