These race cars run on gravity
LENOIR, N.C.—The sound of the countdown echoes across downtown Lenoir: “3,2,1, Go!”
This is immediately followed by the sound of clanging metal, as the gate at the end of a short ramp falls and two soapbox derby cars begin rolling down the Ashe Avenue hill.
The street runs through downtown and crowds on either side cheer as the drivers hunch down in their cars, trying to create a more streamlined shape. The cars fly past the crowds, the whirring sound of the wheels increasing in pitch the faster they go.
Welcome to the North Carolina Gravity Games, where science and gravity are fast and fun. The Earth’s magnetic pull supplies the power.
Ingenuity, engineering and physics combine to make the roughly 15-second run down the hill as fast as possible. This STEM-focused combination is one of the reasons Google founded the North Carolina Gravity Games in 2011. Now, seven years later, racers still have the opportunity to put their science chops to the test and, of course, have some fun.
“It has lots of science in it. And my friends come to cheer me on..." says 10-year-old Alexa Garner, one of the race car drivers. "You get to build the car, you get to learn to drive the car and go down the hill—it’s pretty fun.”
What it takes to compete in the ultimate engineering challenge
There are several divisions in the Gravity Games. The kits only division is essentially what the name says. Kit cars are already designed. A racer simply buys the “kit” from a manufacturer and assembles the car.
Then there's the engineered division, in which a racer can build a car however they want as long as the requirements are met.
The most challenging division is aptly called engineering challenge. Within this division, there's a new theme every year. This year was titled functional minimalism. The directive was to build a car that featured steering and brakes (always a good thing to include in a car), but that was also under a set weight limit.
“So we took the fold-out aluminum awning off of our recreational vehicle and used the bars to make the frame,” says David Alward, the father of one of the drivers competing in the engineering challenge. “And that worked well because it was all aluminum so it was lightweight. And then we folded everything together and put a folding seat and tires on it.”
Alward’s son, Joshua, is the driver. The family home-schools their children so the Gravity Games worked well as a science, math and engineering challenge.
Joshua explains in part how the car worked.
“The brace on the frame holds the steering bar, but the ball bearing inside allows it to turn and the bar attached to the steering bar with wires is how I control the car,” he says. The whole system is really basic, but it works.
“Actually, the steering worked really well and because I am so low to the ground the center of gravity is low so there’s not much risk of tipping over,” Joshua adds. Although he admits the system is pretty crude.
The cars entered in the Gravity Games reach speeds of about 20 miles per hour at the bottom of the hill. Joshua won his first two races, but the wide tires and lack of aerodynamic design finally caught up with him.
Not far from the starting gate, in pit row, a group of teens is huddled around their entry, trying to figure out where to put the hood ornament.
That’s right, the hood ornament. It’s a 3D-printed image of a catfish riding a unicorn.
This is one of three teams from Apex Friendship High School’s Academy of Engineering. Senior Jake Headle is using a zip tie to attach the decoration, which doubles as their mascot, to the steering column.
“The car works fine but the hood ornament is very essential to the car’s function,” says Headle.
“We were trying to figure out a mascot when somebody said, 'How about a catfish riding a unicorn?' And so I went home that night and drew it and the team loved it,” says senior Udayan Senapati.
“We have a single-seat assembly that’s composed of two-by-fours. Our axels are threaded rod through steel piping, so there’s no flex on the axels. Our wheels are 16 cart wheels, and then our steering is steel cable with a bar,” explains senior Sean Richicki, the designer of the car. “The only thing that is not homemade is the seat, which is from a friend’s Miata. We needed a seat and there it was!”
Diane Cadavid, the academy director, looks on as the mascot is attached.
“We love the engineering challenge division because it's an opportunity for kids to say, 'Let’s see if it will work and go figure it out,'" Cadavid says. “And the kids learn from that. And it’s okay when they fail because they can learn from that failure as well.”
Which physics factors govern the Gravity Games?
Apex Friendship’s entry did fine in the first race, but a more aerodynamically-designed car beat the team in the second race. So which laws of physics govern the Gravity Games and help determine the outcomes?
Before the race, as the car sits in the starting gate, it has potential energy. That’s the energy due to its position. Once the car starts moving, the energy becomes kinetic energy. That’s the energy of motion. The car accelerates.
Gravity is the strongest force on the track. Gravity pulls objects towards the center of the earth. It’s also what's pulling the car down the hill.
The car’s weight is the measure of the pull of gravity in pounds or kilograms. But it’s the car’s mass, or the amount of matter in an object, that’s most important. In this case, the mass includes everything in the car plus the driver. The higher the mass of the car, the greater the amount of potential energy at the start of the race.
Friction, or the force that resists the motion of two surfaces in contact, slows the car down. Wide tires, tires that wobble, and steering increase friction.
- Wind Resistance
There’s also wind resistance or drag. That’s the slowing effect air causes as the car moves through the atmosphere. The more aerodynamically a car is designed, the less drag.
The opportunity for diverse lessons in physics is why Google created the games. The company also runs a big data center in Lenoir.
“It’s a great way to get students engaged, excited and into a hands-on activity,” says Enoch Moeller, the site hardware operations manager for Google. “It’s not just classroom learning, which is important, but this is a way to bring it all together and see practical applications of physics, aerodynamics, gravity and the way everything works together.”
And if the racing encourages a few students to go into STEM careers?
"Then we have done our job and who knows, they may work for Google,” adds Moeller.
As for driver Alexa, for now, she keeps racing. In this race, she ended up winning and finished in third place. Besides winning, she also loves breaking stereotypes.
“So, what, I’m a girl driver,” says Alexa, with a fierce look of determination on her face. “Maybe it’s not all boys in this, girls can drive and beat you all.”
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