FRICTION

• KAJAL D. THACKER : - 120850106001

• MANSI J. THACKER :- 120850106042

• HARPAL JADEJA : - 120850106014

• AMAN BHIMAN :- 120850106039

FRICTION OR FRICTION FORCE

WHEN A BODY SLIDE OR TENDS TO SLIDE ON A SURFACE ON WHICH IT IS RESTING,A RESTING FORCE OPPOSING THE MOTION IS PRODUCED AT THE CONTACT SURFACE .THIS RESTING FORCE IS CALLED FRICTION OR FRICTION FORCE

NEWTON’S 1ST LAW

AN OBJECT AT REST STAYS AT REST AND IN MOTION STAYS AT MOTION WITH THE SAME SPEED AND IN THE SAME DIRECTION UNLESS ACTED UPON BY AN UNBALANCED FORCES

CONDITION OF FRICTION FORCES

FRCTION FORCES (F),ALWAYS ACT IN THE DIRECTION OPPOSITE TO THE MOVEMENT OF THE BODY

IF CONTACT SURFACE IS SMOOTH ,FRICTION FORCE (F) WILL BE LESS

IF CONTACT SURFACE IS ROUGH, FRICTION FORCE (F) WILL BE MORE

IN MACHINE PARTS LIKE PISTON, BEARINGS, LINER ETC……ATTEMPTS ARE MADE TO REDUCE FRICTION TO INCRESE LIFE OF PARTS AND EFFICIENCY OF MACHINE.

OUTER SURFACE OF VEHICLE TYRES IS MADE ROUGH TO INCREASE FRICTION BETWEEN TYRE AND ROAD SURFACE FOR SAFE DRIVING.

LIMITING FRICTION

THE MAXIMUM FRICTION FORCE THAT CAN BE DEVELOPED AT THE CONTACT SURFACE ,WHEN BODY IS JUST ON THE POINT OF MOVING IS CALLED LIMITING FORCE OF FRICTION.

TYPES OF FRICTION

STATIC FRICTION

DYNAMIC FRICTION - SLIDING FRICTION - ROLLING FRICTION

STATIC FRICTION :-

FRICTION EXPERIENCED BY A BODY WHEN IT IS AT REST IT IS CALLED STATIC FRICTION.

IN CASE OF STATIC FRICTION ,

P < F WHERE P = EXETERNAL FORCE F = FRICTION FORCE THERE IS NO MOTION .

DYNAMIC FRICTION :-

FRICTION EXPERIENCED BY A BODY WHEN IT IS CALLED DYNAMIC FRICTION

DYNAMIC FRICTION < STATIC FRICTION

SLIDING FRICTION :- FRICTION EXPERIENCED BY A BODY WHEN IT SLIDES OVER ANOTHER BODY , IT IS CALLED SLIDING FRICTION.

FOR EXAMPLE :-

-TO PUSH THE TABLE ON THE FLOOR .

ROLLING FRICTION :- FRICTION EXPERIENCED BY A BODY WHEN IT ROLLS OVER ANOTHER BODY IS CALLED ROLLING FRICTION.

FOR EXAMPLE :-

-TO MOVE THE DRUM BY ROOLING.- BALL BEARING USED IN MACHINE.

ANGLE OF FRICTION

THE ANGLE BETWEEN NORM AL (N) AND RESULTANT FORCE (R) IS CALLED ANGLE OF FRICTION

IT IS ALSO CALLED LIMITING ANGLE OF FRICTION THE VALUE OF ‘θ’ IS MORE FOR ROUGH SURFACE AS COMPARE TO SMOOTH SURFACE .

COEFFICIENT OF FRICTION : (µ)

LIMITING FRICTION (F) IS PROPORSTIONAL TO THE NORMAL REACTION (N),

F α N

F = µ*N

µ=F/N ………..(1)

THE RATIO OF LIMITING FRICTION (F) AND NORMAL REACTION (N) IS CALLED COEFFICIENT OF FRICTION

TAN θ = F/N …………(2)

FROM EQUATION (1) AND (2)

TAN θ = µ

• COEFFICIET OF STATIC FRICTION :-

IT IS DEFINED AS RATIO OF THE LIMITING FFRICTION FORCE (F) TO THE NORMAL REACTIONTHE (N) OFFERED TO TE BODY BY THE SURFACE , PROVIDED THE BODY IS IN IMPENDIND CONDITION

µs = Fs/N

• COEFFICIENT OF KINETIC FRICTION:-

IT IS DEFINED AS THE RATIO OF FRICTION FORCE (F) DEVELOPED WHILE THE BODY IS IN MOTION TO THE NORMAL REACTION (N) DEVELOPED

µk = Fk/N

ANGLE OF REPOSE WITH INCREASE IN ANGLE OF

THE INCLINED SURFACE THE MAXIMUM ANGLE AT WHICH , BODY STARTS SLIDIND DOWN IS CALLED ANGLE OF REPOSE .

