anonymous
  • anonymous
At what direction is the frictional force?
Physics
  • Stacey Warren - Expert brainly.com
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jamiebookeater
  • jamiebookeater
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anonymous
  • anonymous
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BTaylor
  • BTaylor
The frictional force is parallel to the surface, opposing the motion. So, it would be pointing down the slope, if the drawing in the arrow represents the motion.
anonymous
  • anonymous
Yes, the arrow represent the motion. But ummm, i'm not sure the frictional force is parallel to the surface, opposing the motion. Just like when we walk, the frictional force is in the same direction as our motion....

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BTaylor
  • BTaylor
No, it's not. The friction always opposes motion.
anonymous
  • anonymous
|dw:1348327921150:dw|
anonymous
  • anonymous
|dw:1348328024524:dw|
BTaylor
  • BTaylor
the friction force reduces the acceleration of the object. When you are walking, the friction between your shoe/foot and the ground keeps your foot from sliding forward indefinitely.
anonymous
  • anonymous
|dw:1348328081329:dw|
anonymous
  • anonymous
@BTaylor yes, it oppose the motion, but the motion of our shoes.
anonymous
  • anonymous
the a point is moving in rotation direction so frictions force oppose it
anonymous
  • anonymous
that's why the car can rise rump
anonymous
  • anonymous
get @imron07 ?
anonymous
  • anonymous
@RaphaelFilgueiras : What about this:
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anonymous
  • anonymous
im talking about this
anonymous
  • anonymous
|dw:1348328369452:dw|
anonymous
  • anonymous
|dw:1348328561760:dw|
anonymous
  • anonymous
the friction is opposite to the moviment of weel
anonymous
  • anonymous
|dw:1348328592225:dw|
anonymous
  • anonymous
Yeah, i understand your explanation. But if we apply Newton's law, should we pick that direction too for friction to find system acceleration?
anonymous
  • anonymous
the friction is opposite to the moviment of POINT OF CONTACT
anonymous
  • anonymous
yep
anonymous
  • anonymous
Yes ma = mgsin alpha + f
anonymous
  • anonymous
f-mgsin(alpa)=ma
anonymous
  • anonymous
Shouldn't \(mg\sin{\alpha}\) is in opposite direction with friction now?
anonymous
  • anonymous
yes it is opposite
anonymous
  • anonymous
@RaphaelFilgueiras yes that's what I mean :)
anonymous
  • anonymous
NO it is coincident with mg sin alpha : here is why (let me finish pls
anonymous
  • anonymous
T|dw:1348328885247:dw|
anonymous
  • anonymous
And when wheel is freely rolling the friction acts BACK on it
anonymous
  • anonymous
so your car never will rise the ramp!!!
anonymous
  • anonymous
@RaphaelFilgueiras you are wrong : in his picture there are NO OTHER forces. The cart is only rolling up BY INERTIA and of course slows eventually. This is different from motorized climbing up !!!
anonymous
  • anonymous
the car is moving up
anonymous
  • anonymous
The point of contact is moving a wee-bit slower than the surface - so the surface ACCELERATES it !
anonymous
  • anonymous
@Mikael : So only when the engine turned on, friction will directed upward?
anonymous
  • anonymous
YES @imron07
anonymous
  • anonymous
And pls medal (-s)
anonymous
  • anonymous
the vector is velocity. And please admit that I am right @RaphaelFilgueiras
anonymous
  • anonymous
Again I clarify : When the wheel is free it serves as a friction-conduit from the surface to cart. When the motor is working the opposite: the wheel transfers torque from cart to surface
anonymous
  • anonymous
It is a delicate but DRAMATIC CHANGE
anonymous
  • anonymous
Well, i understand both of your opinion. But i agree with @Mikael . If the vector I draw is Force, would something change (engine on)?
anonymous
  • anonymous
Of course - all is opposite
anonymous
  • anonymous
they are opposite but mg is greater than f
anonymous
  • anonymous
so it will stop,and then the friction and mg will be in same direction
anonymous
  • anonymous
This time @RaphaelFilgueiras IS ok. Though he will never admit someone else IS .....
anonymous
  • anonymous
The last remark of Raf is WRONG (again!)_
anonymous
  • anonymous
You mean friction is downward even if the tire's working to move the car upward too?
anonymous
  • anonymous
Friction is UPWARD when the tire PUSHES the surface (working) and downward when the SURFACE pushes the tire
anonymous
  • anonymous
Both of you should imagine a tiny (really tiny) velocity difference betwee Contact point and surface. It has OPPOSITE directions in these opposite cases !
