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Chapter 2Chapter 2
MotionMotion
Think About It!Think About It!
How would you describe speed?How would you describe speed?What would you need to know to figure out What would you need to know to figure out
speed?speed?Do you need to see something move to Do you need to see something move to
know that motion has occurred?know that motion has occurred?
Motion and PositionMotion and Position
A A reference pointreference point is needed to determine is needed to determine positionposition
MotionMotion: occurs when an object changes : occurs when an object changes position relative to a reference pointposition relative to a reference point
You are moving in your chairYou are moving in your chairRelative to the other planets!Relative to the other planets!Earth travels 942 billion meters/ year. Earth travels 942 billion meters/ year.
How fast is it traveling in mi/hr?How fast is it traveling in mi/hr?
Distance and DisplacementDistance and Displacement
Distance:Distance: how far an object has moved how far an object has movedkm, m, cm, etc.km, m, cm, etc.Displacement:Displacement: distance AND direction of distance AND direction of
object from starting pointobject from starting point
Distance and DisplacementDistance and Displacement
SpeedSpeed
Speed:Speed: distance traveled in a certain distance traveled in a certain amount of timeamount of time
Constant vs. Changing SpeedConstant vs. Changing Speed If speed is If speed is constantconstant – can calculate speed – can calculate speed
over any distance – it’ll be the same!over any distance – it’ll be the same! Usually speed is changingUsually speed is changing
Average SpeedAverage Speed Calculate Calculate total distancetotal distance by by total timetotal time
Instantaneous SpeedInstantaneous Speed
Def:Def: speed at a given point in time. speed at a given point in time. Speedometers show inst. speedSpeedometers show inst. speed Constant speed = inst. speed does not changeConstant speed = inst. speed does not change
Practice ProblemsPractice Problems
Runner travels 200m dash in 22 s. What Runner travels 200m dash in 22 s. What is the average speed?is the average speed?
You had an average speed of 70 mi/hr You had an average speed of 70 mi/hr from the St. Leon exit to the Harrison exit from the St. Leon exit to the Harrison exit on I-74. It took you 10 minutes to get on I-74. It took you 10 minutes to get there. How many miles did you travel?there. How many miles did you travel?
You traveled 75 miles at 70 mi/hr from You traveled 75 miles at 70 mi/hr from here to Indianapolis. How long did it take here to Indianapolis. How long did it take you in minutes?you in minutes?
VelocityVelocity
Def:Def: speed of object AND speed of object AND directiondirection speed : velocity speed : velocity asas distance : displacement distance : displacement Velocity can change even if speed is Velocity can change even if speed is
constantconstant
Moving ContinentsMoving Continents
GraphingGraphing
Time on X-AXISTime on X-AXIS Distance on Y-AXISDistance on Y-AXIS Constant speed = Constant speed =
straight linestraight line
GraphingGraphing Slope = Slope = change in ychange in y = = riserise = = distance distance = speed= speed
change in x run change in x run time time Horizontal line = object at restHorizontal line = object at rest
AccelerationAcceleration
Section 2Section 2
AccelerationAcceleration
Def: Def: rate of change of velocityrate of change of velocityCould be change in speed, direction or Could be change in speed, direction or
bothbothSpeeding up Speeding up + acceleration+ accelerationSlowing down Slowing down -- acceleration -- accelerationSpeed is changing = accelerationSpeed is changing = acceleration
AccelerationAcceleration
+ acc. = going in + acc. = going in same direction as same direction as velocityvelocity
-- acc. = going in -- acc. = going in opposite direction as opposite direction as velocityvelocity
AccelerationAcceleration
Changing direction is Changing direction is changing velocity and changing velocity and accelerationacceleration
Speed is constantSpeed is constant
CalculationsCalculations
If direction doesn’t change velocity = speedIf direction doesn’t change velocity = speed Units: m/sUnits: m/s22
Positive AccelerationPositive Acceleration
Jet airliner starts at rest and reaches a speed of Jet airliner starts at rest and reaches a speed of 80m/s in 20s. Calculate the acceleration.80m/s in 20s. Calculate the acceleration.
Has positive slope on graphHas positive slope on graph
Negative AccelerationNegative Acceleration
Skateboarder comes to rest in 2s after a speed Skateboarder comes to rest in 2s after a speed of 3 m/s. What is his acceleration?of 3 m/s. What is his acceleration?
Has negative slope on graphHas negative slope on graph
Time CalculationsTime Calculations
A car had a negative acceleration of 4 A car had a negative acceleration of 4 m/sm/s22 when it stopped after having a rate of when it stopped after having a rate of 40 m/s. How long did it take for the car to 40 m/s. How long did it take for the car to stop? stop?
Final Velocity CalculationsFinal Velocity Calculations
If a vehicle has an initial velocity of 35 m/s If a vehicle has an initial velocity of 35 m/s accelerates at 20 m/saccelerates at 20 m/s22 for 5 seconds, what for 5 seconds, what is it’s final velocity?is it’s final velocity?
Motion and ForcesMotion and Forces
Section 3Section 3
What is force?What is force?
Def:Def: a push or pull a push or pullKicking a ball, throwing a ball, etc.Kicking a ball, throwing a ball, etc.Chair has a force on you, atmosphere’s Chair has a force on you, atmosphere’s
force, etc.force, etc.
Changing MotionChanging Motion
Force causes motion Force causes motion to changeto change
Balanced ForcesBalanced Forces Net Force:Net Force: combination of two or more forces combination of two or more forces
act on an object at same time.act on an object at same time. Balanced Forces:Balanced Forces: forces equal in size but in forces equal in size but in
opposite directionopposite direction Net force = 0Net force = 0
Unbalanced ForcesUnbalanced Forces
Unequal opposite forcesUnequal opposite forces - net force will be the - net force will be the difference between the two and move in difference between the two and move in direction of bigger force direction of bigger force
Same Direction ForcesSame Direction Forces
Net force is sum of Net force is sum of the two and moves in the two and moves in that directionthat direction
Inertia and MassInertia and Mass
InertiaInertia: tendency to resist any change in : tendency to resist any change in motionmotion
Stop a bowling ball vs. ping pong ballStop a bowling ball vs. ping pong ballGreater massGreater mass of object of object greater inertiagreater inertiaNewton’s 1Newton’s 1stst Law of Motion Law of Motion
Newton’s 1Newton’s 1stst Law of Motion Law of Motion
Sir Isaac Newton (1642-1727)Sir Isaac Newton (1642-1727)Def:Def: Object moving at constant velocity Object moving at constant velocity
keeps moving at that velocity unless an keeps moving at that velocity unless an unbalanced net for actsunbalanced net for acts
Sometimes called “Law of Inertia”Sometimes called “Law of Inertia”
Car CollisonsCar Collisons
Seat belt vs. No seat beltSeat belt vs. No seat beltSpeed of 50 km/hr collides with wallSpeed of 50 km/hr collides with wallCar stops in .1sCar stops in .1sNo belt = person keeps moving at 50 No belt = person keeps moving at 50
km/hrkm/hrSeat belt = slows person to stop (air bags Seat belt = slows person to stop (air bags
help too)help too)