# PHYSICS NOTES.docx - PHYSICS NOTES CHAPTER 2: MOTION IN A...

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PHYSICS NOTESCHAPTER 2: MOTION IN A STRAIGHT LINE2.1 SCALARS AND VECTORSMagnitude: the size or extent of something. A quantitative measure expressed as a number of a standardunit.Scalarquantities: a physical quantity that is represented by a magnitude and units only.Examples; distance, time, speed, volumeVectorquantities: a physical that requires magnitude, units, and a direction in order to be fully defined. Velocity,acceleration and force are examples of vector quantities.Examples; force, velocity, acceleration, displacementNewton(N) – unit of measure for forceADDING VECTORSDraw vectors from head to tailResultantvector: sum of the vectors, from tail of the first vector to head of the last vectorThe sign of the final magnitude gives the direction of the final vectorSUBTRACTING VECTORSSubtract the initial vector from the final vectorReverse the sign of the initial vectoroAdd the reversed initial velocity to the final velocityvfvi=vf+(vi)=vDraw the finalvelocityfirst, then draw the negative of the initial velocityoResultant vector =v2.2 DISPLACEMENT, SPEED AND VELOCITYCentre of mass: point at which the mass of an object is considered to be concentrated for the purpose of analysingmotionPosition: the location of an object at a certain point in time with respect to the origin, a vector quantityDisplacement: the change in position of an object, represented by the symbols, a vector quantityThe route taken between the start and finish is not considereds= final position – initial positionTotal displacement = sum of individual displacementsVelocity: the ratio of displacement to time taken, a vector quantity. The rate at which displacement changes.Direction of velocity = direction of displacementAveragespeed= average velocity if moving in a straight linevav=d∆tvav=s∆tResultant vector =vector a +vector b
2.3 ACCELERATIONAcceleration: the rate of change of velocity, a vector quantityA measure of how quickly velocity changesAcceleration can be caused by a change in speed or a change in directionchangespeed=final speedinitial speed∆ v=vuv=finalvelocityinitial velocity¿vuNegative acceleration – slowing down or speeding up in the opposite directionaav=changevelocitychangetime¿vt¿vut2.4 GRAPHING POSITION, VELOCITY AND ACCELERATION OVER TIMEPosition/displacement – time graphs:Gradient = velocityoPos gradient = pos velocityoNeg gradient = neg velocityFor a curved position-time graph;oInstantaneous velocity = gradient of the tangent to the line at a particular pointoAverage velocity = gradient of the cord between start and end points of a periodVelocity – time graphs:When the graph is below the x-axis, velocity is negativeoTravel in the opposite directionDisplacement = area between the curve and the x-axisoTotal displacement = sum of all the signed displacementsAverage acceleration = gradient over a time intervaloInstantaneous acceleration = gradient of the tangent to the curve at the point of interestDistance travelled = sum of all the magnitudes of the areas above and below the x-axisoTotal distance = sum of all the magnitudes of the areasAbsolute value the valuesAcceleration – time graphsArea gives a change in velocityvvaluearea=a×∆t=vAverage acceleration is the gradient of the chord between two pointsInstantaneous acceleration is the gradient of the tangent to the line at the point of interest

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