Motion. Motion Motion is the change of an object’s position over time Motion is the change of an...

MotionMotion

MotionMotion

Motion is the change of an object’s Motion is the change of an object’s position over timeposition over time

When we say something has moved, When we say something has moved, we are describing motionwe are describing motion

When we are describing motion, we When we are describing motion, we are comparing it to a frame of are comparing it to a frame of referencereference

Motion ActivityMotion Activity

On your graph paper, draw a small On your graph paper, draw a small picture of yourself getting ready to picture of yourself getting ready to take a walk in the center at the top.take a walk in the center at the top.

The center is West (Draw a dot)The center is West (Draw a dot)You are going to walk 10 squares to You are going to walk 10 squares to

the right to Mario’s for a slice of pizzathe right to Mario’s for a slice of pizzaHow far have you moved from West?How far have you moved from West?How far have you traveled?How far have you traveled?

Motion ActivityMotion Activity

You forgot your physical science You forgot your physical science notebook, so you have to run home notebook, so you have to run home 14 squares in the other direction and 14 squares in the other direction and get itget itHow far have you moved from West?How far have you moved from West?How far (total squares) have you How far (total squares) have you

traveled?traveled?

Motion ActivityMotion ActivityYou don’t want to be late for Physical You don’t want to be late for Physical

Science, so you run 4 squares back Science, so you run 4 squares back to Westto WestHow far have you moved from How far have you moved from

West?West?This is displacementThis is displacement

How far (total squares) have you How far (total squares) have you traveled?traveled?This is distanceThis is distance

Distance vs. DisplacementDistance vs. Displacement

Distance – the length of the path Distance – the length of the path traveled between the initial and final traveled between the initial and final positions of something in motionpositions of something in motion

Displacement – the shortest distance Displacement – the shortest distance between the initial and final positions between the initial and final positions of something in motionof something in motion

SpeedSpeed

When we talk about how fast When we talk about how fast something is traveling, we are talking something is traveling, we are talking about speedabout speed

Speed is the rate at which an object Speed is the rate at which an object movesmoves

SpeedSpeed

How do we calculate speed?How do we calculate speed?

t

dv

Distance

Velocity Time

t

dv

t

dv

t

dv

t

ds

SpeedSpeed

How do we calculate speed?How do we calculate speed?

Distance

Speed Time

SpeedSpeedDistanceDistance is usually measured in is usually measured in m or kmm or kmTimeTime is usually measured in is usually measured in s or hrs or hrThe The unit of speed unit of speed is usually is usually m/s or km/hrm/s or km/hrSpeed is used to describe anything that is Speed is used to describe anything that is

changing position:changing position:Runners, carsRunners, carsOcean currents, windsOcean currents, windsMoon, EarthMoon, Earth

Constant SpeedConstant Speed

Some objects have speeds that stay Some objects have speeds that stay the same as they movethe same as they moveConstant speedConstant speed

Speed does not changeSpeed does not changePlot the distance vs. time for a Plot the distance vs. time for a

cheetah traveling 30m/s for 5 secondscheetah traveling 30m/s for 5 seconds


A cheetah A cheetah running at running at constant constant speedspeed

Time (s)Time (s) Distance (m)Distance (m)

00 00

11 3030

22 6060

33 9090

44 120120

55 150150


Constant Speed

0

30

60

90

120

150

0 1 2 3 4 5

Time (s)

Dis

tan

ce (

m)

Average SpeedAverage Speed

Some objects have speeds that change Some objects have speeds that change as they moveas they moveWe have to calculate average speedWe have to calculate average speed

Speed changes over timeSpeed changes over timeThink about driving in a carThink about driving in a car

Speed limit changesSpeed limit changesStop signs and stoplightsStop signs and stoplights


Time (s)Time (s) Distance (m)Distance (m)

00 00

11 3030

22 7575

33 9090

44 130130

55 150150

A car in the pick-up line at West

Average SpeedAverage SpeedAverage Speed

0

30

60

90

120

150

0 1 2 3 4 5

Time (s)

Dis

tan

ce (

m)


For things moving at a constant For things moving at a constant speed, the speed at any point on speed, the speed at any point on the line is the the line is the average speedaverage speed

Instantaneous SpeedInstantaneous Speed

For things moving at any speed, For things moving at any speed, the speed at a given point in time the speed at a given point in time is the is the instantaneous speedinstantaneous speed

VelocityVelocity

VelocityVelocity is a speed is a speed in a given directionin a given directionIf you drive to Raleigh, your average If you drive to Raleigh, your average

speed could be 97km per hr speed could be 97km per hr

(60miles per hr)(60miles per hr)Your velocity would be 97 km per hr Your velocity would be 97 km per hr

easteastYou have to include the directionYou have to include the direction

Speed and Velocity PracticeSpeed and Velocity Practice

An airplane flew 1000 km in 4 hr. An airplane flew 1000 km in 4 hr. What is the airplane’s speed?What is the airplane’s speed?


A car travels 50 km west in 30 A car travels 50 km west in 30 minutes. What is its velocity in minutes. What is its velocity in km/hr?km/hr?


How long will it take a ball to roll How long will it take a ball to roll 26m if its velocity is 2.0m/s to the 26m if its velocity is 2.0m/s to the right?right?


