Classical mechanics |
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${\vec {F}}=m{\vec {a}}$ |
Core topics |
Sliding is a type of frictional motion between two surfaces in contact. This can be contrasted to rolling motion. Both types of motion may occur in bearings.
The relative motion or tendency toward such motion between two surfaces is resisted by friction. Friction may damage or 'wear' the surfaces in contact. However, wear can be reduced by lubrication. The science and technology of friction, lubrication, and wear is known as tribology
Sliding may occur between two objects of arbitrary shape, whereas rolling friction is the frictional force associated with the rotational movement of a somewhat disclike or other circular object along a surface. Generally the frictional force of rolling friction is less than that associated with sliding kinetic friction.^{[1]} Typical values for the coefficient of rolling friction are less than that of sliding friction.^{[2]} Correspondingly sliding friction typically produces greater sound and thermal bi-products. One of the most common examples of sliding friction is the movement of braking motor vehicle tires on a roadway, a process which generates considerable heat and sound, and is typically taken into account in assessing the magnitude of roadway noise pollution.^{[3]}
Sliding friction (also called kinetic friction) is a contact force that resists the sliding motion of two objects or an object and a surface. Sliding friction is almost always less than that of static friction; this is why it is easier to move an object once it starts moving rather than to get the object to begin moving from a rest position.
$F_{kF}=\mu _{k}\cdot N$
Where F_{k}, is the force of kinetic friction. μ_{k} is the coefficient of kinetic friction, and N is the normal force.
The motion of sliding friction can be modeled (in simple systems of motion) by Newton's Second Law
$\sum F=ma$
$F_{E}-F_{k}=ma$
Where $F_{E}$ is the external force.
One of the most common physics problems in introductory physics classes is a block subject to friction as it slides up or down an incline plane.
In this case the force of gravity is accounted for and is given by:^{[4]}
$F_{g}=mg\sin {\theta }$
The force of friction opposes the motion of the block and the normal force (perpendicular to the surface is given by:
$N=mg\cos {\theta }$
Therefore:
$F_{k}=\mu _{k}\cdot mg\cos {\theta }$
To find the coefficient of kinetic friction on an incline plane, one must find the moment where the force parallel to the plane is equal to the force perpendicular; this occurs when the block is moving at a constant velocity at some angle $\theta$
$\sum F=ma=0$
$F_{k}=F_{g}$ or $mg\cos {\theta }=\mu _{k}mg\sin {\theta }$
Here it is found that:
$\mu _{k}={\frac {mg\sin {\theta }}{mg\cos {\theta }}}=\tan {\theta }$ where $\theta$ is the angle at which the block begins moving at a constant velocity^{[5]}
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3D,Geneva double,mechanism,kinematics,rotation,translation