FORCES AND THEIR EFFECTS

A PRESENTATION ON FORCES.

FORCESA FORCE IS ANY INTERACTION THAT, WHEN UNOPPOSED, WILL CHANGE THE MOTION OF AN OBJECT. IN OTHER WORDS, A FORCE CAN CAUSE AN OBJECT WITH MASS TO CHANGE ITS VELOCITY (WHICH INCLUDES TO BEGIN MOVING FROM A STATE OF REST), I.E., TO ACCELERATE. FORCE CAN ALSO BE DESCRIBED BY INTUITIVE CONCEPTS SUCH AS A PUSH OR A PULL. A FORCE HAS BOTH MAGNITUDE AND DIRECTION, MAKING IT A VECTOR QUANTITY. IT IS MEASURED IN THE SI UNIT OF NEWTONS AND REPRESENTED BY THE SYMBOL F.THE ORIGINAL FORM OF NEWTON'S SECOND LAW STATES THAT THE NET FORCE ACTING UPON AN OBJECT IS EQUAL TO THE RATE AT WHICH ITS MOMENTUM CHANGES WITH TIME. IF THE MASS OF THE OBJECT IS CONSTANT, THIS LAW IMPLIES THAT THE ACCELERATION OF AN OBJECT IS DIRECTLY PROPORTIONAL TO THE NET FORCE ACTING ON THE OBJECT, IS IN THE DIRECTION OF THE NET FORCE, AND IS INVERSELY PROPORTIONAL TO THE MASS OF THE OBJECT.

MOTION

MOTION IS A CHANGE IN POSITION OF AN OBJECT WITH RESPECT TO TIME. MOTION IS TYPICALLY DESCRIBED IN TERMS OF DISPLACEMENT, DISTANCE (SCALAR), VELOCITY, ACCELERATION, TIME AND SPEED. MOTION OF A BODY IS OBSERVED BY ATTACHING A FRAME OF REFERENCE TO AN OBSERVER AND MEASURING THE CHANGE IN POSITION OF THE BODY RELATIVE TO THAT FRAME.IF THE POSITION OF A BODY IS NOT CHANGING WITH RESPECT TO A GIVEN FRAME OF REFERENCE THE BODY IS SAID TO BE AT REST, MOTIONLESS, IMMOBILE, STATIONARY, OR TO HAVE CONSTANT (TIME-INVARIANT) POSITION. AN OBJECT'S MOTION CANNOT CHANGE UNLESS IT IS ACTED UPON BY A FORCE, AS DESCRIBED BY NEWTON'S FIRST LAW. MOMENTUM IS A QUANTITY WHICH IS USED FOR MEASURING MOTION OF AN OBJECT. AN OBJECT'S MOMENTUM IS DIRECTLY RELATED TO THE OBJECT'S MASS AND VELOCITY, AND THE TOTAL MOMENTUM OF ALL OBJECTS IN AN ISOLATED SYSTEM (ONE NOT AFFECTED BY EXTERNAL FORCES) DOES NOT CHANGE WITH TIME, AS DESCRIBED BY THE LAW OF CONSERVATION OF MOMENTUM.

GRAVITY

GRAVITY OR GRAVITATION IS A NATURAL PHENOMENON BY WHICH ALL THINGS WITH ENERGY ARE BROUGHT TOWARD (OR GRAVITATE TOWARD) ONE ANOTHER, INCLUDING STARS, PLANETS, GALAXIES AND EVEN LIGHT AND SUB-ATOMIC PARTICLES. GRAVITY IS RESPONSIBLE FOR MANY OF THE STRUCTURES IN THE UNIVERSE, BY CREATING SPHERES OF HYDROGEN — WHERE HYDROGEN FUSES UNDER PRESSURE TO FORM STARS — AND GROUPING THEM INTO GALAXIES. ON EARTH, GRAVITY GIVES WEIGHT TO PHYSICAL OBJECTS AND CAUSES THE TIDES. GRAVITY HAS AN INFINITE RANGE, ALTHOUGH ITS EFFECTS BECOME INCREASINGLY WEAKER ON FARTHER OBJECTS.GRAVITY IS MOST ACCURATELY DESCRIBED BY THE GENERAL THEORY OF RELATIVITY (PROPOSED BY ALBERT EINSTEIN IN 1915) WHICH DESCRIBES GRAVITY NOT AS A FORCE BUT AS A CONSEQUENCE OF THE CURVATURE OF SPACETIME CAUSED BY THE UNEVEN DISTRIBUTION OF MASS/ENERGY; AND RESULTING IN GRAVITATIONAL TIME DILATION, WHERE TIME LAPSES MORE SLOWLY IN LOWER (STRONGER) GRAVITATIONAL POTENTIAL. HOWEVER, FOR MOST APPLICATIONS, GRAVITY IS WELL APPROXIMATED BY NEWTON'S LAW OF UNIVERSAL GRAVITATION, WHICH POSTULATES THAT GRAVITY CAUSES A FORCE WHERE TWO BODIES OF MASS ARE DIRECTLY DRAWN (OR 'ATTRACTED') TO EACH OTHER ACCORDING TO A MATHEMATICAL RELATIONSHIP, WHERE THE ATTRACTIVE FORCE IS PROPORTIONAL TO THE PRODUCT OF THEIR MASSES AND INVERSELY PROPORTIONAL TO THE SQUARE OF THE DISTANCE BETWEEN THEM. THIS IS CONSIDERED TO OCCUR OVER AN INFINITE RANGE, SUCH THAT ALL BODIES (WITH MASS) IN THE UNIVERSE ARE DRAWN TO EACH OTHER NO MATTER HOW FAR THEY ARE APART.

