Car physics: what forces act on the vehicle and how they affect control

When you get behind the wheel, your car becomes subject to several physical forces at once - from the obvious gravity, pressing the car to the road, to less noticeable, but critical centrifugal forces in turns or aerodynamic drag at high speed. Understanding these forces not only helps you better control your car, but also explains many of the nuances of driving - why a car “floats” on a wet road, how to brake correctly on a downhill, or why Porsche 911 with a rear engine, it is prone to skidding.

In this article, we will analyze all the key forces acting on a vehicle, from static (weight, tire pressure) to dynamic (inertia, engine thrust). Let us pay special attention to how these forces interact with each other in real conditions: for example, how a change in the center of gravity when loading the trunk affects stability in turns, or why, when braking sharply on ice, not only the brake system, but also the laws of physics are triggered. The material will be useful to both beginners and experienced drivers who want to deeply understand the behavior of their car.

1. Gravity: Why the car won't take off (and how it affects control)

Gravity is a constant vertical load acting on the car through its center of mass (the point where the bulk is concentrated). For passenger cars, the center of mass is usually at a height of 0.5–0.7 m from the road, for SUVs it is higher (up to 1 m), and for sports cars it is lower (0.3–0.4 m). Stability depends on this: the lower the center of mass, the more difficult it is to overturn the car in a turn.

On a flat road, the force of gravity is distributed evenly across all wheels, but as soon as you lean (for example, on an uphill or downhill), the load is redistributed. On a steep climb (angle > 15°) to 70% weight may occur on the front axle, which impairs the traction of the rear wheels. That is why it is recommended to avoid sudden maneuvers on mountain serpentines - the risk of the rear axle skidding increases significantly.

• 📍 High center of mass: SUVs, minibuses, loaded vans. Prone to capsize on turns.
• 🏎️ Low center of mass: sports cars (Lotus Elise, Mazda MX-5). They hold the road better, but can “squat” on bumps.
• ⚖️ Weight redistribution: Under hard braking, weight shifts forward, increasing the load on the front suspension.

⚠️ Attention: If you carry a heavy load on the roof (such as a roof rack or a boat), the center of mass rises by 20–30 cm. This increases the risk of rollover at speeds above 90 km/h or when making sharp turns. Always check your mounts and reduce your speed by 10-15% of your normal speed.

2. Friction: why the wheels don’t slip (and when this happens)

Friction force between the tires and the road is the only thing that keeps the car from sliding uncontrollably. It depends on three factors:

1. Coating material: asphalt gives a coefficient of adhesion 0.7–0.9, ice - 0.1–0.2, wet leaves - 0.3–0.4.
2. Tire condition: worn tires (remaining tread depth < 2 mm) loses up to 50% grip on a wet road.
3. Wheel load: the more weight on the axle, the higher the friction force (therefore, when braking, the front wheels lock later than the rear ones).

When the friction force exceeds a limit (for example, during sudden acceleration or braking), the wheels begin to slip. This leads to:

• 🔥 Slipping when starting (especially on ice or gravel).
• ❄️ Skidding when braking on a slippery road.
• 🌀 Demolition in turns (when the car “does not obey” the steering wheel).

Fun fact: racing cars Formula 1 tires get hot 100–120°Cto increase grip. Under normal conditions, tire overheating (>60°C) leads to their destruction. Therefore, after a long drive at high speed (for example, on the highway), it is worth taking a break for 10–15 minutes to allow the tires to cool down.

3. Aerodynamic resistance: why at speed the car “presses” to the road

Air resistance force grows proportionally square of speed. This means that when the speed is doubled (for example, with 60 km/h up to 120 km/h) resistance increases in 4 times. For a passenger car this may mean:

• 🚗 Loss of power: at speed 130 km/h up to 60% engine power goes to overcome the air.
• 💨 Deterioration in handling: cross wind on the bridge can move the car 0.5–1 m.
• 🔥 Brake overheating: at high speeds they cool less well due to less air flow under the car.

Manufacturers combat aerodynamic drag with:

• 🪁 Spoilers and wings (increase downforce at high speed).
• 🚪 Closed wheel arches (y Tesla Model S drag coefficient Cx = 0.208 - one of the best in the world).
• 🔳 Active radiator grilles (close at high speed to reduce resistance).

