1) Force =~ Force Is an external effort which may move a bedy at ‘est or stop a moving body or change the speed of a ‘moving body or change the direction of 2 moving body or ‘change the shape and size of a body. Effects of force = |) Force can move abody at rest. 1) Force can stop a moving body, ti) Force can change the speed of a moving body. iv) Force can change the direction of a moving body. ¥) Free can change the shape and size ofa hody. pido 3) Force of friction Force of ction ste force which opposes the motion of an object over asurface, Eg: A ball olin on ground gradually slows down and ‘comes to a stop due to force of eton. ‘we stop pedaling a bieyco, kt gradually slows ‘down and comes toa tap due to fore ction roe {an object with uniform motion wil continue to move with uniform mation ha forces acting on (pushing fres and rtonaforea} Wan unbalanced fore acts onthe moving body, them ts speed or rection of mation changes. {1 tho unbalanced force is removed, then it will continuo te move with the Speed tha acqulred tl then 2) Balanced and unbalanced forces :~ ‘) Balanced forces {orces ae eaua, fen the resuitant fre acting onthe boy 20. Balanced frees cannot change the stat of rest or motion of {wo fre ct na Bay nope direction and one aces ‘Such forces are called unbalanced forces, ‘Unbalinced forces changes the state of rst othe mtion of body. 4) Galileo's expe ‘en a marble ale down a ined plane volt creates and when goer upon te soconainctnad pana, elochydncrestan, tha wenatons [bite plane sre egul thnthe mara wi ace tae blght which t ‘led down Ht incination ofthe second planes dacosse. kw ave! ‘tore distance te Yech the nina eight the nciaton the secon plane ‘Fade atone marble wile forever tying foreach he sama ‘olorcatenudnaisnaintheaniom moto attvo maiSN ws of Newton s first law of motion states that - “An object remains ina state of rest or in uniform motion in a straight ied to change that state by an applied Inortia:~ Tho natural tondeney of objects to romain in a state of rest or in uniform motion is ealed inertia, ‘This is why the frst law of motion Is aIso known 2s the faw of inemtia ea no —_ 6) Inertia and Mass : pis hired meas eet motion continues to be in motion. This property of a body Is called its inertia, force required to change the state of the body, The force required to change the state of a heavier body is more than the force required to change the state of the lighter body. This is because the mass of the heavier body is, ‘more than the mass of the lighter body. So ‘The mass of a body is a measure ofits inertia.’ ‘owes outané dust inertia ofr, theater cor fal down ita ean placed ona playing card evra tumblers Nicted wit the 1) When we valine car andthe diver apes the bras auddany, we tn tafaliforward aie ier of motion, a Wh wo ar slanting ina bus ante bus beginsto move Sdn, we tnd ofa bockrard because ou fot a eenact wt the te ope pat canes oven 7) Momentum of a body ‘The momentum of a body is the product of its mass and velocity. ‘Momentum = mass x velocity p=my where pis the momentum of a body mis the mass of the body vis the velocity of the body Ifa body is at rest its valocity is zero and so its momentum is also zero, The St unit of momentum is kilogram metre per second or kg mis or kg ms* Eg -A truck moving ata very low speed can kill a person standing in tts path because of the heavy mass ofthe truck. ‘bulla of small mats when fred from a gun en killa pareon because of the large velocity ofthe bullet. ‘So the impact ofa body depends upon its mass and veloc.'8) Newton’s second law of motion eee a ed nar sane papas once senses Corerterre ee SUSAR iat eT Initial momemtum p= mu Final momentum p, = my ‘Change in momentum p,~p, = mv — ms =miy-u) Rate of change of momentum =mre=aT- fi Crthe applied foree Fa WTV=UT or F = KORTU=U) bul W=u) =a ‘So F=kma where kis a constant of proportionality or F=ma ‘The Stunt of mass is kg. and aecelaration ie mis or ms? a0 the unit of Foren le gms! or nowion i's symbol is ‘Examples of action and reaction += 1) en» bullets fred tom agun,K exer a torward fore (ation) on {he bullet andthe ute exerts an equal snd oppose foree on the gyn (tevin) ether eo 1) Wena salr jumps out of boat, he exerts a backward force of the boat action) and the boat exerts an equal and opposite free en tho 10) Newton’s third law of motion :~ ‘Newton's third aw of motan ste that To every action there is an equal and opposte reaction and they at on two ailferent bodies ‘To.prove that action and reaction are equal and opposite :~ “ako two spring balances A and B connected toga. isthe sping balance 80. gid support. When a forces applied by pulling he tree {nd of tha spring balance A bath the spring balances shew the same ‘endings This shows that the force exerted by the spring balance Aon Bis equal but opposite indirection tothe force exerted By spring balance 8 on A. The force exetod by the spring batsnee Aon Bis ‘ction and the fores exerted bythe spring balance Bon Ai reaction, liywnenanair filed baloon released, the force of he at coming out ‘ofthe balloon actin) svorts an eyual ad opposite orcs on the bilo reaction) and It moves upward Iwy¥mnen a rockets tre, ne frce of he buming gases coming out (action exerts an equal and opposte force onthe racket (action) and Wnowes upward