Force and Friction Ust

HISTORY OF FORCE…..

ARISTOTLE - Natural world has 4 elements- air, water, earth and fire. Objects move because of their innate tendency to find their natural place.

JOHANNAS PHILOPONUS (550 AD) - If I exert an impetus, an object moves. Impetus keeps a body moving.

JEAN BURIDEN (355 AD) – When impetus diminishes, motion also diminishes. When impetus is removed, object stops moving.

GALILEO GALILEI– showed that the bodies were accelerated by gravity to an extent which was independent of their mass and argued that objects retain their velocity unless acted on by a force, for example friction.

AND SIR ISAAC NEWTON CAME….“ If I have been

able to see a little father than other men, it is because

I have stood on the shoulders of

giants “

and the rest is history…

is a push or a pull

quantitative description of the interaction between to bodies

Force does not always cause motion.

It does not mean that forces acting on an object will always cause it to move.

Forces can produce changes in motion. Net force cause an object at rest to start moving.

Net force causes a moving object to stop. Force causes an object to change its direction.

Sum of the forces acting on a body.

a contact force

Acts on surfaces of two bodies

Force that opposes the motion of the body

The component parallel to the surface.

Static friction – frictional force enough to prevent relative motion between surfaces in contact.

Sliding or kinetic friction- occurs when there is relative motion at the interface of the surfaces in contact

Rolling friction- takes place when one surface rotates as it moves over another surface but does not slide or slip.

Depends on the following:

Kind of surface

mass of the object

velocity of the object

area of contact

f = Nf = friction= coefficient of frictionN = normal force

-Use rough surface-Make use of heavy materials-increase the velocity-increase the area of contact

- oiling or lubricating-Use of bearings-Streamlining-Magnetic levitation

FRIC