الاحتكاك Friction

Admin عدد المساهمات : 22 تاريخ التسجيل : 02/02/2010

Friction: a force that opposes motion

قوة الاحتكاك تكون فى اتحاة معاكس لاتجاه الحركة

Depends texture of each surface
Forces holding the objects together (example: gravity and weight)

Types of friction أنواع الاحتكاك

Rolling friction أحتكاك الدحرجة : on wheels - riding a bike or skateboard

Rolling friction has less resistive force than sliding friction

When
the Great Pyramids were being build in ancient Egypt, they used logs as
rollers under the giant blocks of granite instead of trying to slide the
rocks along the ground.

Causes of rolling friction

Molecular attraction or adhesion between the materials
Surface roughness of the materials
Deformation resistance in the case of soft materials.

Sliding Friction احتكاك انزلاقى : one surface rubbing against another surface: cartilage against your bone, box against the floor

Two solid objects are in contact
A force is applied to slide one object against the other
Sliding friction force resists the motion

Pushing force greater than friction force

Static Frictionالاحتكاك الساكن :
Pushing force is equal to the resisting force, then there will be no
motion and the objects remain static or still when compared to each
other

once you start an object moving, the friction decreases from the static friction holding the object in place.
You
have seen this in trying to slide a heavy box across the floor. It may
be very difficult to move, but once it starts sliding, it is easier to
push.

Fluid Friction:

When
a solid object is in contact with a fluid, such as a liquid or gas, and
a force is applied to either the object or to the fluid, there is a
friction force that resists the motion
water flowing through a hose, an airplane flying through the atmosphere

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