Acceleration Due to Gravity: Facts & Qs

  • Context: High School 
  • Thread starter Thread starter Caesar_Rahil
  • Start date Start date
  • Tags Tags
    Accelerating Gravity
Click For Summary

Discussion Overview

The discussion revolves around the concept of acceleration due to gravity, questioning its validity and implications. Participants explore philosophical and theoretical aspects, including references to Newtonian and relativistic frameworks, while also addressing related hypothetical scenarios.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants question the phrasing of the question regarding the truth of acceleration due to gravity, suggesting it is not well-posed.
  • One participant asserts that the acceleration due to gravity on Earth is defined as 9.8 m/s², implying a factual basis for the claim.
  • Several participants propose a thought experiment involving stepping off a roof to illustrate concepts of acceleration and freefall, with references to Newton's and Einstein's theories.
  • A participant discusses the distinction between inertial and non-inertial frames in the context of general relativity, noting that freefall represents traveling along a spacetime geodesic with zero 4-acceleration.
  • Another participant raises a hypothetical scenario involving an object traveling at 99.99% the speed of light entering a strong gravitational field, questioning whether it could exceed the speed of light.
  • A response to the hypothetical scenario uses the relativistic velocity addition formula to explain why an object cannot exceed the speed of light, even under strong gravitational influence.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the question regarding acceleration due to gravity, with some asserting its truth while others challenge the clarity of the question. The discussion includes competing perspectives on the implications of gravity in relativistic contexts, indicating that no consensus exists.

Contextual Notes

Some participants note the difficulty in addressing the original question due to its ambiguity. The discussion also highlights the complexity of gravitational effects at relativistic speeds, suggesting that assumptions about gravity and acceleration may vary based on the theoretical framework applied.

Caesar_Rahil
Messages
69
Reaction score
0
Is acceleration due to Gravity true?
I know it is a simple question, but I have other questions based on this.
 
Physics news on Phys.org
Caesar_Rahil said:
Is acceleration due to Gravity true?

No.

(I have to make my message longer than 10 characters).
 
I would suggest to both of you that you climb onto the roof of your house (if you live in a high-rise apartment building so much the better!), step off the roof and see whether or not you are accelerated!
 
There is a reason why we say the acceleration due to gravity on Earth is 9.8m/s^2

Unless I am completely missing the point...
 
HallsofIvy said:
I would suggest to both of you that you climb onto the roof of your house (if you live in a high-rise apartment building so much the better!), step off the roof and see whether or not you are accelerated!
Would this be a test of Newton's theory, Darwin's, or both?
 
Is philosophy real? :-)
 
Caesar_Rahil said:
Is acceleration due to Gravity true?
This is not a well-posed question.
HallsofIvy said:
I would suggest to both of you that you climb onto the roof of your house (if you live in a high-rise apartment building so much the better!), step off the roof and see whether or not you are accelerated!
In the spirit of this SR/GR forum... According to GR...
  • after you step off your roof, you are traveling inertially... that is, you are in freefall, traveling along a spacetime geodesic... your 4-acceleration is zero.
  • when you stand on your roof [or after you hit the ground], you are not traveling inertially, not traveling along a spacetime geodesic, and have a non-zero 4-acceleration.
 
pervect said:
Is philosophy real? :-)
O-Man! Come on! I can't answer that! I'm still trying to figure out if I'm real. :smile:

Pete
 
HallsofIvy said:
I would suggest to both of you that you climb onto the roof of your house (if you live in a high-rise apartment building so much the better!), step off the roof and see whether or not you are accelerated!

I would suggest that you do that too, but carry drop several items alongside you. Notice that you and all the objects move alongside each other, regardless of rest mass and see that there is no acceleration, as robphy has pointed out.
 
  • #10
Now that we have determined that there is acceleration due to gravity, what other questions do you have that you say are based on this fact?
 
  • #11
Caesar_Rahil said:
Is acceleration due to Gravity true?
I know it is a simple question, but I have other questions based on this.
It's far too difficult to respond to this question as stated since its unclear as to what is being asked.

I do, however, recommend that you avoid doing HallsofIvy's experiment. :smile:

I can't say more than robphy has already. He's a sharp man and beat me to what I'd have said. :approve:

Caesar - Can you refine your question more please? Thanks.

Pete
 
  • #12
I never mentioned I have quesions that have to be asked in this forum only.


If a body is traveling with a speed of 99.99% the speed of light(Now don't tell me that's impossible). if it enter a strong gravitation force, say, the sun's wouldn't it be accelerated to a speed faster than light.
 
  • #13
Caesar_Rahil said:
I never mentioned I have quesions that have to be asked in this forum only.
If a body is traveling with a speed of 99.99% the speed of light(Now don't tell me that's impossible). if it enter a strong gravitation force, say, the sun's wouldn't it be accelerated to a speed faster than light.

No, it won't. A simpler problem may illustrate why.

Suppose you have three rockets

A stands still
B moves at .9999c relative to A
---->
C moves at .9999c relative to B
---------->

What is the speed of C relative to A? The answer is given by the relativistic velocity addition formula

(.9999+.9999)/(1+.9999*.9999) = .999999995 times the speed of light.

You can imagine that rocket C is being accelerated either by gravity or a rocket engine (except that it will be hard to find a grav field strong enough to accelerate a rocket to .9999c).

Gravity makes things slightly harder to compute, but the basic principle is the same.
 

Similar threads

High School Gravitational Force acting on a massless body
  • · Replies 67 ·
3
Replies
67
Views
6K
High School Speed of light and this Accelerating Rocket scenario
  • · Replies 45 ·
2
Replies
45
Views
5K
High School Gravity and speed of information for orbiting planets
  • · Replies 22 ·
Replies
22
Views
1K
High School Is Gravity an illusion of a force but really a curvature of spacetime?
  • · Replies 26 ·
Replies
26
Views
2K
Undergrad Gravity: Force or Acceleration?
  • · Replies 69 ·
3
Replies
69
Views
8K
Undergrad Reconciling smooth spacetime with variable, rotating, earth gravity
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Question about Einstein's famous elevator experiment
  • · Replies 29 ·
Replies
29
Views
3K
High School Gravity -- a force or a cause of a force?
  • · Replies 16 ·
Replies
16
Views
4K
High School Where does the energy of gravity come from?
  • · Replies 73 ·
3
Replies
73
Views
7K
High School Gravitational acceleration and sub-atomic electric charge
  • · Replies 12 ·
Replies
12
Views
2K