Usain Bolt is the world’s fastest man!!!
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Usain Bolt is the world’s fastest man!!!
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Usain Bolt is the world’s fastest man!!!. Physics of Motion. We will look at: Distance Displacement Speed First you need to realize that motion is relative…. Motion is relative. What is meant by saying that motion is relative? For everyday motion, what is motion usually relative to?. - PowerPoint PPT Presentation
Transcript of Usain Bolt is the world’s fastest man!!!
Usain Bolt is the world’s fastest man!!!
Physics of MotionPhysics of Motion
We will look at:We will look at:– DistanceDistance– DisplacementDisplacement– SpeedSpeed
First you need to realize that motion First you need to realize that motion is relative…is relative…
Motion is relativeMotion is relative
What is meant by saying that motion What is meant by saying that motion is relative? For everyday motion, is relative? For everyday motion, what is motion usually relative to?what is motion usually relative to?
Motion is RelativeMotion is Relative
Motion is relative to the observer’s Motion is relative to the observer’s position and their reference pointposition and their reference point– Sometimes called a “reference frame”Sometimes called a “reference frame”
Consider the picture…
• If this man is driving at 15 mph, how fast is his coffee cup moving?
•Does the man feel like the cup is moving?
•Why?
DirectionDirection
We use N, S, E, W We use N, S, E, W to describe the to describe the direction of direction of movement.movement.
Distance and DisplacementDistance and DisplacementDistance measures the Distance measures the actual path an object takesactual path an object takes
Displacement measures Displacement measures your overall distance from your overall distance from the starting point in a the starting point in a STRAIGHT LINE.STRAIGHT LINE.
DISPLACEMENT values must DISPLACEMENT values must include a DIRECTION!include a DIRECTION!
Which color line represents Which color line represents distance?distance?
Displacement?Displacement?
Distance vs. DisplacementDistance vs. Displacement
http://www.physics.gatech.edu/academics/classes/2211/main/demos/displacement/DDis.html
SpeedSpeed
Describes how fast an object moves.Describes how fast an object moves.
We know some things move faster We know some things move faster than others…but how do we measure than others…but how do we measure it?it?
What two quantities must you know What two quantities must you know to determine speed?to determine speed?
What two quantities must you What two quantities must you know to determine speed?know to determine speed?
Choose from: displacement, Choose from: displacement, distance, time, velocitydistance, time, velocity– Hint…what is speed measured in???Hint…what is speed measured in???
– Speed= distance/timeSpeed= distance/timeEx- miles/hour, m/s, etc. Ex- miles/hour, m/s, etc.
There are three types of speed There are three types of speed you must know…you must know…
Constant speedConstant speed
Average speedAverage speed
Instantaneous speedInstantaneous speed
But first let’s look at some But first let’s look at some graphs…graphs…
If I wanted to graph speed, what should I If I wanted to graph speed, what should I label my axes???label my axes???
So the slope of the line=SPEEDSo the slope of the line=SPEED
Dis
tanc
e
Time
Speed
Constant SpeedConstant Speed
When an object covers equal When an object covers equal distances in equal amounts of timedistances in equal amounts of time
Ex- if a race car travels at a Ex- if a race car travels at a CONSTANT SPEED of 96m/s, it will CONSTANT SPEED of 96m/s, it will travel a DISTANCE of 96 meters travel a DISTANCE of 96 meters EVERY SECOND.EVERY SECOND.
Constant SpeedConstant Speed
What would a d-t graph look like for a What would a d-t graph look like for a constant speed?constant speed?
But most objects do not travel at But most objects do not travel at a constant speed.a constant speed.
The speed of an object can change from The speed of an object can change from one minute to another.one minute to another.
So we can use So we can use AVERAGE SPEED AVERAGE SPEED to to describe its motion.describe its motion.
Use this equation…Use this equation…
Average Speed = total Distance / total TimeAverage Speed = total Distance / total Time
Let’s try itLet’s try it
A runner finished a 3 mile race in 22 A runner finished a 3 mile race in 22 minutes. He may not have run at the minutes. He may not have run at the same pace the whole time, but you same pace the whole time, but you can still calculate his AVERAGE can still calculate his AVERAGE SPEEDSPEED
22 minutes / 3 miles = 7.33 min/mile 22 minutes / 3 miles = 7.33 min/mile
Instantaneous vs. Average speedInstantaneous vs. Average speed
Average speed-Average speed- overall distance overall distance over time the object traveledover time the object traveled
Instantaneous speed-Instantaneous speed- measures measures speed over small time interval (at an speed over small time interval (at an instant)instant)
Does a speedometer of a car read Does a speedometer of a car read instantaneous or average speed?instantaneous or average speed?
What 2 controls on a car enable a What 2 controls on a car enable a change in speed? change in speed?
Let’s use our math skillsLet’s use our math skills
Page 323…Page 323…
Read through “MATH SKILLS”Read through “MATH SKILLS”
DO problems 1-3 “Practice Problems”DO problems 1-3 “Practice Problems”
Answers to problems on 323Answers to problems on 323
1. v=d/t1. v=d/t110m/72 sec= 1.5 m/s toward shore110m/72 sec= 1.5 m/s toward shore
2.2.v=d/tv=d/t
38m/1.7 sec= 22m/s toward first base38m/1.7 sec= 22m/s toward first base
3.3.d=vt=(12.0 km/hr)(5.00 hr)d=vt=(12.0 km/hr)(5.00 hr)
= 6.00 x 10= 6.00 x 1044 m m
What if I want to describe speed What if I want to describe speed AND direction?AND direction?
