Understanding G-Force: A Guide to Calculating G-Forces

Watching astronauts launch into space highlights how rapid acceleration affects the body, often resulting in the iconic "g-force face." But what exactly is g-force, and how do astronauts manage to endure it?

What Is G-Force?

G-force quantifies rapid acceleration or deceleration, a phenomenon often encountered by astronauts, pilots, race-car drivers, and roller coaster enthusiasts. It is measured in units of g, with one g representing the standard gravitational force experienced on Earth's surface at sea level.

In essence, g-force serves as a method to contrast extreme acceleration—whether in space, air, or on land—with the everyday gravitational pull we feel. The acceleration due to gravity is 32 feet per second squared (9.8 meters per second squared).

Astronauts can endure up to 3 g during a space shuttle ascent, which is three times the gravitational force we experience on Earth. Meanwhile, aerobatic and fighter pilots may face 9 to 10 g during rapid maneuvers or sharp turns in their aircraft.

High G-Force and the Human Body

Exposure to high g-forces, even for brief periods, can lead to tunnel vision and, eventually, loss of consciousness (g-LOC) as the force drives blood away from the brain toward the lower extremities.

How do pilots and astronauts maintain consciousness when exposed to the intense g-forces during rocket launches or sharp aerial maneuvers?

Training in centrifuge machines, which simulate rapid acceleration, helps condition the body for high g-forces. Since tolerance levels can fluctuate, military pilots often perform warm-up sequences in the air to assess their readiness before executing complex flight maneuvers.

To counteract the effects of g-forces, pilots and astronauts wear specialized g-suits. These suits inflate with air or water when a specific g-force threshold is reached, compressing the legs to prevent blood from pooling and ensuring they stay conscious.

G-Force in Action: The Texas Motor Speedway

On April 29, 2001, CART (Championship Auto Racing Teams) officials called off a race at the Texas Motor Speedway after drivers reported dizziness following just 10 laps. The track's high speeds and tight turns generate forces nearing 5 g in certain sections.

At 5 g, a driver feels a force five times their body weight. For example, in a 5 g turn, 60 to 70 pounds (27 to 32 kg) of force pulls their head sideways. Let’s explore how to calculate the g-forces a car endures during a turn and how Champ cars manage to stay on the track under such extreme conditions.

Determining the g-forces acting on drivers is straightforward. All we need are the turn radius and the car’s speed. As per Texas Motor Speedway's Track Facts, the turns have a 750-foot (229-meter) radius. During practice sessions, cars reached speeds of approximately 230 miles per hour (370 kph).

As a car navigates a turn, it continuously accelerates, which is why you feel an outward pull when turning in a regular car. The acceleration is calculated by squaring the car’s velocity and dividing it by the turn’s radius:

Let’s break down the calculations:

Banked Turns

What keeps the car on the track under such extreme forces? The answer lies in the design of banked turns.

The turns at Texas Motor Speedway are banked at 24 degrees. While this banking doesn’t alter the g-force calculations for the driver, it’s essential for enabling cars to navigate such sharp turns at speeds of 230 mph.

Without banking, a Champ Car attempting a flat turn at 230 mph would lose traction and slide off the track. Traction depends on the weight applied to the tires—greater weight means greater grip.

Banked turns redirect a portion of the g-forces generated during the turn to increase the weight on the tires, enhancing traction. To determine how much of the g-force contributes to tire weight, multiply the g-forces by the sine of the banking angle.

With a 24-degree banking, 1.93 g contributes additional weight to the wheels. Additionally, a portion of Earth’s gravity (1 g) also adds weight to the tires: 1 g x cos24° = 0.91 g. Combined, 2.84 g (or 2.84 times the car’s weight) presses down on the car during the turn, ensuring it stays firmly on the track.

Downforce

The car’s aerodynamic design generates substantial downforce at 230 mph. Unlike airplane wings that create lift, a Champ Car’s spoilers act like inverted wings, producing downforce instead. This downforce, created by the front and rear wings as well as the car’s body, keeps the vehicle firmly pressed onto the track.

The downforce is remarkable—once the car reaches 200 mph (322 kph), the downward pressure is so strong that the car could theoretically drive upside down on a tunnel ceiling! In street-course races, the aerodynamic suction is powerful enough to lift manhole covers, which is why they are welded down before the race to prevent such incidents.

Combining the effects of downforce and g-forces, more than four times the car’s weight keeps the tires firmly on the track as it navigates a 24-degree banked turn at 230 mph.

Final Thoughts

Drivers endure extreme physical stress on tracks like this. The acceleration levels far exceed what most people ever encounter. For comparison, the space shuttle reaches only 3 g during liftoff. What’s even more remarkable is how long drivers withstand such intense forces.

The Texas Motor Speedway spans 1.5 miles (2.4 km), with a 2,250-foot (686 m) front stretch and a 1,330-foot (405 m) backstretch.

At 230 mph (337 f/s), drivers spend roughly 6.5 seconds on the front stretch before enduring nearly 5 g of force for another 6.5 seconds during the turn. The backstretch takes about 4 seconds, followed by another 6.5 seconds of nearly 5 g in the next turn.

Had the planned 600-mile (966 km) race occurred, drivers would have alternated between 5 g and near-zero g a staggering 800 times.