Final answer:
Shifting to a lower gear causes the engine to slow down the rotation of the wheels, similar to using the brakes. This helps control the motion of the vehicle by increasing friction and reducing speed.
Step-by-step explanation:
When you shift to a lower gear while driving, it causes the engine to slow down the rotation of the wheels. This is similar to using the brakes, as it reduces the speed of the vehicle and can help to control its motion. Shifting to a lower gear increases the friction and resistance between the engine and the wheels, leading to a decrease in speed.
For example, when going downhill, shifting to a lower gear can help prevent the car from accelerating too quickly and potentially losing control. By reducing the speed through downshifting, the driver can effectively slow down the vehicle without relying solely on the brakes.