Derivation of orbital velocity formula

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Discussion Overview

The discussion revolves around the derivation of the orbital velocity formula, specifically seeking a method to calculate it based on altitude and acceleration without employing calculus. Participants explore various approaches, including the use of gravitational potential and kinetic energy, and debate the necessity of calculus in understanding centripetal acceleration and orbital mechanics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions if a mathematical derivation for orbital velocity can be achieved without calculus, suggesting the use of equations of motion and gravitational principles.
  • Another participant proposes that assuming a circular orbit allows for a derivation without calculus by equating centripetal force to gravitational force.
  • Some participants argue that deriving centripetal acceleration requires calculus, while others assert that it can be shown using basic algebra or geometry.
  • A participant mentions that even basic concepts like instantaneous speed and acceleration are fundamentally tied to calculus, challenging the idea of avoiding it entirely.
  • Discussion includes references to external resources, such as Wikipedia, for derivations and explanations of centripetal force.
  • One participant notes that in a stable orbit, gravitational acceleration equals centripetal acceleration, leading to a specific equation involving gravitational constant and mass.
  • Another participant suggests that using limits instead of derivatives might help in understanding the concepts with minimal calculus.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of calculus for deriving orbital velocity. Some maintain that it is possible to derive the concepts without calculus, while others argue that calculus is inherently involved in the definitions of key terms like acceleration and velocity. The discussion remains unresolved regarding the best approach to derive the orbital velocity formula.

Contextual Notes

Participants highlight the limitations of their approaches, including the dependence on definitions of acceleration and velocity, and the unresolved nature of using algebra or geometry without invoking calculus concepts.

Amr Elsayed
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Is there some mathematical derivation for calculating the orbital velocity based on altitude and acceleration without using calculus? I thought of equations of motion, but I always get problems.
Is there a way to derive it using laws of gravitational potential and kinetic energy ?

Are the pieces of information here in the video correct ? I guess it has mistaken with the position of the satellite if not affected with gravity.
 
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If you assume the orbit is a circle, you can do it without Calculus.

Set the force you need (for centripetal acceleration) equal to the force you have (Newton's law of gravitation).

The orbital radius is the Earth's radius plus the altitude.

Simplify.
 
Dr. Courtney said:
et the force you need (for centripetal acceleration) equal to the force you have (Newton's law of gravitation).
But I need to use : F centripetal = M*V^2 / r .. Which needs calculus to be derived. I want to understand it without calculus if possible
 
Amr Elsayed said:
But I need to use : F centripetal = M*V^2 / r .. Which needs calculus to be derived.

That isn't true. There are a few ways to show that ##a_{centripetal}=\frac{V^2}{R}## without calculus.
 
negligible mass satellite assumed
for stable orbit: gravitational acceleration = centripetal acceleration
so:
( G * M ) / r^2 = v^2 / r
 
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You actually just need very little calculus, but you can instead think of it as the limit approaching to zero rather than the derivative and that should help you.
 
Actually even the notion of instantaneous speed is based on calculus. So if you use instantaneous speed in the formula for acceleration you "use calculus".
Defining it as a limit rather than a derivative is still calculus. The notion of limit is one of the basic notions in calculus. And the derivative itself is such a limit.

So technically, you cannot do kinematics at all without calculus. You may have the illusion that you do without. :)
After all, Newton had to invent it before he can study motion.
 
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  • #10
A handy bit of info:
In a stable orbit two body situation, each body has equal momentum.
Have a look at this two body data sheet also.
 

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Amr Elsayed said:
Can you please show me any of them using basic algebra or geometry ?

Even if you want to use geometry, you will have to use it in a way that allows for calculus (i.e. allow for derivatives) ...otherwise words like "Acceleration" or "velocity" won't make any sense...
As for basic algebra, I don't know what that would mean... like addition, multiplication etc?
 

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