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## Class 11 Physics (India)

### Course: Class 11 Physics (India)>Unit 9

Lesson 9: Friction

# Force of friction keeping the block stationary

Block of wood kept stationary by the force of friction (Correction made in next video). Created by Sal Khan.

## Want to join the conversation?

• Can friction support the direction of motion? If so, how??
• Friction does not support in the direction of motion but helps motion. When we push the ground with our feet its due to friction that our shoes don't slip away and help us to move forward. So, friction helps in motions but does not act in the direction of motion.
• What is this "budging force" actually called?
• It’s called the static coefficient of friction.
(1 vote)
• Is the 'budging force' that Sal refers to greater than the maximum force of static friction?
• I would say yes. The "budging force" gets the block moving again, so it must be greater than the friction keeping the block stationary.
• Is it possible for friction to be more then 49N. For example the ramp can hold the wood block but also can hold a heavier car. If yes, does a ramp have a certain amount of total friction and only uses a little for smaller objects and more for bigger objects until you have an object with an Fg parallel which exceeds the capacity of the max amount of friction where it can slide down
• The amount of friction depends on many factors

Well i am answering it 6 years later
i don't think it will do anything
• When you are calculating the static friction coefficient, would the operation be 50N/49(3)^1/2? or 50N/40(3)^1/2? I could be wrong, but I think this is a mistake and the static coefficient (Ms) should be 0.589 found by performing the operation: 50N/49(3)^1/2.
• How can you say, that 49N is the maximum friction force? Maybe it is 51N or 60N, and then your 50N parallel force wouldn't be enough?
• If you know the coefficient of static friction and the normal force between the object and the surface the product of these two numbers by definition is the maximum force of static friction. So if you calculate the force to be 49N and 50N doesn't move the object then either the value for the coefficient of static friction or the normal force are wrong.
• Is the coefficient of friction always depends on the identity of the matirials involved? Or is there a general rule for it?
• Sal does this:
Coefficient of static friction= 50/N
Coefficiente of cinetic friction= 49/N
So if I want in an exercise discover the force of friction when the object is stationary shall I do: Force of friction= Coefficiente of static friction * N - 1 ??

following Sal's logic.... Help please :\
(1 vote)
• The kinetic coefficient of friction is not always the same amount less than static friction, in some cases it could even be more, because friction relies on many factors.
• What would the F(net) be in this?
(1 vote)
• There are 3 forces---Gravity Supporting force Friction Use the sin/cos to calculate