anonymous
  • anonymous
@Mikael can you draw it please, (when engine turned on, and another force pull the car too).
anonymous
  • anonymous
When wheel PUSHES it is faster downward - so frict is UPWARD
anonymous
  • anonymous
|dw:1348329423502:dw|
anonymous
  • anonymous
|dw:1348329805336:dw|
anonymous
  • anonymous
Okay, I understand now. Thanks @RaphaelFilgueiras & @Mikael !
anonymous
  • anonymous
yw
anonymous
  • anonymous
You see the friction force is OPPOSITE to the RELATIVE VELOCITY\[V_{contact} - V_{\text{surface velocity relative \to wheel's center}}\]
anonymous
  • anonymous
Yeah, that's what in my mind :D
anonymous
  • anonymous
@imron07 and @RaphaelFilgueiras : Thank you both for educating me and all of us by your questions and thoughts.
anonymous
  • anonymous
It was a nice discussion :)
anonymous
  • anonymous
DUBITANDO AD VERITATEM PERVENIMUS !
anonymous
  • anonymous
Veritas in disputando gignitur.
anonymous
  • anonymous
What's that last phrase means?
anonymous
  • anonymous
http://translate.google.com/#la/en/Veritas%20in%20disputando%20gignitur.
anonymous
  • anonymous
http://translate.google.com/#la/en/PERVENIMUS%20DUBITANDO%20AD%20VERITATEM
anonymous
  • anonymous
|dw:1348331561351:dw|
anonymous
  • anonymous
@experimentX
anonymous
  • anonymous
@RaphaelFilgueiras : can you explain more about your pic please?
anonymous
  • anonymous
forget the plane|dw:1348332081044:dw|
anonymous
  • anonymous
Okay, agree, then
anonymous
  • anonymous
|dw:1348332372621:dw|
anonymous
  • anonymous
the direction of friction is always in the moviment direction
anonymous
  • anonymous
in this case
anonymous
  • anonymous
Yes, please continue
anonymous
  • anonymous
so in your picture f is in direction of moviment
anonymous
  • anonymous
You mean my first, or second picture (or both)?
anonymous
  • anonymous
get it?
anonymous
  • anonymous
just matter the direction of moviment
anonymous
  • anonymous
Mmm, still thinking. For the first picture, it makes sense. But for the seecond (where another force pull the car)?
anonymous
  • anonymous
no matter the friction is always in direction of moviment
anonymous
  • anonymous
What disturb me: when we calculate the car's acceleration, ma=F+f-mg*sin(theta) It seems friction 'helps' F to push the car up.
anonymous
  • anonymous
the second car is moving?
anonymous
  • anonymous
but friction help,imagine if there is no friction a car will not move when you accelarate it,the wheel will slip
anonymous
  • anonymous
The force of friction is the only force that actually pushes a motor-vehicle that produces work. Yes it "helps" motion of vehicle by OPPOSING the backward motion OF THE WHEEL CONTACT POINT. For visual clarity - look at this wheeled vehicle . What pushes it forward on land or in water ? Well the friction force of course - friction of wheel contact point with the surface !
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anonymous
  • anonymous
@imron07 read.
anonymous
  • anonymous
by the way I have a more measurement oriented proof for you. You can measure the DIRECTION of friction force with your hands and feet DIRECTLY. Experiment 1: CLIMB A CHILDRENS Kindergarten's slide with your palms. What do you feel - does the friction help you climb ? Well of course ! But now Experiment 2: Slide on your derriere DOWN the slide. Does the friction obstruct your motion ? or Better - try rolling a small coin on flat plane. Frictions opposes of course. See I gave the correct description
anonymous
  • anonymous
@imron07
anonymous
  • anonymous
@TuringTest @myininaya
anonymous
  • anonymous
kinetic Frictional force always opposes the moving body... therefore its always is in the opposite direction :B http://wiki.answers.com/Q/What_is_the_direction_of_the_frictional_force_on_a_moving_object|dw:1348390006451:dw|
anonymous
  • anonymous
@Alice_Dump : Thanks for contribution, but I think you should read all the comments from beginning :D #Nice drawing btw ;)
anonymous
  • anonymous
:B whatevaa
anonymous
  • anonymous
She is quite pretty (on the pic at least) - so @imron07 don't you know the law of excluded THIRD ? Given a human fem. the maximal number of included properties is 2, from the following set Beauty, Goodness, Smarts
anonymous
  • anonymous
>_ >
AravindG
  • AravindG
@imrom07 Fricion does not always oppose motion !!!! it only opposes the relative sliding between surfaces , indeed its due to friction we can walk, travel in vehicle and al!!

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