Land speed record cars reach velocities so high that slowing down is as challenging as speeding up. At extreme speed, the vehicle has enormous kinetic energy, and that energy must be removed safely without flipping, skidding, or overheating the brakes. Engineers use staged braking because no single system works well across the full speed range.
The goal is to keep the car stable while reducing speed over several kilometers of runway or salt flat.
Key Facts
- Kinetic energy increases with the square of speed: KE = 1/2 mv^2.
- At 1000 km/h, a 7000 kg car has about 270 MJ of kinetic energy.
- Aerodynamic drag force is approximately Fd = 1/2 rho Cd A v^2.
- Parachutes are most effective at high speed because drag increases with v^2.
- Braking work equals energy removed: W = Fd, where d is stopping distance.
- Wheel brakes are saved for lower speeds because friction limits and heat buildup are severe at extreme speed.
Vocabulary
- Kinetic energy
- The energy an object has because of its motion, equal to 1/2 mv^2.
- Aerodynamic drag
- A resistive force from air that acts opposite the direction of motion and grows rapidly with speed.
- Parachute braking
- A braking method that uses a deployed fabric canopy to create large aerodynamic drag behind the vehicle.
- Air brake
- A movable panel or surface that increases drag by pushing against the airflow around the vehicle.
- Wheel brake
- A friction or hydraulic braking system that slows the wheels and converts motion energy into heat.
Common Mistakes to Avoid
- Treating braking force as constant at all speeds, which is wrong because aerodynamic braking depends strongly on speed and changes throughout the run.
- Using wheel brakes first at extreme speed, which is wrong because the tires and brake materials may overheat, lose grip, or fail under huge loads.
- Forgetting that kinetic energy depends on v^2, which is wrong because doubling speed means four times as much energy must be removed.
- Ignoring vehicle stability during parachute deployment, which is wrong because uneven drag or sudden forces can yaw the car or make it difficult to control.
Practice Questions
- 1 A 7000 kg land speed car slows from 1000 km/h to 500 km/h. Calculate the kinetic energy removed during this speed reduction.
- 2 A parachute produces an average braking force of 60,000 N over 2500 m. How much energy does it remove from the car?
- 3 Explain why a land speed record car uses parachutes and air brakes at high speed before relying heavily on wheel brakes at lower speed.