If a runner moves with a speed of If a runner moves with a speed of 1.5m/s and changes her speed to 1.5m/s and changes her speed to 2.1m/s over 3s, what is her 2.1m/s over 3s, what is her average speed over that 3s?average speed over that 3s?


Work on Velocity ProblemsWork on Velocity Problems

AccelerationAcceleration

Think about riding a roller coasterThink about riding a roller coaster You go up the first hill at constant speedYou go up the first hill at constant speed After the top of the hill, your speed increases After the top of the hill, your speed increases

quicklyquickly At the bottom of the hill, you slow down and At the bottom of the hill, you slow down and

make some turns and keep goingmake some turns and keep going Rapid changes in velocityRapid changes in velocity The rate of change in velocity is The rate of change in velocity is accelerationacceleration


Something that is speeding up, slowing down, Something that is speeding up, slowing down, or changing direction is acceleratingor changing direction is accelerating

Acceleration= Acceleration= Final velocity-original velocityFinal velocity-original velocity

TimeTimeWhat are the units of acceleration?What are the units of acceleration?Acceleration tells you how fast velocity is Acceleration tells you how fast velocity is

changingchanging


Sample Problem: What is the Sample Problem: What is the acceleration if we speed up from 10m/s acceleration if we speed up from 10m/s to 30 m/s in 10 seconds?to 30 m/s in 10 seconds?

A = A = VVf - V- Vi

tt


Sample Problem: A roller coaster car speeds Sample Problem: A roller coaster car speeds up as it goes down a hill. As it starts down up as it goes down a hill. As it starts down the hill, its speed is 8m/s, and at the bottom the hill, its speed is 8m/s, and at the bottom of the hill 3 seconds later, its speed is of the hill 3 seconds later, its speed is 28m/s. What is its average accleration?28m/s. What is its average accleration?

A = A = VVf - V- Vi

tt

GravityGravity

Gravity is the acceleration of an object Gravity is the acceleration of an object toward Earthtoward Earth

g=9.8m/sg=9.8m/s22

GravityGravity

Example: Brandon drops a water balloon out a Example: Brandon drops a water balloon out a window on Dominic, who is standing below. window on Dominic, who is standing below. If it takes 10 seconds for the balloon to If it takes 10 seconds for the balloon to reach Dominic’s head, what is its speed just reach Dominic’s head, what is its speed just before it hits Dominic?before it hits Dominic?

g = 9.8m/sg = 9.8m/s22 - put in place of acceleration - put in place of acceleration

g = g = VVf - V- Vi What is Vi?

tt

MomentumMomentum

Think about a football gameThink about a football gameA 100kg fullback runs up the field and A 100kg fullback runs up the field and

collides with an 80 kg defensive back. The collides with an 80 kg defensive back. The 100kg fullback gets knocked to the ground 100kg fullback gets knocked to the ground by the smaller player. How does that by the smaller player. How does that happen?happen?

The defensive back has more The defensive back has more momentummomentumAll moving objects have momentumAll moving objects have momentumThe more momentum a moving object has, The more momentum a moving object has,

the harder it is to stop.the harder it is to stop.

MomentumMomentum

If both players had the same velocity, which If both players had the same velocity, which player would have more momentum?player would have more momentum?

What are the units for momentum?What are the units for momentum?p = m x v (p is the abbreviation for p = m x v (p is the abbreviation for

momentum)momentum)Momentum has units of kgMomentum has units of kg·m/s·m/s

MomentumMomentum

Momentum depends on the mass of an Momentum depends on the mass of an object and its velocityobject and its velocityMomentum=Mass x VelocityMomentum=Mass x Velocityp=m x vp=m x v

In the football game, how can the smaller In the football game, how can the smaller player knock over the larger player?player knock over the larger player?His mass is smallerHis mass is smallerHis velocity must be largerHis velocity must be larger

MomentumMomentum

What are some things that have a large What are some things that have a large momentum?momentum?Train – has a very large massTrain – has a very large massCar – large mass, high speedCar – large mass, high speed

Harder to stop if moving fasterHarder to stop if moving fasterStopping distance is directly related to Stopping distance is directly related to

momentummomentumBullet – small mass, but high velocityBullet – small mass, but high velocity

Law of Conservation of MomentumLaw of Conservation of Momentum

When two objects collide, one object When two objects collide, one object transfers momentum to the othertransfers momentum to the other

The total momentum of a group of The total momentum of a group of objects stays the same unless outside objects stays the same unless outside forces act on the objectsforces act on the objectsNo momentum is lostNo momentum is lostTotal momentum is the sameTotal momentum is the same

Think about the football playersThink about the football players

Law of Conservation of MomentumLaw of Conservation of Momentum

How do moving objects act?How do moving objects act?Richard_Garriott_Space_Video_Blog_Richard_Garriott_Space_Video_Blog_

Conservation_of_Momentum.aviConservation_of_Momentum.aviExplains recoil of a gunExplains recoil of a gunhttp://www.batesville.k12.in.us/physics/phynet/mechanics/http://www.batesville.k12.in.us/physics/phynet/mechanics/

momentum/firing_a_gun.htmmomentum/firing_a_gun.htm

MythbustersMythbusters

Mythbusters - Lego ballMythbusters - Lego ballLego BallLego Ball

Motion. Motion Motion is the change of an object’s position over time Motion is the change of an...

Documents

Transcript of Motion. Motion Motion is the change of an object’s position over time Motion is the change of an...