MotionMotion

Chapter 2 Chapter 2

Sections 1-3Sections 1-3

MotionMotion

Section 1 - Describing Motion Section 1 - Describing Motion slides 3- 21slides 3- 21

Section 2 - Acceleration Section 2 - Acceleration slides 22 – 28slides 22 – 28

Section 3 – Motion & Forces Section 3 – Motion & Forces slides 29 -41slides 29 -41

Section 1- Describing MotionSection 1- Describing Motion

What You’ll Learn:What You’ll Learn:

The difference between displacement & The difference between displacement & distancedistance

The difference between speed & velocityThe difference between speed & velocity

How to graph motionHow to graph motion

MotionMotion

Distance & time are important in describing a Distance & time are important in describing a race. The winner covers the distance in the race. The winner covers the distance in the shortest amount of time.shortest amount of time.

<http://images.stockcarracing.com/>

How are motion & position related?How are motion & position related?

A reference point is needed to tell where A reference point is needed to tell where something is or if it has moved.something is or if it has moved.

<http://farm3.static.flickr.com>

What is relative motion?What is relative motion?

Not all motion is obvious. When you are Not all motion is obvious. When you are sitting still, you appear not to be moving sitting still, you appear not to be moving although you are moving in relation to the although you are moving in relation to the Sun because you are sitting on Earth.Sun because you are sitting on Earth.Relative motion means that one thing Relative motion means that one thing moves in relation to another thing. Earth moves in relation to another thing. Earth is moving in space in relation to the Sun. is moving in space in relation to the Sun. The Sun is the reference point for the The Sun is the reference point for the Earth’s motion.Earth’s motion.

How are distance & displacement How are distance & displacement different?different?

Distance Distance is how far is how far something has moved. something has moved. The distance of a 50 The distance of a 50 m dash is 50 meters.m dash is 50 meters.

Displacement Displacement is the is the distance & direction of distance & direction of an object’s position an object’s position relative to the starting relative to the starting point.point. Running of the Bulls Running of the Bulls

(Pamplona, Spain) (Pamplona, Spain)

<www.tribuneindia.com><www.tribuneindia.com>

SpeedSpeed

To tell how fast something is moving, you need To tell how fast something is moving, you need to know how far it travels in a certain amount of to know how far it travels in a certain amount of time. time. Speed Speed is the distance an object travels per unit is the distance an object travels per unit of time.of time.

“Hundreds of people and six fighting bulls, accompanied by steer, sprinted the half-mile (850-meter) route through cobblestone streets in just over two minutes…” Associated Press 7-8-2008

Speed = 850m / 2 min= _______ m/s

How is speed calculated?How is speed calculated?

Speed = distance/time= m/sSpeed = distance/time= m/s

850m/ 2 min or 120 sec= 7.08 m/s850m/ 2 min or 120 sec= 7.08 m/s

We divide the distance traveled by the time it We divide the distance traveled by the time it took to travel the distance.took to travel the distance.

“Hundreds of people and six fighting bulls, accompanied by steer, sprinted the half-mile (850-meter) route through cobblestone streets in just over two minutes…” Associated Press 7-8-2008

Speed = 850m / 2 min= _______ m/s

What is motion with constant What is motion with constant speed? speed?

A speedometer measures the speed of a A speedometer measures the speed of a car. Suppose you look at it when you are car. Suppose you look at it when you are riding on a freeway. The car is not riding on a freeway. The car is not speeding up or slowing down; it is moving speeding up or slowing down; it is moving at a constant speed.at a constant speed.

<http://farm1.static.flickr.com/>

What is changing speed?What is changing speed?

Usually speed is not Usually speed is not constant. constant.

Here we see how the Here we see how the speed of a cyclist speed of a cyclist changes over 5 km.changes over 5 km.

The ride took 15 The ride took 15 minutes.minutes.

Speed Changing Over DistanceSpeed Changing Over Distance

2525

2020

1515

1010

55

00

Going downhill

Climbing steep hill

Gaining speed

Stopping for red light

Constant speed

Distance

Speed (km/hr)

What is average speed?What is average speed?

Average speedAverage speed is the total distance is the total distance traveled divided by the total time of travel. traveled divided by the total time of travel.

It is calculated using the relationships It is calculated using the relationships among speed, distance & time.among speed, distance & time.

Average speed= total distance / total time= Average speed= total distance / total time= 5 km/15 min or .25 hr= 20 km/hr.5 km/15 min or .25 hr= 20 km/hr.

What is instantaneous speed?What is instantaneous speed?

Instantaneous speedInstantaneous speed is the speed at one is the speed at one point in time, or one instant. point in time, or one instant.

If an object moves with constant speed, If an object moves with constant speed, the speed remains the same; however, if it the speed remains the same; however, if it speeds up or slows down, the speeds up or slows down, the instantaneous speed is changing.instantaneous speed is changing.

Graphing MotionGraphing Motion

A A distance- distance- time time graph graph shows the shows the motion of motion of an object an object over time.over time.

Graphing MotionGraphing Motion

The steepness of the The steepness of the line is its slope (m).line is its slope (m).

The slope of the line The slope of the line is the speed. A is the speed. A steeper slope means steeper slope means a greater speed.a greater speed.

Slope= rise/run or Slope= rise/run or ∆y/∆x∆y/∆x

<www.revisionworld.com>

How is changing speed graphed?How is changing speed graphed?

