Question about friction? Dynamics

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Homework Help Overview

The discussion revolves around a dynamics problem involving friction on a ramp, specifically addressing the direction of the frictional force acting on a car. Participants are examining the conditions under which friction acts down the ramp versus up the ramp.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the direction of the frictional force, with some suggesting it should oppose the motion of the car down the ramp. Others explore scenarios involving a flat surface and curves to understand friction's role in different contexts.

Discussion Status

The discussion is active, with multiple participants raising similar questions about the direction of friction. Some have provided insights into the conditions under which friction acts in different scenarios, contributing to a deeper exploration of the topic.

Contextual Notes

Participants are considering the implications of speed on the direction of friction and the specific requirements of the problem, such as determining minimum and maximum speeds for the car on the ramp.

Ricardeo Xavier
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Homework Statement


This is the problem
http://imgur.com/a/1XFlt
rp7otFI.png

2. Homework Equations

This is the given FBD
http://imgur.com/a/CURqA
KpA1w1u.png

3. The Attempt at a Solution

Now the car should have a tendency to slip down the ramp thus causing the frictional force to oppose this motion. But the frictional force is pointed down the ramp in this worked out problem. Can someone explain to me why this is?
 
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Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?
 
If there were no ramp (i.e. the ground was flat) and the car was going around a curve, what direction would the friction force have to point?
 
Ricardeo Xavier said:
Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?
Note that they ask for minimum and maximum speeds. What happens when you take the curve too fast? Which direction do you tend to slip?
 
Ricardeo Xavier said:
Why is friction pointed down the ramp? Shouldnt it be pointed up the ramp?
Follow the sequence of the questions asked by the problem.
First draw the FBD to determine how fast the car must be moving if there were no friction, i.e. sliding around a frictionless curve.
If the car is moving faster than that, friction down the incline is needed to keep it in a horizontal circle.
If the car is moving slower than that, friction up the incline is needed to keep it in a horizontal circle.
 
Thanks everyone for the great responses! It really helped clarify things for me (:
 

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