What does it mean by 'a is constant' in motion..........'?

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    Constant Mean Motion
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Discussion Overview

The discussion revolves around the concept of constant acceleration in motion, specifically what it means for acceleration (denoted as 'a') to be constant in the context of motion equations. Participants explore the implications of this condition in various scenarios, including real-world applications and limitations.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants assert that constant acceleration means the acceleration does not change over time.
  • One participant notes that constant acceleration is typically observed in scenarios like free fall, where air resistance is negligible.
  • Another participant highlights that real-world situations, such as cars and rockets, often do not exhibit constant acceleration due to varying factors like mass and external forces.
  • A participant expresses confusion about the application of constant acceleration formulas in practical contexts, indicating a need for clarification.
  • Some participants emphasize that while the formulas are useful, they are simplifications that do not accurately represent most real-world motion.

Areas of Agreement / Disagreement

Participants generally agree on the definition of constant acceleration but express differing views on its applicability in real-world scenarios, indicating that multiple competing perspectives remain regarding the relevance of the concept.

Contextual Notes

Limitations include the assumption that acceleration is constant, which may not hold true in many practical situations. The discussion acknowledges that real-world factors can complicate the application of the motion equations.

HCverma
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Motion in a straight line has three formulas
1. v = u + at
2. v^2 - u^2 = 2as
3. s = ut + 1/2 at^2
These three formulas are applicable when a is constant. Now my question is 'what does it mean by 'when a is constant'? Could you please explain it?
 
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It means the acceleration is constant over time.
 
HCverma said:
Now my question is 'what does it mean by 'when a is constant'?
About the only 'constant acceleration' situation we encounter is when an object falls from a height of a few tens of metres and when it has a big enough mass that we ignore the effect of air resistance. I must have had my attention elsewhere when those formulae were first presented to me and I spent a lot of time worrying about how that could possibly apply to motor cars accelerating ("Pay attention you little oik!"). It was much later that I actually cottoned on properly.
Cars of course do not accelerate at a constant rate and neither do space rockets because they lose fuel constantly so their mass reduces throughout the burn. But we all need to learn to use those formulae because we have to start somewhere.
 
HCverma said:
Now my question is 'what does it mean by 'when a is constant'? Could you please explain it?

It means that the acceleration always has a single value and does not vary. The real world almost never follows this simplification though.
 
sophiecentaur said:
Cars of course do not accelerate at a constant rate and neither do space rockets because they lose fuel constantly so their mass reduces throughout the burn.
Or the classic example of an object that often undergoes non-constant acceleration... :biggrin:

https://c8.alamy.com/comp/E5P2E2/a-...h-fighter-aircraft-performs-aerial-E5P2E2.jpg

a-us-air-force-f-22-raptor-stealth-fighter-aircraft-performs-aerial-E5P2E2.jpg
 

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