Physics - Force

Force

The force which opposes the relative motion between two bodies in contact is called friction.

Friction is of two types:

Static: Force of friction which is introduced when there is no relative motion is called a static friction.it is max when the applied force on its body is such that the body is about to slide. Max friction is called limited friction.

Kinetic Friction: It acts when body slides over the surface.

Some important point about friction:

• Kinetic friction is less than limited friction.
• Its depend upon nature of rough surface.
• it is independent of macroscopic area.
• Friction is proportional to normal reaction.

Rolling Friction: A body rolls over the surface of other body.

** Rolling friction is much smaller than the kinetic friction.

Centripetal and Centrifugal Force:

Centripetal Force: when body travels along a circular path , an external force always act on body towards the Centre of path, called centripetal force. f=(m*v^2)/R

ex: stone attached to a string, motion of planet, motion of electron around the nucleus in an atom, banking of road.

Centrifugal Force: equal and opposite of centripetal force, also called Psudo force or inertial force.

ex: Cream separator, 

Moment of Force: 

product of magnitude of force and perpendicular distance of direction of force from the axis of rotation.

Centre of Gravity:

** Centre of gravity of body doesn't change with the change in orientation of body in space.

Equilibrium:

Resultant of all force acting on a body is equal to zero.

if a body is in equilibrium, it will be either at rest or in uniform motion. if it is at rest, the equilibrium is called static, otherwise dynamic.

Condition of static equilibrium:

• Centre of gravity of the body should be at minimum height.
• The vertical line passing through the Centre of gravity of the body should pass through the base of body.