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)