Ross Chastain gave an excellent physics lesson in Martinsville. He managed to overtake five cars in the last half lap of the race.
Turning requires turning power
Imagine swinging a tennis ball attached to a string over your head. The ball moves in a circle due to the string.
This string provides a force that spins the ball. This turning force always points towards the center of rotation. Physicists call it “centripetal force” but I think “torque” is more meaningful.
Spinning on a race track uses exactly the same physical principle – just without a string.
And these 3,675-pound cars require a lot more torque than a tennis ball.
The force required to turn is proportional to the mass that is turning, times the speed, times the speed, all divided by the turning radius.
Physics tells us:
- Faster turns require more torque.
- Tighter turns (like Martinsville) require more torque.
- Heavier cars need more torque.
Let’s find out how much power you usually need in Martinsville. Pole speed was 96.078 mph, but each car’s speed varied during a lap.
- During practice, the cars reached 114-119 mph on the straights.
- Drivers cornered at 75-85 mph depending on driver and tire age.
- Most drivers slowed to around 60 mph before accelerating again to exit the corner.
Let’s say a driver takes Martinsville’s 202 foot radius turns and averages 80 miles per hour. That requires 7,775 pounds of torque.
The four tires have to apply all these almost four tons of torque.
Sir Isaac Newton discovered that force equals mass times acceleration. Chastain is 5’9”. I estimate his weight to be around 160 pounds. That makes the combined weight of the car and driver 3,675 pounds.
Dividing the force by the mass, the acceleration of a car spinning at 80 mph in Martinsville is typically about 2.1 Gs, where G is the acceleration due to gravity.
Your head, which weighs about 10 pounds, would feel like it weighed 20 pounds when subjected to 2G acceleration.
Compare that to astronauts on the space shuttle, who experienced about 3Gs on launch.
Rotatable model by Ross Chastain
On the final lap, Chastain had to overtake two cars. But none of the cars he had to pass were close enough to get to them.
Chastain made it into Turn 3. Rather than relying solely on the tires for turning power, Chastain used the wall to help him turn. This gave it enough torque to spin much faster.
Chastain’s lap time on Lap 499 was 20.758 seconds. His lap time on lap 500 was 18.845 seconds. As my colleague Dustin Long noted, that’s the fastest lap ever by a stock car at Martinsville Speedway.
Chastain rode normally for the first half of the lap. It would take about half the time of lap 499: 10.379 seconds.
He completed the last half of the lap in 8.466 seconds. He had to walk Average 180 km/h from the midpoint of the back straight to the start/finish line.
He didn’t run 112 miles an hour the whole distance. Let’s say he entered the corner at 122 mph, which would be 37-47 mph faster than anyone else. We’re talking 18,079 pounds of torque and nearly 5G acceleration.
Isn’t 5G dangerous?
A human can tolerate 5Gs for a short time. A 10 pound head would feel like 50 pounds under 5G acceleration. But that’s not the primary problem.
The human body is optimized for the 1 G acceleration of the Earth’s mass. When your body accelerates faster, it has to work harder to keep the blood circulating. Without adequate blood flow, the organs don’t get enough oxygen.
A warning sign of excessive G is loss of peripheral vision and the ability to see colors. When the brain senses a lack of oxygen, it shuts down the least important functions first.
But if the high acceleration continues, the person accelerating will eventually pass out. Fighter pilots wear pressure suits to ensure their circulation remains normal.
We owe much of what we know about how the human body tolerates high accelerations to Air Force Colonel John Stapp. Experimenting on himself in the 1950s, he survived 25G for just over a second and a peak force of 46.2G.
Unfortunately, his experiments permanently damaged his eyesight. However, he lived another 45 years and died in 1999 at the age of 89.
Not only did Ross Chastain make the Championship Four, he gave a great answer to any student who asks their math and science teacher: When am I ever going to use this?