For example…what if you wanted to For example…what if you wanted to find a plane. Knowing the speed find a plane. Knowing the speed would only tell you how far away to would only tell you how far away to look but not in what direction. For look but not in what direction. For that we need…that we need…
VELOCITY- the speed and direction of VELOCITY- the speed and direction of motion.motion.
Let’s get back to the car Let’s get back to the car example…example…
Name another control that enables a Name another control that enables a change in velocity.change in velocity.
In order to analyze such situations, we need to understand what are known as
vectors…All measured quantities can be
classified as being either a scalar or a vector.
Scalar
_________ only (size of the quantity ….a number)
Vector
_________ and _________
Magnitude Magnitu
deDirection
Speed is Velocity…kind of…Speed is Velocity…kind of…• Velocity is the vector for the scalar of Velocity is the vector for the scalar of
speed.speed.• The magnitude is the same!!! The magnitude is the same!!! • Therefore in calculations, you can use speed or Therefore in calculations, you can use speed or
velocity interchangeablyvelocity interchangeably
• Speed = Speed = distance / timedistance / time
• Velocity = Velocity = distance / time distance / time in a directionin a direction
• http://www.youtube.com/watch?http://www.youtube.com/watch?v=DRb5PSxJerM&feature=relatedv=DRb5PSxJerM&feature=related
Use the diagram to determine the resulting Use the diagram to determine the resulting displacement and the distance traveled by displacement and the distance traveled by
the skier during these three minutes. the skier during these three minutes.
AnswerAnswer
The skier covers a distance ofThe skier covers a distance of
(180 m + 140 m + 100 m) = (180 m + 140 m + 100 m) = 420 m420 m and has a displacement of and has a displacement of 140 m, 140 m, rightwardrightward..
What is the coach's resulting What is the coach's resulting displacement and distance of displacement and distance of
travel? travel?
AnswerAnswer
The coach covers a distance ofThe coach covers a distance of
(35 yds + 20 yds + 40 yds) = (35 yds + 20 yds + 40 yds) = 95 95 yardsyards and has a displacement of and has a displacement of 55 55 yards, left.yards, left.
Consider a car moving with a constant, rightward (+) velocity of 10 m/s.
How many meters will he travel in 5 How many meters will he travel in 5 seconds?seconds?
Constant velocityConstant velocity
Now consider a car moving with a Now consider a car moving with a rightward (+), changing velocityrightward (+), changing velocity - -
that is, a car that is moving rightward but speeding up or that is, a car that is moving rightward but speeding up or acceleratingaccelerating..
AccelerationAcceleration
Distance time graphsDistance time graphs
Draw 2 graphsDraw 2 graphs– One showing a slow constant speedOne showing a slow constant speed– One showing a faster constant speedOne showing a faster constant speed
Slow, Rightward(+)Slow, Rightward(+)Constant VelocityConstant Velocity
Fast, Rightward(+)Fast, Rightward(+)Constant VelocityConstant Velocity
Slow, Leftward(-)Slow, Leftward(-)Constant VelocityConstant Velocity
Fast, Leftward(-)Fast, Leftward(-)Constant VelocityConstant Velocity
Consider a car moving with a Consider a car moving with a constant, rightward (+) velocityconstant, rightward (+) velocity - say of - say of +10 m/s. A car moving with a constant velocity is a car with zero +10 m/s. A car moving with a constant velocity is a car with zero
acceleration.acceleration.
Draw a graph!Draw a graph!
Constant velocity = zero Constant velocity = zero accelerationacceleration
Now consider a car moving with a rightward (+), changing velocity - that is, a car that is moving rightward but speeding up or accelerating. Since the car is
moving in the positive direction and speeding up, the car is said to have a positive acceleration.
Positive accelerationPositive acceleration
Describe this graph!Describe this graph!
Does the velocity of the wind affect Does the velocity of the wind affect such things as a sprinter’s speed or such things as a sprinter’s speed or an airplane’s flight time?an airplane’s flight time?
Resultant Velocity animationResultant Velocity animation
http://www.glenbrook.k12.il.us/http://www.glenbrook.k12.il.us/GBSSCI/PHYS/mmedia/vectors/GBSSCI/PHYS/mmedia/vectors/plane.htmlplane.html
A small airplane heads east with a speed of 200 mph with respect to the air (the “air speed”). This would be the plane’s speed if the air was NOT moving – no wind)
• If the wind/jet stream is moving east at 50 mph, what is the plane’s resulting velocity with respect to the ground (the “ground speed”)?
““Adding Vectors” Example:Adding Vectors” Example:
with the wind
200 50
250 mph, east
• If, later, the airplane is flying west into the 50 mph wind with an “air speed” of 200 mph, now what is the plane’s resulting velocity with respect to the ground (the “ground speed”)?
against the wind
50
200
150 mph, west
1.1. Find the velocity in m/s of a Find the velocity in m/s of a swimmer who swims 110 m toward swimmer who swims 110 m toward the shore in 72 s.the shore in 72 s.
1.5 m/s toward the shore1.5 m/s toward the shore
1.1. Imagine that you could ride a Imagine that you could ride a baseball that is hit high enough and baseball that is hit high enough and far enough for a home run. Using far enough for a home run. Using the baseball as a reference frame, the baseball as a reference frame, what does the Earth appear to do?what does the Earth appear to do?
1.1. Calculate the displacement in Calculate the displacement in meters a cyclist would travel in 5.00 meters a cyclist would travel in 5.00 h at an average velocity of 12.0 h at an average velocity of 12.0 km/h to the southwest.km/h to the southwest.
