How is lift force proportional to speed up?

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Discussion Overview

The discussion revolves around the relationship between lift force and upward speed, exploring how lift can influence vertical motion. Participants inquire about calculations related to speed and the forces acting on an object in vertical motion, including weight and thrust considerations.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant expresses uncertainty about calculating the upward speed of an object given a greater lift force.
  • Another participant suggests calculating the net force acting on the object by subtracting weight from lift and applying Newton's second law, indicating that if lift equals weight, the object's vertical velocity remains constant.
  • A question is raised about the definition of weight, specifically whether it refers to atmospheric pressure or the object's mass.
  • A further contribution clarifies that lift acts perpendicular to the direction of travel and discusses the conditions required for a plane to maintain a steady vertical climb, involving thrust and lift components balancing the weight of the aircraft.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the calculation of upward speed, and there are differing interpretations of the concepts of lift and weight. The discussion remains unresolved regarding the specifics of calculating speed in relation to lift force.

Contextual Notes

Limitations include potential misunderstandings of the definitions of weight and lift, as well as the assumptions involved in applying Newton's laws to this context.

thebluser
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i know that if i have a greater lift force, there will be a greater speed upwards, but i don't know to calculate a speed of something upwards. is this even possible to calculate? if it's not, can you give a calculation example??
 
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Work out the net force acting on the object in the vertical direction..

Net Force = Lift - Weight

Then apply Newton..

Net Force = mass * acceleration

If lift = weight then there is no net force acting on the object so it's vertical velocity will be constant (eg acceleration = 0).
 
is weight the atmospheric pressure or how much the body weighs? just want to make sure.
 
By definition, lift is perpendicular to the direction of travel (with respect to the air), so it only changes direction, not speed. If a plane is in a steady vertical climb at some constant angle θ above horitzontal, with a vertical speed component of speed x sin(θ), then there needs to be enough thrust and lift so that the vertical components of thrust and lift equal the weight of the aircraft:

thrust x sin(θ) + lift x cos(θ) = weight.
 
okay then, thank you all!
 

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