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BTaylor
 2 years ago
Best ResponseYou've already chosen the best response.0The 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.

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Yes, 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....

BTaylor
 2 years ago
Best ResponseYou've already chosen the best response.0No, it's not. The friction always opposes motion.

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348327921150:dw

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348328024524:dw

BTaylor
 2 years ago
Best ResponseYou've already chosen the best response.0the 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.

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348328081329:dw

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@BTaylor yes, it oppose the motion, but the motion of our shoes.

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1the a point is moving in rotation direction so frictions force oppose it

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1that's why the car can rise rump

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1get @imron07 ?

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@RaphaelFilgueiras : What about this:

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1im talking about this

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348328369452:dw

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348328561760:dw

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1the friction is opposite to the moviment of weel

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Yeah, i understand your explanation. But if we apply Newton's law, should we pick that direction too for friction to find system acceleration?

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1the friction is opposite to the moviment of POINT OF CONTACT

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Yes ma = mgsin alpha + f

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1fmgsin(alpa)=ma

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Shouldn't \(mg\sin{\alpha}\) is in opposite direction with friction now?

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1yes it is opposite

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@RaphaelFilgueiras yes that's what I mean :)

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1NO it is coincident with mg sin alpha : here is why (let me finish pls

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1And when wheel is freely rolling the friction acts BACK on it

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1so your car never will rise the ramp!!!

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1@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 !!!

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1the car is moving up

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1The point of contact is moving a weebit slower than the surface  so the surface ACCELERATES it !

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@Mikael : So only when the engine turned on, friction will directed upward?

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1the vector is velocity. And please admit that I am right @RaphaelFilgueiras

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Again I clarify : When the wheel is free it serves as a frictionconduit from the surface to cart. When the motor is working the opposite: the wheel transfers torque from cart to surface

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1It is a delicate but DRAMATIC CHANGE

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Well, i understand both of your opinion. But i agree with @Mikael . If the vector I draw is Force, would something change (engine on)?

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Of course  all is opposite

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1they are opposite but mg is greater than f

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1so it will stop,and then the friction and mg will be in same direction

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1This time @RaphaelFilgueiras IS ok. Though he will never admit someone else IS .....

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1The last remark of Raf is WRONG (again!)_

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1You mean friction is downward even if the tire's working to move the car upward too?

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Friction is UPWARD when the tire PUSHES the surface (working) and downward when the SURFACE pushes the tire

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Both of you should imagine a tiny (really tiny) velocity difference betwee Contact point and surface. It has OPPOSITE directions in these opposite cases !

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@Mikael can you draw it please, (when engine turned on, and another force pull the car too).

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1When wheel PUSHES it is faster downward  so frict is UPWARD

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348329423502:dw

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Okay, I understand now. Thanks @RaphaelFilgueiras & @Mikael !

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1You see the friction force is OPPOSITE to the RELATIVE VELOCITY\[V_{contact}  V_{\text{surface velocity relative \to wheel's center}}\]

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1Yeah, that's what in my mind :D

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1@imron07 and @RaphaelFilgueiras : Thank you both for educating me and all of us by your questions and thoughts.

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1It was a nice discussion :)

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1DUBITANDO AD VERITATEM PERVENIMUS !

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1Veritas in disputando gignitur.

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1What's that last phrase means?

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1http://translate.google.com/#la/en/Veritas%20in%20disputando%20gignitur.

Mikael
 2 years ago
Best ResponseYou've already chosen the best response.1http://translate.google.com/#la/en/PERVENIMUS%20DUBITANDO%20AD%20VERITATEM

RaphaelFilgueiras
 2 years ago
Best ResponseYou've already chosen the best response.1dw:1348331561351:dw

imron07
 2 years ago
Best ResponseYou've already chosen the best response.1@RaphaelFilgueiras : can you explain more about your pic please?