Speed, energy, power and air resistance

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Discussion Overview

The discussion revolves around the relationship between speed, energy, power, and air resistance, particularly focusing on how changes in speed affect drag force and energy consumption over a fixed distance. Participants explore the implications of these relationships in both theoretical and practical contexts.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant states that doubling speed results in drag increasing by four times, leading to a requirement for approximately four times more power and energy consumption for a specific time period.
  • Another participant counters that power actually increases by eight times due to the relationship between drag and speed, noting that while drag is four times higher, speed is doubled, resulting in a shorter time to cover the same distance.
  • There is a discussion about the non-intuitive nature of how power increases in relation to drag.
  • Participants mention that aerodynamic drag force is proportional to the square of the speed and that power required is the product of drag force and speed, with a consideration of rolling resistance.
  • One participant raises a question about whether fuel consumption, defined as energy consumed, corresponds to power multiplied by time, and another confirms this while adding the caveat of including engine efficiency.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between speed, power, and energy consumption, particularly regarding the calculations of power requirements and the implications of drag force. There is no consensus on the correct interpretation of these relationships.

Contextual Notes

Participants note the importance of considering engine efficiency when discussing power and fuel consumption, indicating that assumptions about efficiency may affect the conclusions drawn from the discussion.

Patrick Pihl
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What is wrong here. If I double speed drag will be 4 times higher. The engine needs to put out approximately 4 times more power. Energy consumption will be 4 time higher for a specific time period. However if it is a fixed distance I will arrive in half the time an the energy consumption will therefore only double. Now if I look on the formula E=FxS (energy=Force x Distance) the force will be 4 times higher and therefore also the total energy needed. //Thanks
 
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Patrick Pihl said:
What is wrong here. If I double speed draft will be 4 times higher. The engine needs to put out approximately 4 times more power. Energy consumption will be 4 time higher for a specific time period.
No, power (energy over a specific time) is 8x higher. Drag is 4x higher, and speed is 2x higher (or time is 1/2 as long).
 
russ_watters said:
No, power (energy over a specific time) is 8x higher. Drag is 4x higher, and speed is 2x higher (or time is 1/2 as long).

Well, then it make sense. Not very intuitive (to me) that power increase that way in relation to drag.
 
the aerodynamic drag force is proportional to the square of the speed
power required is : ( aerodynamic drag force overcome (+ rolling resistance if you want) ) * speed

if fuel consumption is energy consumed, is this power * time ?
 
dean barry said:
the aerodynamic drag force is proportional to the square of the speed
power required is : ( aerodynamic drag force overcome (+ rolling resistance if you want) ) * speed

if fuel consumption is energy consumed, is this power * time ?
That's correct...if you also include engine efficiency.
 

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