Clumps grow into planetesimals by a. gravitationally pulling in other clumps. b. colliding with other clumps. c. attracting other clumps with opposite charge. d. conserving angular momentum.

In the early solar system, small clumps of matter exist. These clumps are often composed of dust grains and ice particles.
Over time, these clumps grow into larger bodies called planetesimals. One of the key mechanisms driving this growth is gravitational attraction.
Gravitational attraction occurs because every particle of matter in the universe exerts a force on every other particle. This force is known as gravity and is described by Newton's Law of Universal Gravitation.
According to this law, the force of gravity between two objects depends on their masses and the distance between them: }} Gravitational attraction leads to clump particles moving closer together. As these particles coalesce, they form larger objects. Over time, this process helps transform small clusters into significant planetesimals.

Another critical mechanism in the growth of planetesimals is planetary collisions.
During the early stages of solar system formation, space was filled with many small objects. These bodies often had intersecting orbits that led to frequent collisions.
When two clumps collide, they may stick together due to the forces involved in the impact. This sticking turns these smaller clumps into larger bodies.
The energy from the collision can cause some material to break apart, but many collisions result in net growth.
Collisions are particularly influential because they contribute to a chaotic but effective method of accumulating mass. While individual collisions may seem insignificant, over millions of years, they play a huge role in building substantial planetary bodies.

Accretion mechanisms refer to the various processes through which material clumps together to form larger bodies.
For planetesimal formation, the most important accretion mechanisms include:

• Gravitational Accretion: This involves the gravitational attraction between particles, drawing them together to form larger clumps.
• Collisional Accretion: As discussed, this involves collisions between clumps that cause them to stick together.

Other than these, there are processes like gas drag, which slows down particles in a gas-rich environment.
This reduced speed allows particles to collide gently, making it easier for them to stick together.
Understanding these mechanisms provides a clearer picture of how our solar system evolved from a cloud of gas and dust into the complex array of planets and other bodies we see today.