Ch 11 Ch 11 MotionMotion

MotionMotion A change in position A change in position How do you know something has moved?How do you know something has moved?

Frame of reference (reference point) = Frame of reference (reference point) = system of objects that are not moving with system of objects that are not moving with respect to one anotherrespect to one another

Relative Motion = movement in relation Relative Motion = movement in relation (or relative)(or relative) to a frame of referenceto a frame of reference

DistanceDistance versus versus DisplacementDisplacement Distance is the length of a path Distance is the length of a path

between two pointsbetween two points SI Unit is meter (m)SI Unit is meter (m)

Displacement is the length Displacement is the length from the starting point to the from the starting point to the ending pointending point

Examples:Examples:

What is the total displacement?

4m + 2m + 4m + 2m = 12mWhat is the total distance traveled?

ZERO

How is the speed limit measured?How is the speed limit measured?

Miles per hourMiles per hour What 2 things are What 2 things are

considered?considered?

–Distance (miles)Distance (miles)

–Time (hour)Time (hour)

SpeedSpeed the ratio of the distance (d) the ratio of the distance (d)

an object moves to the an object moves to the amount of time (t) the object amount of time (t) the object movesmoves

SI Unit is meter per second SI Unit is meter per second (m/s)(m/s)

V=d/t, d=Vt, t=d/VV=d/t, d=Vt, t=d/V

Distance

Velocity time

SpeedSpeed

Average speed = computed for Average speed = computed for the entire duration of the tripthe entire duration of the trip

Instantaneous speed = measured Instantaneous speed = measured at a particular instantat a particular instant

Florence Griffith Joyner set a world Florence Griffith Joyner set a world record by running 200m in 21.34s. record by running 200m in 21.34s. What was her average speed?What was her average speed?

9.37 m/s9.37 m/s

Sound travels at a speed of 330m/s. If Sound travels at a speed of 330m/s. If a lightning bolt strikes the ground a lightning bolt strikes the ground 1000m away from you, how long will it 1000m away from you, how long will it take for the sound to reach you?take for the sound to reach you?

3.03 s3.03 s

Velocity (V) = the speed & Velocity (V) = the speed & direction an object is direction an object is movingmoving

Vector = a quantity that Vector = a quantity that has magnitude & direction has magnitude & direction

Same speed & direction = velocity

Distance-Time graphDistance-Time graph Slope tells me SPEED!Slope tells me SPEED! Horizontal part tells me the Horizontal part tells me the object object

stopped moving=no motion=no velocitystopped moving=no motion=no velocity Straight portions tell me Straight portions tell me constantconstant

speedspeed Greater the slope the higher the speed, Greater the slope the higher the speed,

vice versa vice versa

Graphing speedGraphing speed distance-time graph

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m)

Distance-Time GraphsDistance-Time GraphsConstant High Speed

0100200300400500

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time (s)

distan

ce (m

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Constant low speed

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Distance-Time GraphsDistance-Time GraphsVarying Speed

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No motion=stopped

STAR cards

What is a reference point? An objects that is not movingAn objects that is not moving

What are the units for speed?What are the units for speed? Meters per secondMeters per second

What does the horizontal line What does the horizontal line on a Distance-Time graph on a Distance-Time graph mean?mean?

That the object is not in motion, it’s stillThat the object is not in motion, it’s still

Acceleration Acceleration Is the Is the raterate at which velocity at which velocity

changeschanges changes in speedchanges in speed changes in directionchanges in direction changes in speed & directionchanges in speed & direction SI unit is meter per second per SI unit is meter per second per

second (m/ssecond (m/s22))

AccelerationAcceleration The triangle is the The triangle is the

Greek symbol Greek symbol delta, means delta, means “change in”“change in”

Vf = final velocityVf = final velocity Vi = initial velocity Vi = initial velocity Vf-Vi Vf-Vi

(final minus initial)(final minus initial) t

Va

Δ V

a t

Vf – Vi

SI unit is meter per second per second (m/sSI unit is meter per second per second (m/s22))

Why are the seconds squared?

Which car has greatest acceleration?•The blue car undergoes the greatest acceleration bc its velocity is changing at a more drastic rate •The red car is actually not accelerating at all. It has a constant velocity the entire race.

Distance-Time graph for the cars, Which car goes with which line?

Red=B

Blue=A

Green=C

Distance-Time Graph Distance-Time Graph

Changing Velocity over time

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Curved parts tells me object is Curved parts tells me object is increasing & decreasing speed = increasing & decreasing speed = changing velocity over a time periodchanging velocity over a time period= acceleration= acceleration

Speed-Time graphSpeed-Time graph Slope tells me acceleration!Slope tells me acceleration! Horizontal part tells me object is Horizontal part tells me object is

at at constantconstant speed (velocity) = no speed (velocity) = no accelerationacceleration

Slope downward tells me object Slope downward tells me object is slowing down (decelerating or is slowing down (decelerating or negative accleration)negative accleration)

Graphing constant accelerationGraphing constant acceleration Speed-Time Graph

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Speed-Time GraphSpeed-Time GraphPositive Acceleration

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Negative Acceleration

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spee

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Constant speed/velocity

STOPPED!

The speed limit changes from 55m/s The speed limit changes from 55m/s to 0m/s. To make the change in to 0m/s. To make the change in 10s, what acceleration will it 10s, what acceleration will it require?require?

A car’s acceleration is 3m/sA car’s acceleration is 3m/s22. if the . if the car started at rest and it only took car started at rest and it only took 10s for the car to reach this 10s for the car to reach this acceleration, what is the car’s final acceleration, what is the car’s final velocity?velocity?

A=9.8m/sA=9.8m/s22

Vf=0.5m/sVf=0.5m/s Vi=?Vi=? t=3st=3s

STAR cards What is a vector? a quantity that has magnitude & directiona quantity that has magnitude & direction What is acceleration? Is the Is the raterate at which velocity changes at which velocity changes What does horizontal part on a speed-time graph tell

me? object is at constant speed (velocity) = no accelerationobject is at constant speed (velocity) = no acceleration What does horizontal part of a distance-time graph tell

me? No speed, no motion, object is stoppedNo speed, no motion, object is stopped What does curved part on a distance-time graph tell

me? AccelerationAcceleration