Big trucks use air brakes, smaller vehicles use hydraulic brakes.
Air is supplied by an engine driven air compressor and stored in tanks on the tractor and trailer. When the brakes are applied the air comes from the tanks, they are then recharged by the compressor. Big trucks don't stop very well, when fully loaded they take about twice as long to stop as passenger cars. This has to due with current technology, it has nothing to due with the underlying physical processes. Some of these technological limitations involve the air brakes themselves, axles and tires are also a limiting factor however.