MotionSpeedVelocity and Acceleration

8/17/2019 MotionSpeedVelocity and Acceleration

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Motion, Speed,Motion, Speed,

Velocity andVelocity andAccelerationAcceleration



MotionMotion

►MotionMotion – an object’s change in– an object’s change in

position relative to a reference pointposition relative to a reference point



Reference PointReference Point

► The Earth’s srface is sed as a The Earth’s srface is sed as a

co!!on reference pointco!!on reference point

►A !oving object can be sed as aA !oving object can be sed as a

reference point as "ellreference point as "ell



SpeedSpeed

►SpeedS

peed is the distance traveled dividedis the distance traveled divided

by the ti!e interval dring "hich theby the ti!e interval dring "hich the

!otion occrred!otion occrred

►#or!ally, objects do not travel at a#or!ally, objects do not travel at a

constant speedconstant speed

►Average Speed $Average Speed $ total distancetotal distance

total ti!etotal ti!e



Which Distance?Which Distance?

► %ar!er &ones drives ' !iles do"n a straight%ar!er &ones drives ' !iles do"n a straight

road( She trns arond and drives ) !ilesroad( She trns arond and drives ) !iles

bac*( +hat "as her average speed for thisbac*( +hat "as her average speed for this

trip if it too* hor-trip if it too* hor-



.or ans"er to this proble! .or ans"er to this proble!

depends on yor interpretation ofdepends on yor interpretation of/distance traveled/( .o cold say0/distance traveled/( .o cold say0

► The The total distancetotal distance traveled by %ar!er &ones istraveled by %ar!er &ones is1 !iles( Therefore her average speed is 11 !iles( Therefore her average speed is 1!i2hr(!i2hr(

► The The net distancenet distance traveled by %ar!er &ones is 3traveled by %ar!er &ones is 3!iles( Therefore, her average speed is 3 !i2hr(!iles( Therefore, her average speed is 3 !i2hr(

► There are good reasons to se either There are good reasons to se eitherinterpretation $ it4s !ostly a !atter of preference(interpretation $ it4s !ostly a !atter of preference(+e "ill interpret /distance traveled/ to be+e "ill interpret /distance traveled/ to be netnetdistancedistance ((also calledalso called displacement).di

splacement). %ar!er%ar!er &ones4 average speed "as 3 !i2hr( &ones4 average speed "as 3 !i2hr(



VelocityVelocity

►VelocityVelocity is the speed of an object in ais the speed of an object in a

particlar directionparticlar direction

►

5!agine t"o birds leave the sa!e tree5!agine t"o birds leave the sa!e tree

at the sa!e ti!e( The both 6y atat the sa!e ti!e( The both 6y at

1*!2hr for 7 !intes( +hy don’t1*!2hr for 7 !intes( +hy don’t

they end p at the sa!e place-they end p at the sa!e place-





VelocityVelocity

►VelocityVelocity appears to be very si!ilar toappears to be very si!ilar to

speed, ho"ever, "hen describing thespeed, ho"ever, "hen describing the

velocity of an object yo need tovelocity of an object yo need to

provide a !agnitde and a directionprovide a !agnitde and a direction

►MagnitudeMagnitude – the speed of the object– the speed of the object

►DirectionDirection – the direction the object is– the direction the object is

!oving!oving



VelocityVelocity

►E89 A bs has a velocity of :7!iles2hrE89 A bs has a velocity of :7!iles2hr

heading "estheading "est



Resltant VelocityResltant Velocity

►An object can have a resltant velocityAn object can have a resltant velocity

if it is e8periencing !ore than oneif it is e8periencing !ore than one

!otion(!otion(

►%or e8a!ple if a person "al*s do"n the%or e8a!ple if a person "al*s do"n the

center of a bs "hile it is in !otioncenter of a bs "hile it is in !otion

there are t"o velocities occrring(there are t"o velocities occrring(

( The !ove!ent of the bs( The !ove!ent of the bs 3( The !ove!ent of the person inside the3( The !ove!ent of the person inside the

bsbs



E8a!pleE8a!ple

7 !2s + !2s = ) !2s



E8a!pleE8a!ple

7 !2s + = !2s ' !2s



AccelerationAcceleration

►AccelerationAcceleration is the rate at "hichis the rate at "hich

velocity changes over ti!evelocity changes over ti!e An object accelerates if its speed, direction,An object accelerates if its speed, direction,

or both changeor both change

►Average acceleration =

nal velocity ! starting velocity

time it ta"es to change velocity



AccelerationAcceleration

►E8a!pleE8a!ple

A car on the high"ay is traveling 77 !i2hrA car on the high"ay is traveling 77 !i2hr

and it passes another car( 5n order toand it passes another car( 5n order to

pass, the car has to accelerate to '7pass, the car has to accelerate to '7!i2hr( The car reaches this velocity )1!i2hr( The car reaches this velocity )1

seconds later( +hat is the averageseconds later( +hat is the average

acceleration of the car-acceleration of the car-



Acceleration and VelocityAcceleration and Velocity

►http022"""(glenbroo*(*3(il(s2;<SS=52Phttp022"""(glenbroo*(*3(il(s2;<SS=52P

>.S2!!edia2*ine!a2avd(ht!l>.S2!!edia2*ine!a2avd(ht!l►As velocityAs velocity increasesincreases, so does, so does

accelerationacceleration►As velocityAs velocity decreasesdecreases, so does, so does

accelerationacceleration

►+hen direction changes, so does+hen direction changes, so doesaccelerationacceleration

►+hen there is a+hen there is a constant velocityconstant velocity, there, there

is no accelerationis no acceleration

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/kinema/avd.html






MotionSpeedVelocity and Acceleration

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