2 Acceleration TermsAcceleration (a)– the rate of change of velocity (can be +, -, or centripetal)Deceleration– only negative acceleration (slowing down)Centripetal Acceleration– acceleration that occurs when changing direction (turning)Freefall– objects falling due to gravityForce is what you feel when you accelerate
3 3 ways to accelerateSince acceleration is a change in velocity and velocity has 2 partsWe can accelerate byChanges in speedSpeed up (+ acceleration)Slow down (- acceleration)Changing DirectionTurningChanging both speed and direction
4 Your speedometer – the key to accel We don’t see acceleration of an object well with our eyesBut if we look at a speedometer we can see speed change.Acceleration is a picture of what your speedometer is doing
5 Acceleration is a pic of your Speedo Slow AccelerationFast(er) AccelerationAcceleration is a pic of your Speedo
6 The Acceleration Graph Setup The VariablesThe GraphSpeed ( or velocity)is the dependent variableTime is the independent variableGraph setup = FormulaSpeedDspa=DtTimeThe Acceleration Graph Setup
9 Slope & Type of Acceleration Steeper slopes show greater accelerationStraight lines = Constant accelerationSteady increase or decrease in speedAccelerates quicklyspeedtspeedtdecelerates slowlyAccelerates slowlydecelerates quicklyWhen is the speed = to 0 (stopped)?
10 Discuss This graphDescribe which sport you think this graph represents and why.GolfSkydivingFishing100-meter dashDrag racingSpeedTime
11 Calculating Acceleration from Slope Rise–change in the graph on the vertical axis (Speed)Run–change in the graph on the horizontal axis (Time)Slope = =Y2-y1X2-x1riserunAcceleration=sp2-sp1t2-t1P1 (0 s, 0 km/h)t1 sp1P2 (20 s, 20 km/h)t sp2P2a=sp2-sp1t2-t1=20 km/h - 0 km/h20 s– 0 s20 km/h20 s=P1= 1 km/h/s
12 Answers to Sample Questions What is the acceleration of the object from 0 – 20 s?What is the speed of the object from 20 – 40 s?What is the speed of the object from 40 – 60 s?sp2 – sp 1 (rise)(20–0 m/s)20 m/sAcceleration(slope) ====1 m/s/st2 – t (run)( 20 – 0 s)20 ssp2 – sp 1 (rise)(20–20 m/s)0 m/sAcceleration(slope) ====0 m/s/st2 – t (run)( 40 – 20 s)20 ssp2 – sp 1 (rise)(0–20 m/s)-20 m/sAcceleration(slope) ====-1 m/s/st2 – t (run)( 60 – 40 s)20 s
13 Acceleration Formula, Units & Power Shape m/s, cm/min, km/hAcceleration=final speed – initial speedfinal time – intial timem/s/s, cm/min/min, km/h/ss, min, hrSince:sp2 = final speed, sp1 = initial speedt2 = final time, t1 = initial timea =(spf – spi)(tf – ti)a =(sp2 – sp1)(t2 – t1)
14 Acceleration Formula, Units & Power Shape =final speed – start speedfinal time – start timesp2=final speed, sp1=start speed t2=final time, t1=start timeSince: Then:÷Dspa =D spD tDsp = sp2 – sp1aDtDt = t2 – t1 or x
15 Using the Acceleration Power Shape or xaDtDsp÷A kid is sledding down a hill. When he enters the course his speed is 10 m/s. After 2 seconds he has reached a speed of 26 m/s. What was his acceleration?Given Formula Setup SolutionList Given InfoAnd Unknown:sp1 = 10 m/ssp2 = 26 m/sDt = 2 sa= ?Show Needed Equations:a =Substitute with Units & Show Math:a =Circles Answer with Units:a =a = 8 m/s/s(sp2 – sp1)26 m/s-10 m/s16 m/sDt2 s2 s
16 Freefall and gravitational acceleration Freefall: Objects falling due to gravityAll objects accelerate at the same rate due to gravity during freefall regardless of their massObjects may reach terminal velocity sooner due to air resistanceGravitational acceleration (g) = 9.8 m/s/s on earth
17 Using the Acceleration Power Shape or xaDtDsp÷A woman jumps from a plane. She opens her parachute five seconds later. How fast was she going when she opened her shoot (disregard air resistance)?Given Formula Setup SolutionList Given InfoAnd Unknown:Dsp = ??Dt = 5 sa= g=9.8 m/s/sShow Needed Equations:Dsp =Substitute with Units & Show Math:Dsp =Circles Answer with Units:Dsp = 49.2 m/sa· Dt9.8 m/s/s· 5 s
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