* Gravity: Gravity is the primary force causing a car to roll downhill. If the car is on a slope, gravity pulls it downward.
* Lack of Engine Braking: When a car is in neutral, the engine is not connected to the wheels. This means there is no engine braking to resist the force of gravity.
* Friction: While friction from the tires and brakes can help slow down a car, it's not enough to completely prevent rolling on a steep incline.
Why it may *seem* like a manual car doesn't roll:
* Slight Incline: If the incline is very slight, the rolling motion may be too slow to notice.
* Parking Brake: Most drivers will apply the parking brake when leaving a manual car in neutral, which prevents it from rolling.
* Transmission Design: Some transmissions may have a small amount of internal resistance that slightly reduces the tendency to roll, but it's not a guarantee.
Important Note: It's never a good idea to leave a manual car in neutral on an incline without engaging the parking brake. This is extremely dangerous and could lead to an accident.
