ma = mg question

[mintchip_]

my little brother's scratching his head over physics, specifically why ma equals mg.

He's like, 'If my 75kg body weighs 735N on a scale (75 * 9.8), and something 75kg accelerating at 9.8 also means 735N of force... then obviously ma = mg. I know it's because we're on Earth, and it'd be ma = mg on the Moon too if everything's relative to Moon gravity.

But seriously, am I missing something in why ma and mg are basically the same here?
If mg represents the constant force of gravity pulling an object down, what circuit component or condition provides a constant "force" (or voltage) regardless of the load?

He's genuinely stumped and I wanna help him figure it out

 

[laylapot]

@mintchip_ Hahaha well, he's not wrong thinking ma = mg on Earth at rest, but that only works because g is the local acceleration. Once you leave constant gravity or start changing direction, ma and mg are no longer interchangeable. Is it understandable enough or should I explain simpler?

 

[mich4el.crx]

my little brother's scratching his head over physics, specifically why ma equals mg.

He's like, 'If my 75kg body weighs 735N on a scale (75 * 9.8), and something 75kg accelerating at 9.8 also means 735N of force... then obviously ma = mg. I know it's because we're on Earth, and it'd be ma = mg on the Moon too if everything's relative to Moon gravity.

But seriously, am I missing something in why ma and mg are basically the same here?
If mg represents the constant force of gravity pulling an object down, what circuit component or condition provides a constant "force" (or voltage) regardless of the load?

He's genuinely stumped and I wanna help him figure it out

The reason why ma and mg seem to be the same thing is because gravity is an acceleration. Specifically, g is the acceleration due to gravity on Earth, which is about 9.8 meters per second squared, like you mentioned.

The force of gravity is defined as mass times this acceleration. Newton's second law says that force equals mass times acceleration. When gravity is the only force acting on an object, like during free fall, the net force is the force of gravity. This is why all objects fall at the same rate, regardless of their mass, of course ignoring air resistance.

In circuits, a component that provides a constant voltage regardless of the load is a voltage source. An ideal voltage source will maintain a specific voltage across its terminals no matter how much current is drawn. A good real-world analogy is a battery, which provides a relatively constant voltage until its charge is depleted. I hope I'm explaining this well!