Two object run together to the earth despite of their mass

  • Context: High School 
  • Thread starter Thread starter Hepic
  • Start date Start date
  • Tags Tags
    Earth Mass
Click For Summary

Discussion Overview

The discussion revolves around the question of why two objects of different masses fall to the Earth at the same rate, exploring concepts related to gravity, force, and acceleration. Participants engage in clarifying misconceptions and discussing the implications of mass on gravitational acceleration, with references to both theoretical and practical considerations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that all objects fall with the same acceleration regardless of mass, emphasizing that this acceleration is independent of mass.
  • Others argue that the force of gravity is proportional to the mass of the object, leading to a cancellation of mass in the equations of motion, resulting in the same acceleration for different masses.
  • A participant explains that while a larger object experiences more force, it also has more inertia, which balances the effects and results in the same acceleration for both objects.
  • Concerns are raised about the applicability of these principles on different celestial bodies, such as the Moon, where gravitational acceleration differs from that on Earth.
  • One participant questions how the Earth "knows" to exert more force on a more massive object, leading to a clarification that the Earth does not have awareness and that the simplifications used in calculations assume the Earth as a fixed object.
  • Another participant notes that if the masses involved are comparable to the mass of the Earth, the simplifications may no longer hold true, indicating a need for a different approach in such scenarios.

Areas of Agreement / Disagreement

Participants generally agree that objects of different masses fall at the same rate under Earth's gravity, but there is disagreement on the terminology and implications of force and power in this context. The discussion remains unresolved regarding the effects of larger masses and the conditions under which the established principles apply.

Contextual Notes

Participants highlight that the discussion involves assumptions about the fixed nature of the Earth and the simplifications made in gravitational calculations. The implications of mass on gravitational effects are noted to vary under different conditions, such as when masses are comparable to that of the Earth.

Hepic
Messages
118
Reaction score
0
Everybody knows that two object run together to the Earth despite of their mass. For example we have a object with 30 kg and one with 50 kg and let them from a big height. The reason that they will reach at same time will be that the Earth will put different power about their mass so to catch the asseleration of 10m/s^2. Is that right?
 
Physics news on Phys.org
Hey! the answer is "no", that's not right this doesn't have anything to do with power. Everything falls with the same acceleration because this acceleration is independent of the mass, some easy calculations can be done to show it.
 
Remember that power is work per unit of time, such as joules per second, and is expressed in Watts.
And work is force acting over a distance. W=fd.
So you are correct in that the larger object has "more power", as it can perform more work than a less massive object, but we don't usually put it that way as it isn't really correct. Instead, we say that a greater force is applied to the more massive object. This increase in force is exactly counterbalanced by the increase in mass, thus leading to the acceleration being exactly the same between objects of different masses.
 
I think Hepic has got the right idea, only uses non-physical nomenclature.

What he says is that the force(not power) of gravity is proportional to the mass of the falling body, so in the end when we put F=F_g → ma=\frac{GMm}{R^2} the mass m cancels out and we get acceleration independent of it:
a=\frac{GM}{R^2}
 
christianpoved said:
Hey! the answer is "no", that's not right this doesn't have anything to do with power. Everything falls with the same acceleration because this acceleration is independent of the mass, some easy calculations can be done to show it.

Bandersnatch said:
I think Hepic has got the right idea, only uses non-physical nomenclature.

What he says is that the force(not power) of gravity is proportional to the mass of the falling body, so in the end when we put F=F_g → ma=\frac{GMm}{R^2} the mass m cancels out and we get acceleration independent of it:
a=\frac{GM}{R^2}
exactly
why to go to that power where we have this
acceleration same then time to cover same distance is same
 
Drakkith said:
Remember that power is work per unit of time, such as joules per second, and is expressed in Watts.
And work is force acting over a distance. W=fd.
So you are correct in that the larger object has "more power", as it can perform more work than a less massive object, but we don't usually put it that way as it isn't really correct. Instead, we say that a greater force is applied to the more massive object. This increase in force is exactly counterbalanced by the increase in mass, thus leading to the acceleration being exactly the same between objects of different masses.
Is this allways true for different masses of any size.A weight does not fall at the same rate on the Moon as on Earth.
 
A non rigorous way to explain why the 50Kg behaves the same as
a 30 Kg object is the following.
The 50Kg object experiences more FORCE [F = ma = mg],
But it also has more inertia and thus more resistance to a change in its velocity.
The two effects balance to give either object the same acceleration.
 
Note that we have an FAQ about this, in the "Frequently Asked Questions" section at the top of this forum. :smile:

https://www.physicsforums.com/showthread.php?t=511172
 
Last edited by a moderator:
  • Like
Likes   Reactions: 1 person
Thank you.you were clear,but I have a question too.How a planet understands that an object has more mass from an other so put more force?
 
  • #10
hi Hepic

so you really didn't quite understand ? :wink:

did you read the link jtbell pointed you to ?

the Earth doesn't know anything ... It doesn't have a mind, to quote a comment from his link ...


What I'm trying to show here is in this scenario, the Earth does not make any significant motion due to the force exerted by m 1 . This means that for this case, it is perfectly fine to consider the Earth as the fixed object, and only consider that it is the smaller mass that falls towards the earth. So when you consider that, then all the simplification that is done to allow us to deduce that the acceleration due to gravity of ALL objects falling on the surface of the Earth to be a constant, independent of the mass of the object.

Note the bolded section

Dave
 
  • #11
What is not quite so clear is the last part of the link.
However, if we change that situation, i.e. if m 1 is now comparable, or even bigger, than M , then those simplifications will no longer be valid, and one will have to start from the very beginning to figure this out.
Small masses have a small effect on the Earth.Once the masses get quite large they do and the Earth no longer remains a fixed object.This only happens when the object is comparable in size to the Earth.The Moon is quite a bit smaller but comparable in size and would have an effect.
How large an object has to be to be comparable is not so clear.
 

Similar threads

High School The Effect of Linear and Rotational Motion on Measured Weight
  • · Replies 10 ·
Replies
10
Views
929
Undergrad Question about the velocity of the center of mass reference frame
  • · Replies 21 ·
Replies
21
Views
2K
Undergrad Why do objects fall at the same speed in free fall?
  • · Replies 30 ·
2
Replies
30
Views
6K
High School Mobility in a Strong Gravity Environment vs. Moving Mass?
  • · Replies 10 ·
Replies
10
Views
1K
Undergrad Terminal velocity of two balls with different masses
  • · Replies 22 ·
Replies
22
Views
23K
High School What Happens When an Object on Earth Loses Mass Suddenly?
  • · Replies 6 ·
Replies
6
Views
2K
High School Mass of falling objects vs. their acceleration
  • · Replies 7 ·
Replies
7
Views
3K
High School Help Scaling Gravity Simulation
  • · Replies 7 ·
Replies
7
Views
3K
High School Misleading Textbook Equation for vf^2=vi^2 + 2ad
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Conceptual Force of Gravity Acceleration 2 vs 3 objects
  • · Replies 4 ·
Replies
4
Views
1K