Mechanics Flashcards
Tangential forces generated between contacting surfaces and occur to some degree in the interaction between all real surfaces
friction forces
A machine or process in which friction is small enough to be neglected is said to be
Ideal
When friction must be taken into account, the machine or process is termed
Real
Types of friction
Dry
Fluid
Internal
occurs when the unlubricated surfaces of two solids are in contact under a condition of sliding or a tendency to slide. Also called coulomb friction
Dry friction
occurs when adjacent layers in a fluid (liquid or gas) are moving at different velocities.
Fluid friction
occurs in all solid materials which are subjected to cyclical loading
Internal friction
The region up to the point of slippage or impending motion is called
range of static friction
is usually somewhat less than the maximum static friction force
Kinetic friction
This opposing force, which acts in the opposite direction of the movement of the block
Force of friction or friction
Two types of friction
Static, dynamic
It is the friction experienced by a body when it is at rest. Or in other words, it is the friction when the body tends to move.
Static friction
It is the friction experienced by a body when it is in motion. It is also called kinetic friction.
Dynamic friction
Two types of dynamic friction
Sliding, rolling
It is the friction, experienced by a body when it rolls over another body
Rolling friction
It is the friction, experienced by a body when it slides over another body
Sliding friction
is the ratio of limiting friction to the normal reaction, between the two bodies, and is generally denoted by μ.
coefficient of friction
laws of static friction
- The force of friction always acts in a direction, opposite to that in which the body tends to move, if the force of friction would have been absent.
- The magnitude of the force of friction is exactly equal to the force, which tends to move the body.
- The magnitude of the limiting friction bears a constant ratio to the normal reaction between the two surfaces.
- The force of friction is independent of the area of contact between the two surfaces.
- The force of friction depends upon the roughness of the surfaces.
laws of kinetic or dynamic friction
- The force of friction always acts in a direction, opposite to that in which the body is moving.
- The magnitude of kinetic friction bears a constant ratio to the normal reaction between the two surfaces. But this ratio is slightly less than that in case of limiting friction.
- For moderate speeds, the force of friction remains constant. But it decreases slightly with the increase of speed.
The term that means that the cables are incapable of developing internal forces other than tension.
flexible
the force of friction has a remarkable property of adjusting its ___, explain
magnitude, so as to become exactly equal and opposite to the applied force, which tends to produce motion.
coefficient of friction
µ = F/N= tan φ
or
F=µN
φ - angle of friction
F - limiting friction
N - normal force
P1, minimum force
= W × (sin (α - φ))/cos φ
P2, maximum force
= W × (sin (α + φ))/cos φ
which is used in suspension bridges, transmission lines, messenger cables for supporting heavy trolley or telephone lines, and many other applications.
flexible cable
The term means that the cables are incapable of developing internal forces other than tension.
flexible
Formula for Tmax ( parabolic cable)
T= sqrt ( To^2 + (wox)^2)
formula for slope angle
tan θ = W/To
a homogeneous cable that carries no load except its own weight
catenary cable
Formula for Tmax (catenary cable)
T= sqrt ( To^2 + (wos)^2)
s as a function of x & To
s(x) = To/wo [sinh ( wox/To)]
Tmax as a function of x & To
Tmax= To [cosh(wox / To)]
determining sag in a catenary cable
y=To/wo [cosh (wox/To) - 1]
