Why does the frictional force in case of circular motion point towards the center even though the motion is tangential to the radius?
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$\begingroup$ So why does the friction not point opposite to the rolling of the wheels...friction forces act as a response, and opposite, to velocity right? $\endgroup$– oshhhCommented May 25, 2016 at 12:57
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1$\begingroup$ If the car were to hit an ice patch, it would slide outward. The friction force pointing inward is what allows the car to maintain its circular path. See centripetal force. $\endgroup$– mbeckishCommented May 25, 2016 at 13:16
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2 Answers
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The force of friction acts both towards the centre of the circle and opposite the velocity vector of the car. Strictly speaking, the diagram you have does not show all forces acting on the car but it is enough for purposes of explaining the circular motion.
As the text also explains, circular motion always requires a force pointed radially inwards because the object is changing its velocity. Newton's first law of motion tells us that a change in motion requires a force to act on the object.
A car driving through a curve "wants" to go in a straight path because of its inertia but it actually takes a turn. Because the force that provides the centripetal acceleration opposes the natural tendency of the car to move outwards, it is feasible for this force to be frictional in nature.
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$\begingroup$ How is friction able to act opposite to the car when its actually providing centripetal acceleration $\endgroup$– AbhinavCommented Jul 20, 2018 at 0:46
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$\begingroup$ There are two (more or less) independent orthogonal friction vectors; one caused solely by the linear motion of the car and one caused by its inertial tendency to leave a circular path. So friction doesnt only have to act in one direction if thats what youre confused about $\endgroup$ Commented Jul 20, 2018 at 8:08
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$\begingroup$ So what would this component of friction.....reduce velocity of car ? $\endgroup$– AbhinavCommented Jul 20, 2018 at 9:25
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$\begingroup$ No, change the direction of the velocity. $\endgroup$– KarthikCommented Dec 27, 2018 at 15:47
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1$\begingroup$ @Jaywalker How friction have direction perpendicular to velocity if it always opposes relative motion? $\endgroup$ Commented Sep 4, 2020 at 18:19
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Imagine that friction between wheels and road disappeared in one second. Then the car would just go away moving straight along tangential direction, right? In the life it doesn't, consequently there is centripetal acceleration that keeps the car on the circle way. Consequently there is some force doing that. It is friction.
