1. Gravitational force: This is the force that attracts particles towards each other due to their masses. In a nebula, the gravitational force is responsible for pulling the particles together to form clumps and eventually, stars.
2. Radiation pressure: This is the force exerted on particles by the electromagnetic radiation emitted by stars. Radiation pressure can push particles away from stars and help to disperse the nebula.
The balance between gravitational force and radiation pressure determines the structure and evolution of a nebula. If gravitational force is stronger, the nebula will collapse and form stars more quickly. If radiation pressure is stronger, the nebula will be dispersed and star formation will be inhibited.
