I just started watching the "Physics I: Classical Mechanics (Fall 2010)" course. In the first class, under the topic of measurement, the professor mentioned an object's acceleration being independent of its mass.

I get that larger objects need more energy to move, which could help explain part of this. What I do not understand is the other part - about the gravity of the falling object itself. I mean, does a pebble really fall as quickly as say another Earth sized object? (Assuming friction-less environment, no time dilation due to relative speed, etc) If it's a question of accuracy of measurement/scale, why wasn't this qualified?

Disclaimer: Taking these courses because I know enough to come to incorrect conclusions due to incomplete information, hence questions like this. I want formal training instead of picking up what I hear in casual conversations. I am aware this question probably comes off as immensely ignorant, hence my taking this course in the first place.

I don't have a full understanding of how this stress-energy tensor stuff works - so if basic physics assumes I understand the Landau–Lifpelletz pseudotensor and all that jazz before I start I'll need to find something even more basic.

Question

I just started watching the "Physics I: Classical Mechanics (Fall 2010)" course. In the first class, under the topic of measurement, the professor mentioned an object's acceleration being independent of its mass.

I get that larger objects need more energy to move, which could help explain part of this. What I do not understand is the other part - about the gravity of the falling object itself. I mean, does a pebble really fall as quickly as say another Earth sized object?  (Assuming friction-less environment, no time dilation due to relative speed, etc) If it's a question of accuracy of measurement/scale, why wasn't this qualified?

Disclaimer: Taking these courses because I know enough to come to incorrect conclusions due to incomplete information, hence questions like this. I want formal training instead of picking up what I hear in casual conversations. I am aware this question probably comes off as immensely ignorant, hence my taking this course in the first place.

I don't have a full understanding of how this stress-energy tensor stuff works - so if basic physics assumes I understand the Landau–Lifpelletz pseudotensor and all that jazz before I start I'll need to find something even more basic.

anonymous · Answer

F = ma
Acceleration (gravity) is constant if mass varies force on object changes.
More mass means less force and less mass means more force.