FRICTION

FRICTION IS THE FORCE RESISTING THE RELATIVE MOTION OF SOLID SURFACES, FLUID LAYERS, AND MATERIAL ELEMENTS SLIDING AGAINST EACH OTHER. THERE ARE SEVERAL TYPES OF FRICTION:• DRY FRICTION RESISTS RELATIVE LATERAL MOTION OF TWO SOLID SURFACES IN CONTACT. DRY FRICTION IS

SUBDIVIDED INTO STATIC FRICTION("STICTION") BETWEEN NON-MOVING SURFACES, AND KINETIC FRICTION BETWEEN MOVING SURFACES.

• FLUID FRICTION DESCRIBES THE FRICTION BETWEEN LAYERS OF A VISCOUS FLUID THAT ARE MOVING RELATIVE TO EACH OTHER.[2][3]

• LUBRICATED FRICTION IS A CASE OF FLUID FRICTION WHERE A LUBRICANT FLUID SEPARATES TWO SOLID SURFACES.• SKIN FRICTION IS A COMPONENT OF DRAG, THE FORCE RESISTING THE MOTION OF A FLUID ACROSS THE SURFACE

OF A BODY.• INTERNAL FRICTION IS THE FORCE RESISTING MOTION BETWEEN THE ELEMENTS MAKING UP A SOLID MATERIAL

WHILE IT UNDERGOES DEFORMATION.WHEN SURFACES IN CONTACT MOVE RELATIVE TO EACH OTHER, THE FRICTION BETWEEN THE TWO SURFACES CONVERTS KINETIC ENERGY INTO THERMAL ENERGY (THAT IS, IT CONVERTS WORK TO HEAT). THIS PROPERTY CAN HAVE DRAMATIC CONSEQUENCES, AS ILLUSTRATED BY THE USE OF FRICTION CREATED BY RUBBING PIECES OF WOOD TOGETHER TO START A FIRE. KINETIC ENERGY IS CONVERTED TO THERMAL ENERGY WHENEVER MOTION WITH FRICTION OCCURS, FOR EXAMPLE WHEN A VISCOUS FLUID IS STIRRED. ANOTHER IMPORTANT CONSEQUENCE OF MANY TYPES OF FRICTION CAN BE WEAR, WHICH MAY LEAD TO PERFORMANCE DEGRADATION AND/OR DAMAGE TO COMPONENTS. FRICTION IS A COMPONENT OF THE SCIENCE OF TRIBOLOGY.

NEWTON'S LAWS OF MOTION

NEWTON'S LAWS OF MOTION ARE THREE PHYSICAL LAWS THAT, TOGETHER, LAID THE FOUNDATION FOR CLASSICAL MECHANICS. THEY DESCRIBE THE RELATIONSHIP BETWEEN A BODY AND THE FORCES ACTING UPON IT, AND IT'S MOTION IN RESPONSE TO THOSE FORCES. THEY HAVE BEEN EXPRESSED IN SEVERAL DIFFERENT WAYS, OVER NEARLY THREE CENTURIES, AND CAN BE SUMMARIZED AS FOLLOWS.FIRST LAW:WHEN VIEWED IN AN INERTIAL REFERENCE FRAME, AN OBJECT EITHER REMAINS AT REST OR CONTINUES TO MOVE AT A CONSTANT VELOCITY, UNLESS ACTED UPON BY A FORCE.SECOND LAW:THE VECTOR SUM OF THE FORCES F ON AN OBJECT IS EQUAL TO THE MASS M OF THAT OBJECT MULTIPLIED BY THE ACCELERATION VECTOR A OF THE OBJECT: F = MA.THIRD LAW:WHEN ONE BODY EXERTS A FORCE ON A SECOND BODY, THE SECOND BODY SIMULTANEOUSLY EXERTS A FORCE EQUAL IN MAGNITUDE AND OPPOSITE IN DIRECTION ON THE FIRST BODY.

THE THREE LAWS OF MOTION WERE FIRST COMPILED BY ISAAC NEWTON IN HIS PHILOSOPHIÆ NATURALIS PRINCIPIA MATHEMATICA (MATHEMATICAL PRINCIPLES OF NATURAL PHILOSOPHY), FIRST PUBLISHED IN 1687. NEWTON USED THEM TO EXPLAIN AND INVESTIGATE THE MOTION OF MANY PHYSICAL OBJECTS AND SYSTEMS. FOR EXAMPLE, IN THE THIRD VOLUME OF THE TEXT, NEWTON SHOWED THAT THESE LAWS OF MOTION, COMBINED WITH HIS LAW OF UNIVERSAL GRAVITATION, EXPLAINED KEPLER'S LAWS OF PLANETARY MOTION.

MADE BY: ASAD ALI