What is the primary function of air brakes in trains?

The primary function of air brakes in trains is to provide effective stopping power using compressed air. Air brakes operate by using compressed air to activate brake cylinders, which then apply pressure to the brake shoes against the wheels. This creates friction that slows down or stops the train efficiently. The use of compressed air allows for quicker and more reliable braking compared to other systems, making it a crucial component for safely managing the speed and stopping distance of trains, especially given their size and momentum.

While options that mention enhancing acceleration, supporting the train's weight, or improving traction may relate to other aspects of train operation, they do not accurately describe the fundamental purpose of air brakes. Acceleration is typically managed by the locomotives' engines, and the distribution of weight is managed through the train's design and suspension. Traction is influenced by factors such as wheel design and track conditions, not specifically by the braking system.