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Gravity of the Games: Could athletes have advantage in Rio?

Posted August 17, 2016

Thiago Braz da Silva

While watching Olympic track and field events this week, I was reminded of a xkcd comic on pole vaulting. Could the nearly equatorial location of the 2016 Summer Games lead to new world records?

For the uninitiated, xkcd is a comic created by physicist Randall Munroe who worked at NASA's Langley Research Center as a programmer and roboticist before turning his hobby creating his “webcomic of romance, sarcasm, math, and language” into a full-time job.

xkcd #852, published on Jan. 26, 2011, pointed to variations in gravity of nearly 0.5 percent between different points Earth. He later calculated a 0.25 percent gravitational difference between London, site of the 2012 Summer Games, and Rio de Janeiro, providing a greater than 1 centimeter advantage in a 5-meter vault.

Without more information about the data and methods used to arrive at these figures, it is difficult to validate with any certainty, but Munroe is on to something here.

If Earth was a perfect sphere of uniform density, gravity would be uniform. However, bulges at the equator and varying topography and geology creates slight but measurable variations in the gravitational force pulling us toward the center of the Earth.

The Gravity Recovery and Climate Experiment (GRACE) mission has been orbiting Earth since 2002. GRACE measures variation in Earth’s gravity with great accuracy. Monthly datasets show global changes in distribution of water, both in the oceans and underground, and in geophysical changes. GRACE data allows climatologist to monitor glacial and sea ice loss and the resulting sea level rise. Hydrologists use the data to monitor drought and flood potential.

GRACE consists of two washing machine sized spacecraft, nicknamed “Tom” and “Jerry,” chasing each other about 300 miles above the Earth’s surface. “Tom” widens the gap as it overflies a denser portion of the Earth, “Jerry” closes that gap as it reaches that same spot. Separation between each is measured via a highly sensitive microwave ranging system providing very accurate view of about what lies beneath Earth’s surface.

GRACE data tells us that gravity was slightly higher than Earth’s average in London in August 2012, the mass equivalent of about 1 centimeter of water covering the city. Recent data from GRACE shows Rio de Janeiro with lower gravity, the mass equivalent of taking away about 15 centimeters of water covering the city. A 0.25 percent reduction in gravity fits pretty well here.

Ignoring all other factors, reducing gravity by a few tenths of a percent could conceivably add a centimeter or more in vertical height for a pole vaulter. These athletes don't operate in these simplified models, however.

Brazil’s Thiago Braz da Silva set an olympic men’s record at 6.03 meters on Monday, beating the current world record holder Renaud Lavillenie of France.

The women will take aim at the records on Friday.


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