Calculating Frictional Force: A Problem-Solving Guide

  • Thread starter Thread starter gracemir
  • Start date Start date
  • Tags Tags
    Friction
Click For Summary
SUMMARY

The discussion focuses on calculating the frictional force acting on a 40-N crate subjected to a 12-N horizontal force, with static and kinetic friction coefficients of 0.5 and 0.4, respectively. Participants clarify that both static and kinetic friction coefficients should not be used simultaneously in calculations. The correct approach involves determining if the applied force is sufficient to overcome static friction before calculating the actual frictional force, which is derived from the net force and the normal force.

PREREQUISITES
  • Understanding of static and kinetic friction coefficients (µs and µk)
  • Knowledge of Newton's laws of motion
  • Ability to calculate normal force in a horizontal system
  • Familiarity with force equilibrium concepts
NEXT STEPS
  • Study the differences between static and kinetic friction in detail
  • Learn how to apply Newton's laws to solve static equilibrium problems
  • Explore examples of frictional force calculations in various scenarios
  • Investigate the effects of different surface materials on friction coefficients
USEFUL FOR

Students studying physics, educators teaching mechanics, and anyone interested in understanding the principles of friction and force calculations.

gracemir
Messages
5
Reaction score
0
A 40-N crate rests on a rough horizontal floor. A 12-N horizonatl force is then applied to it. If the coefficients of friction are s = 0.5 and k = 0.4, the magnitude of the frictional force on the crate is:

what i did was :
40*0.5=20 , 40*0.4=16 20+16=36 40/12=3.3 36/3=12

how to solve this problem? could someone help?
thank you.
 
Physics news on Phys.org
Welcome to PF!

Hi gracemir! Welcome to PF! :smile:

(have a mu: µ :wink:)
gracemir said:
… what i did was :
40*0.5=20 , 40*0.4=16 20+16=36

Nooo … you never use both µs and µk …

it's always either one or the other! :wink:

Hint: first decide whether 12N is enough to move the crate, then decide what the friction force is. :smile:
 


how to decide whether 12N is enough to move or not?

tiny-tim said:
Hi gracemir! Welcome to PF! :smile:

(have a mu: µ :wink:)


Nooo … you never use both µs and µk …

it's always either one or the other! :wink:

Hint: first decide whether 12N is enough to move the crate, then decide what the friction force is. :smile:
 
gracemir said:
how to decide whether 12N is enough to move or not?

oh come on … think …

what is the definition of µs ?​
 
the definition of mu s is F sub s / N?

tiny-tim said:
oh come on … think …

what is the definition of µs ?​
 
gracemir said:
the definition of mu s is F sub s / N?

No.

µs is the maximum possible value of Fs/N.

To find the actual value of Fs, we can use the fact that the acceleration (and velocity) is zero, so all the forces must add to zero. :smile:
 

Similar threads

Relationship between horizontal force and friction in an exercise
  • · Replies 7 ·
Replies
7
Views
1K
Find the Coefficient of Kinetic Friction for Crate Movement
  • · Replies 2 ·
Replies
2
Views
2K
Frictional Force vs normal force
  • · Replies 2 ·
Replies
2
Views
3K
Static and kinetic friction help?
  • · Replies 1 ·
Replies
1
Views
1K
For the friction formula when to use Fn(normal force)×mu and when F×mu
  • · Replies 17 ·
Replies
17
Views
2K
Yes! Calculating Friction Coefficient
  • · Replies 1 ·
Replies
1
Views
1K
Negative Values of the Frictional Force?
  • · Replies 29 ·
Replies
29
Views
6K
Frictional Forces on a Wooden Crate with External Forces
  • · Replies 1 ·
Replies
1
Views
2K
Rolling without slipping problem
  • · Replies 42 ·
2
Replies
42
Views
4K
Calculate the work done moving a crate
  • · Replies 3 ·
Replies
3
Views
3K