DEKALB — Way back at the 2012 Summer Games, U.S. women’s soccer star Megan Rapinoe was already making history.
Rapinoe bent a corner kick through a maelstrom of defenders and found the back of the net without the ball being deflected by anyone. It was the first time ever in the Olympics anyone had scored straight from a corner. It’s known as the Olimpico Goal.
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How was it even possible? Mike Eads is an associate professor in the department of physics at NIU. He was one of the two physics professors presenting at NIU’s STEM Cafe event “The Physics of the Olympics” ahead of the games starting July 23. Eads gave some scientific insight on how the gold medalist curved the ball.
“You actually get a difference in pressure due to this spinning and how the ball interacts with the air as it goes around it. And what happens is there’s a difference in pressure,” he said. “You get a high pressure on the bottom here, a low pressure on the top, so that actually creates a force pointing upward. So, this spinning can actually cause one of these lateral forces that can cause balls to bend.”
That force is called the Magnus Effect. It’s one of many concepts explored by Eads and fellow professor Jahred Adelman.
Speaking of spinning, Adelman talked about angular momentum.
“We’re going to think of it as momentum for objects that are rotating. So instead of velocity, which is just how fast an object moves, we have angular velocity, which is how fast an object rotates,” said Adelman.
Take 4-time Olympic champion gymnast Simone Biles for example. When she jumps from the mat, the combination of forces going up and then gravity pushing back down on her center of gravity causing the twist is called torque.
Much like a diver, she can tuck or extend her arms and legs in midair to control how she twists and flips.
“Because angular momentum depends on the distance to the rotation axis, and the orientation, if you change that mass distribution, you can actually change how something rotates even while conserving angular momentum,” he said.
Eads, an avid runner, also wanted to break down the science behind how a race is won at any given distance.
Newton’s first law says that an object at rest stays at rest and an object in motion stays in motion — unless acted on by an external force.
“So, if we have our sprinters at rest, and well, if they’re going to start moving, then there must be a force,” he said.
There are all sorts of forces at play. First, the force of the runner launching off the starting blocks, the equal force of the block then pushing them forward and the force of the runner’s foot hitting the ground with each stride.
We know that the runners don’t just stay in motion. Humans can’t run forever; the race must end. That’s because there are other forces at play. There’s wind resistance, friction, even friction in your body.
“It’s also important to remember that there is friction in the joints of your body. I think as we get older, we get more friction in the various joints of our body,” said Eads.
Shorter races require faster acceleration, which requires bigger muscles and more force exerted per step by someone like sprinter Usain Bolt, compared to a marathoner.
Initial, explosive acceleration and big muscles are less important in a marathon. The pace will be steadier, so runners are lighter and keep their bodies mostly level to conserve energy.
There are endless scientific concepts that can allow you to see the Olympics — and everyday life — in new ways. Eads and Adelman want people to know they can engage with physics to learn about the world around them — and it doesn’t take wildly complex mathematics to do it.
NIU holds Stem Cafe events either virtually or in-person every month.