An Engine Fueled by Gravity

In Lenoir, North Carolina, young derby drivers are putting their petals to the metal in a series of races in which their only engine is gravity. The downhill run teaches physics, as well as engineering, to students in a fun and creative way.


In Lenoir, North Carolina, young derby drivers are putting their pedals to the metal in a series of races in which their only engine is gravity.

The Downhill Run teaches physics as well as engineering to students in a fun and creative way.

Here's a look.

[ Speaks indistinctly ] And they're away!

Science and gravity are fast and fun...

All right, and they're off! the North Carolina Gravity Games.

[ Cheers and applause ] The Earth's magnetic pull provides the power.

Ingenuity, engineering, and physics combine to make the 15-second run down the Ashe Avenue hill in downtown Lenoir as fast as possible.

It has lots of science in it, and my friend's going to come with me and cheer me on.

And it's really fun.

[ Cheers and applause ]

They're away!

That's 10-year-old Alexa Garner.

She likes science.

All right! Come on!

I like doing experiments and stuff like that.

And for math, I just like all of the equations and everything.

She also likes racing in soapbox derby events.

You get to build the car, and you get to see how it works and everything.

And you get to learn how to drive the car, go down the hill, and it's pretty fun.

Alexa won her first race easily.

We'll check back with her.

These race cars are called kit cars.

A racer buys a kit of premade materials to build the car.

Well, it's really cool because the schools and teams and Scouts and home-school groups work on these cars throughout the year.

Then they come, and there's a little bit of pressure to race 'cause they haven't seen this hill before.

And then they have to tweak, refine, do some engineering.

You'll see some kids with some adjustable wrenches under their cars, tweaking them.

And they go race again, which is very much what the engineering process is in the real world.

But there's another division in the Gravity Games, called Engineering Challenge.

This year's theme was functional minimalism.

Oh, and across the line!

So to make a functional vehicle that had steering and brakes but would also make a weight limit, under a weight limit.

And this folding car was the Alward family's solution.

The family homeschools their children.

The Gravity Games provided a great learning tool.

We took an awning off of an RV.

It was just an awning that folded out, and the bars that held the awning up, we used those.

They're made out of aluminum.

And we cut those down and bolted everything together and put some tires on it.

The ball bearings stay still, but it can spin inside, so it gives it easy spinning.

Okay. And then your steering is just that bar -- you just pull the bar one way or another.

Yes, just pull this string right here.


No offense -- I would be a little nervous riding this because there's just not... much around you.

Here we go, and they're off!

But you feel pretty good.


Because the gravity, I sit low on the cart, so the gravity is really low to me.

I'm really low to the ground.

So I won't roll as easily.

Cars reach speeds of about 20 miles per hour.

Joshua won his first two races but then lost.

Wait. Wait.

Where do you want to put it?

[ Indistinct conversation ]

Right here.

Yeah, right there.

This is perfect.

And this is one of three teams from Apex Friendship High School's Academy of Engineering.

There was no problem with the car.

We've just got to find where to put our hood ornament.

It's very essential to the car's function.

There was one time we were trying to decide who our mascot was.

And someone randomly said, 'A catfish riding a unicorn.'

That was me, by the way.

Yeah, that was him.

A catfish riding a unicorn.

A catfish riding a unicorn.

It was random, out of nowhere.

So I decided to draw it that night, and I brought it the next day, and the team was in love with it.

Udayan here, he drew it, and then we got a vector of the image, and then we 3D printed it yesterday.

We have a single-seat assembly that's composed of 2x4s.

Our axles are threaded rod through grade-16 steel pipe.

And they're away!

And then our steering is just steel cable to the axle.

And then the seat looks like something, like a real seat from a car.

Yeah, the seat is from Tommy Hasting's Miata.

We love the Engineering Challenge division because it's an opportunity for the kids to say, 'I don't know.

Let's see if it's going to work, and let's go figure it out,' and learn from that, and we like it when they fail 'cause then they learn from that failure, and they move forward from that.

A more aerodynamically designed car beat the team in a second race.

So just what laws of physics govern the Gravity Games?

Well, before the race, every car has potential energy.

That's the energy due to its position.

Once the car starts moving, that energy becomes kinetic energy, 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 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, that's the car plus the driver.

The higher the mass, the greater the amount of potential energy at the start of the race.

And they're off!

Then there's friction, the force that resists the motion of two surfaces in contact.

That slows the car down.

Wide tires, tires that wobble, and even steering increase friction.

There's also wind resistance, or drag.

That's the slowing effect that air causes as the car moves through an atmosphere.

And they're racing!

The lower the profile of the car, the less wind resistance.

All those physics lessons are why Google created the Gravity Games.

The company runs a big data center in Lenoir.

It's a great way to get students engaged, excited, participating in hands-on activity, not just classroom learning.

Obviously, they need to do that, but the way to really make it tie in and get them like, 'I can do this, and I can see practical application of physics and aerodynamics and gravity and the way everything works together' is through an activity like this.

We thought it would be a great way to get students engaged, excited, and if we can, you know, point a student as a result of this, one or two of them decide to go into a STEM career field or degree program, we've done our job.

And they're away!

By the way, Alexa kept racing and winning and finished in third place.

She also loves breaking stereotypes.

I'm a girl driver, and maybe it's not all boys in this.

Girls can race and beat y'all.

Nice job! [ Chuckles ]