Final answer:
Collisions between particles inside the walls of a raft result in the reversal of momentum, applying force to the walls and causing increased pressure in direct correlation with the number of collisions.
Step-by-step explanation:
When collisions occur between the particles inside the walls of a raft, the component of the particle's momentum that is perpendicular to the wall gets reversed, causing a force to be applied to the wall. This force is what leads to pressure within the container or raft. An increase in the number of gas particles leads to more collisions and consequently a greater force applied to the walls, which means increased pressure, according to the ideal gas law. This ties in with Newton's third law, indicating that for every action, there is an equal and opposite reaction, so the force on the particles is matched by the force on the container walls.