4. Centrifugal force: why the car “flies” out of a turn

Centrifugal force - this is the same “force of inertia” that tries to push the car out of the turn. Its value depends on:

• Machine weights (the heavier, the stronger the inertia).
• Speeds (increasing speed by 2 times increases strength by 4 times).
• Turning radius (the sharper the turn, the more dangerous).

Formula for calculating centrifugal force (F):

F = m * v² / r
where:
m—vehicle mass (kg),
v—speed (m/s),
r — turning radius (m).

Example: Volkswagen Golf mass 1300 kg enters a turn with a radius 20 m at speed 50 km/h (13.9 m/s). The centrifugal force will be:

F = 1300 * (13.9)² / 20 ≈ 12,500 N (≈1.3 tons!)

To counter this force, engineers use:

• 🏁 Anti-roll bars (reduce body roll).
• 🔄 Brake force distribution systems (EBD), which brake the inside wheels when turning.
• 🎯 Wide tires (increase the contact patch with the road).

⚠️ Attention: On wet or icy roads, centrifugal force can exceed the traction of the tires, even if you are driving at the permitted speed. For example, on a circular motion with a diameter 30 m at 40 km/h and in icy conditions the risk of skidding is 80%. Always slow down early!

5. Engine Traction: How Power is Converted into Motion

Traction force - this is the force that pushes the car forward. It depends on:

• 🔧 Engine torque (measured in Nm).
• ⚙️ Transmission ratio (the “shorter” the gear, the greater the traction force, but the lower the maximum speed).
• 🛞 Wheel radius (larger wheels increase leverage but require more effort to rotate).

At low speeds (for example, when starting off), the traction force is maximum, but as it accelerates it decreases due to air resistance and inertia. Therefore, racing cars (Bugatti Chiron, Rimac Nevera) have multi-speed gearboxes (7-10 speeds) to maintain an optimal balance between traction and speed.

I wonder what electric cars (for example, Tesla Model 3 Performance) have instantaneous torque from zero rpm, so their traction force at the start can exceed similar gasoline cars by 1.5–2 times. This explains their record acceleration to 100 km/h for 3–4 seconds.

Make sure the clutch does not slip (for manual transmission)

Check tire pressure (should be 0.2 bar higher than recommended to improve grip)

Test acceleration on a flat road (measure time up to 60 km/h)

Listen to the engine for unusual noises (may indicate loss of power) -->

6. Inertial forces: why passengers are “thrown” forward when braking

Inertia is the resistance of a body to a change in its speed. In a car it manifests itself in three situations:

1. When overclocking: Passengers are pressed into their seats.
2. When braking: Bodies move forward (so seat belts are needed).
3. In turns: passengers are “pressed” against the side door.

Inertia depends on masses and acceleration. For example, during emergency braking with 80 km/h up to 0 for 3 seconds passenger mass 70 kg experiences strength:

F = m  a = 70 kg  (80,000 m/h / 3600 s) / 3 s ≈ 518 N (≈53 kg)

This means that an unbelted passenger “weighs” almost 1.5 times more when hitting the front panel!

To reduce the influence of inertia, modern cars use:

• 🛑 Seat belt pretensioners (trigger for 0.01 s before impact).
• 🪑 Active head restraints (prevents whiplash injuries to the neck).
• 🚗 Stability control systems (ESP), which brake individual wheels when skidding.

7. Practical tips: how to use knowledge of forces for safe driving

Understanding the physics of a car helps you anticipate dangerous situations. Here are some practical recommendations:

• 🔄 In turns: reduce speed before the entrance into the turn, not during it. Braking hard in a corner shifts weight forward and increases the risk of skidding.
• ❄️ On the ice: Avoid sudden steering movements. Smooth actions allow inertial forces to be distributed evenly.
• 🚚 When towing: Increase the distance to the car in front by 2 times. The inertia force of the trailer lengthens the braking distance.
• 💨 At high speed: Stay right on multi-lane roads. Crosswinds can unexpectedly move the car.

If you feel that the car is starting to slide (for example, the rear axle is skidding in a turn), remember:

⚠️ Attention: Do not press the brake under any circumstances! This will only make the skidding worse. Instead:

1. Reduce the gas slightly (but do not release the pedal suddenly).
2. Turn the steering wheel towards the skid (if the rear skids, the steering wheel goes in the same direction).
3. After stabilization, level the steering wheel and gradually add gas.

FAQ: Frequently asked questions about forces acting on a car

E = 0.5  m  v²
where m is mass, v is speed.