RESOLVE PERPENDICULAR TO PLANE

N = WCOS ø RESOLVE PARALLEL TO THE PLANE

F = W SIN ø µ = F/N = W SIN α / WCOS α

µ = TAN ø ………..(1)

WE KNOW THAT ,

µ = TAN θ ………….(2) FROM EQUATION (1) AND (2)

θ = ø ,

WHERE α = ANGLE OF INCLINED PLANE

HENCE , WHEN THE ANGLE OF INCLINED PLANE (ø ) ,BECOMES EQUAL TO LIMITING ANGLE OF (θ ) , BODY WILL SLIDE DOWN THE PLANE.

ANGLE OF REPOSE = ANGLE OF FRICTION = .

EXAMPLES OF ANGLE OF REPOSE

CONE OF FRICTION

IT IS DEFINED AS AN IMAGINARY CONE FORMED BY REVOLVING THE RESULTANT (R) OF THE NORMAL REACTION (N) AND LIMITING FRICTION AL FORCE (F) ABOUT THE NORMAL REACTION (N) FOR ONE COMPLETE REVOLUTION .

EXPLANATION OF CONE OF FRICTION IF BODY IS IN LIMITING

EQUILIBRIUM THE RESULTANT REACTION R MAKES AN ANGLE ø THE HIGHT OF CONE HENCE WHEN THE LIMITING FRICTION IS OFFERED THE LINE OF ACTION OF R SHOULD ALWAYS LIE ON TE SURFACE OF AN INVERTED RIGHT CIRCULAR CONE WHOSE SEMI VERTEX ANGLE IS ø.

AS LONG AS THE RESULTANT LIES WITHIN OR ALONG THE PERIPHERY OF THE SURFACE OF CONE THE BODY WILL BE AT REST AS SOON AS THE RESULTANT CROSSES THE PERIPHERY OF THE CONE THE BODY COMES IN MOTION

EXAMPLES OF CONE FRICTION

VARIATION OF FRICTION WITH APPLIED FORCE(P) CONSIDER A HEAVY

BLOCK RESTING ON ROUGH SURFACE .AS THE VALUE OF P INCREASES .THE FRICTIONAL FORCE (F) ALSO INCREASES UP TO CERTAIN VALUE OF FORCE (P) THE BLOCK WILL NOT MOVE

WHEN FRICTION FORCE REACHES LIMITING VALUE THE BLOCK WILL START MOVING IN THE DIRECTION OF FORCE .

THERE IS SLIGHT DECREASE IN THE VALUE OF FRICTION FORCE WHEN BODY IS IN MOTION

CATEGORIES OF FRICTIONAL FORCE STATIC FRICTION FORCE (F) IF BODY IS IN EQUILIBRI LIMITING FRICTION FORCE WHEN BODY JUST START MOVING . KINETIC FRICTION FORCE WHEN BODY IS IN MOTION .

LAWS OF STATIC FRICTION FOLLOWING ARE THE LAWS OF STATIC FRICTION

1. THE FRICTION FORCE ALWAYS ACT IN A DIRECTION OPPOSITE TO THAT IN WHICH THE BODY TENDS TO MOVE

2. THE MAGNITUDE OF FRICTION FORCE IS EQUAL TO THE EXETERNAL FORCE

3. THE RATIO OF LIMITING FRICTION (F) AND NORMAL REACE FRITTION (N) IS CONSTANT

4. THE FRICTION FORCE DOES NOT DEPENDS UPONE THE AREA OF CONSTANT BETWEEN THE TWO SURFACE

5. THE FRICTION FORCE DEPENDS UPONE THE ROUGHNESS OF THE SURFACE

LAWS OF DYNEMIC FRICTION

•THE FRICTION FORCE ACT IN THE DIRECTION, OPPOSITE TO THAT IN WHICH THE BODY IS MOVING . •THE RATIO OF LIMITING FRICTION (F) AND NORMAL REACTION (N) IS CONSTANT & IT IS KNOWN AS CO-EFFICIENT OF FRICTION •FOR MODERATE SPEED THE FRICTION FORCE REMAINS CONSTANT BUT IT DECREASES SLIGHTILY WITH THE INCREASES OF SPEED.

LADDER FRICTION THE LADDER IS A DEVICE FOR CLIMBING OR

SCALLING ON THE ROOFS OR WALLS IT IS MADE OF WOOD OR IRON THERE ARE TO LONG PIECES IN THE LADDER TO WHICH MANY SMALL CROSS PIECES CALLED RUGS ARE CONNECTED AT EQUAL DISTANCE TO WORK AS STEPS

•SELF WEIGT OF LADDER IS (W)•WEIGHT OF MAN STANDING ON THE LADDER •REACTION BY THE FLOOR ON THE LADDER (RA)•FRICTION FORCE BETWEEN LADDER AND FLOOR IS RA=µ* RA

•REACTION BY WALL ON THE LADDER IS RB

•FRIC TION FORCE BETWEEN LADDER AND WALL IS FB=RB*µ

EXAMPLES OF LADDER FRICTION

WEDGE FRICTION

A WEDGE IS USUALLY OF A TRIANGULAR OR TRAPEZ OIDAL IN CROSS SECTION . IT IS GENERALLY USED FOR SLIGHT ADJUSTMENT IN THE POSIITION