Isobaric process is a process where the pressure inside a system remains unchanged. In the Pressure Volume graph given, you can see that the pressure (y axis) remains constant with an increasing volume ( x axis). An example of this would be heating a container with a movable piston. Now, the degree of pressure is dependent on the frequency of collisions of particles inside a system on the walls. If this frequency changes, the pressure changes (proportionally). In our example, heating a container with a movable piston results in the particles inside the container to gain kinetic energy and move faster, meaning an increased frequency of collisions (higher pressure), but at the system time the increase in pressure results in the piston being pushed outwards, causing the volume of the container to increase. This results in decreased frequency of collision of the particles with the walls of the container (lesser pressure). This results in the a zero net effect on the pressure.
