Can anyone help provide an explanation?

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Homework Help Overview

The discussion revolves around understanding the dynamics of motion in fluids, specifically in the context of paddling a canoe and the flight of jet planes. The original poster poses questions about the relationship between speed, effort, and drag forces in these scenarios.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the concepts of drag force and friction in relation to speed in both canoeing and aviation. Questions arise regarding the effects of altitude on air density and drag, as well as the implications for lift and fuel efficiency.

Discussion Status

The discussion is active, with participants sharing insights about the principles of drag and air density. Some guidance has been offered regarding the relationship between speed and drag force, particularly in the context of the canoe question, though explicit consensus has not been reached.

Contextual Notes

Participants are navigating assumptions about fluid dynamics and the effects of altitude on flight, with a focus on the implications for both drag and lift. The original poster expresses uncertainty about the canoe scenario, indicating a need for further exploration of the topic.

gunblaze
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Qn1: When paddling a canoe, one can attain critical speed with relatively little effort, but to go faster beyond this critical speed requires more effort. Why?

Qn2: Why do jet planes usually fly at altitudes above 10000m although it takes a lot of fuel to climb to that height?

Thx..
 
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What are your thoughts?

Hint: Friction
 
yup.. around there. Friction and the drag force
 
but how..? when u fly higher, u get lesser friction..?
 
Right. I may have the number wrong but when flying at the altitudes planes do on long flights (around 30,000 feet) the air is about 20% as thick as it is at sea level.
 
u mean air is less dense at high altitudes, therefore, by using F=pAv^2, we get a lesser drag force?
 
Yeah, the air density is much less up there. This also affects the plane's lift though.

Can you think of anything for the canoe?
 
no.. that's really what i don't know
 
Look at the force equation you gave above for drag resistance. Although that is the application for air, it is a simliar principle for fluids. What do you notice as velocity increases?
 
  • #10
oOO.. I see. so as the speed of the canoe increases, the larger the drag force is on the canoe.

Whao, thanks guys!
 

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