When a car is driving uphill at a constant speed, the RPMs (Revolutions Per Minute) of the engine increase due to a combination of factors related to the car's physics and the engine's power delivery.
Increased Load on the Engine: Going uphill means the car has to work against gravity to overcome the incline. This creates additional resistance, or load, on the engine. To maintain the same speed, the engine needs to provide more power to counteract this resistance.
Higher Gear and Torque: To handle the increased load, the car's transmission system may downshift to a lower gear. Lower gears provide higher torque, which is the twisting force that rotates the wheels. By downshifting, the engine can produce more torque at a given RPM, allowing it to cope with the additional load and maintain the desired speed.
Engine Throttle: In modern cars, the throttle controls the amount of air and fuel entering the engine. When driving uphill, the car's onboard computer may adjust the throttle position to supply more fuel and air to the engine, providing the necessary power to ascend the hill. This action increases the RPM to maintain the required power output.
Aerodynamic Drag: Uphill driving may also increase aerodynamic drag on the vehicle, as it needs to push through the air at a steeper angle. Aerodynamic drag increases with speed, and to maintain a constant speed against this additional drag, the engine must produce more power, leading to higher RPMs.
So, when driving uphill at a constant speed, the car's engine works harder to generate enough power to overcome the incline and maintain the desired speed. This increased workload results in higher RPMs.