# Why does Newton's second law involve mass?

Once one has learned of Electromagnetic force, they see that the amount of force experienced by particle given a field is proportional to the particles electric charge.

Similar situation the gravitational case where one sees that the gravitational force experienced by a particle is proportional to its mass.

But, if one sees the other side of the equation they see $$ma$$ for both cases, and further this $$m$$ is the exact same as the mass controlling size of gravitational force. Is there any deep reason why one side of Newton's second law ended up being $$ma$$ instead of say $$qa$$? ($$q$$ is charge)

It seems strange to me because we say gravity and electromagnetism are both fundamental forces but the 'factor' for gravity controls the actual acceleration caused on any particle by any type of force. Essentially, I am confused why mass seems to be more fundamental to calculating acceleration than charge.

• Does this answer your question? Is there a fundamental reason why gravitational mass is the same as inertial mass? May 18, 2022 at 0:00
• Tangentially related I guess
– Babu
May 18, 2022 at 0:04
• @Aplateofmomos Can you explain why it's not precisely the answer you're looking for? The $m$ which appears in Newton's 2nd law is called the inertial mass, while the $m$ which appears in Newton's law of gravity is called the gravitational mass. The fact that they are the same (or at least proportional) is a strange mystery in the context of Newtonian physics, but is explained beautifully in the context of general relativity. May 18, 2022 at 3:30
• @Aplateofmomos If this indeed does not capture the essence of your question, some clarification would go a long way toward helping somebody write a good answer for you. May 18, 2022 at 3:31
• this answer of mine might be relevant physics.stackexchange.com/questions/698224/… May 18, 2022 at 4:58