The changing slope in The changing slope in this graph indicates this graph indicates changing speed.changing speed.

Review graphing from Review graphing from Chapter 1 notes.Chapter 1 notes.

<http://honolulu.hawaii.edu/distance>

How do you draw a distance-time How do you draw a distance-time graph?graph?

Distance is plotted on the vertical (y) axis Distance is plotted on the vertical (y) axis & time is plotted on the horizontal (x) axis.& time is plotted on the horizontal (x) axis.

Each axis has a scale, or series of Each axis has a scale, or series of numbers, that covers the range of the numbers, that covers the range of the data.data.

Each axis is divided into equal parts; then Each axis is divided into equal parts; then the data points are plotted on the graph the data points are plotted on the graph and finally connected with a line.and finally connected with a line.

<http://www.batesville.k12.in.us/>

VelocityVelocity

Suppose there is a storm nearby traveling Suppose there is a storm nearby traveling at a speed of 20 km/h that is 20 km east of at a speed of 20 km/h that is 20 km east of your location. Will it reach you?your location. Will it reach you?

                                                                                                                                                                 

<Associated Press, 2008>

VelocityVelocity

Suppose there is a storm nearby traveling Suppose there is a storm nearby traveling at a speed of 20 km/h that is 20 km east of at a speed of 20 km/h that is 20 km east of your location. Will it reach you?your location. Will it reach you?

Knowing the speed is not enough; you Knowing the speed is not enough; you must also know the direction it is traveling.must also know the direction it is traveling.

VelocityVelocity is the speed of an object is the speed of an object andand the the direction it is moving.direction it is moving.

How do speed & direction affect How do speed & direction affect velocity?velocity?

Two escalators may move at the same Two escalators may move at the same speed even though one goes up and the speed even though one goes up and the other travels down.other travels down.

Because they move in opposite directions Because they move in opposite directions their velocity is different despite having the their velocity is different despite having the same speed.same speed.

Velocity depends on both speed and Velocity depends on both speed and direction.direction.

<http://farm1.static.flickr.com/>

Motions of Earth’s CrustMotions of Earth’s Crust

Some motion is so slow that it is hard to Some motion is so slow that it is hard to see such as plate tectonics. Geologic see such as plate tectonics. Geologic evidence shows that the continents have evidence shows that the continents have moved over millions of years.moved over millions of years.

The plates of the lithosphere slide on the The plates of the lithosphere slide on the softer layers below manifesting softer layers below manifesting themselves as earthquakes, volcanic themselves as earthquakes, volcanic eruptions and formation of mountains.eruptions and formation of mountains.The plates along San Andreas Fault speed along at about 1 cm/yr!The plates along San Andreas Fault speed along at about 1 cm/yr!

<http://geology.com/articles/images/san-andreas-fault-line.jpg>

Section 2 - AccelerationSection 2 - Acceleration

What You’ll Learn:What You’ll Learn:

How acceleration, time & velocity are How acceleration, time & velocity are relatedrelated

How positive & negative acceleration How positive & negative acceleration affect motionaffect motion

How to calculate accelerationHow to calculate acceleration

Acceleration, Speed, & VelocityAcceleration, Speed, & Velocity

Acceleration Acceleration is the rate of change of is the rate of change of velocity. When velocity changes, the velocity. When velocity changes, the object is accelerating.object is accelerating.

Speed is the rate of change of position.Speed is the rate of change of position.

Remember velocity includes both speed & Remember velocity includes both speed & direction.direction.

How are speeding up & slowing How are speeding up & slowing down described?down described?

Speeding up & slowing Speeding up & slowing down are both down are both accelerating. accelerating.

The first is positive and The first is positive and the second is negative.the second is negative.

Acceleration has Acceleration has direction, just like direction, just like velocity. velocity.

<http://physicsed.buffalostate.edu/>

Does changing direction affect Does changing direction affect acceleration?acceleration?

The speed of The speed of a horse a horse moving moving around a around a carousel carousel remains remains constant, but constant, but because it is because it is changing changing direction it is direction it is accelerating.accelerating.

Calculating AccelerationCalculating Acceleration

Find the change in velocity by subtraction.Find the change in velocity by subtraction.

∆∆V= final V – initial V or VV= final V – initial V or Vff – V – Vii

Then, to find acceleration, divide ∆V by the Then, to find acceleration, divide ∆V by the length of time during the velocity change.length of time during the velocity change.

Acceleration (Acceleration (αα)= ∆v or V)= ∆v or Vff – V – Vi i /time (t)/time (t)

where ∆ means change, V is velocity, where ∆ means change, V is velocity, αα is acceleration, etc. is acceleration, etc.

Calculating AccelerationCalculating Acceleration

The SI unit for velocity is meters/sec (m/s).The SI unit for velocity is meters/sec (m/s).

To find acceleration, velocity is divided by time in To find acceleration, velocity is divided by time in seconds (s).seconds (s).

The unit for acceleration is m/sThe unit for acceleration is m/s2.2.

<www.ubergizmo.com/>

Amusement Park AccelerationAmusement Park Acceleration

Roller coasters are exciting rides because Roller coasters are exciting rides because their designers use the laws of physics.their designers use the laws of physics.

The steep drops and loops of steel roller The steep drops and loops of steel roller coasters give the rider large accelerations coasters give the rider large accelerations by using gravity and sharp turns.by using gravity and sharp turns.

static.howstuffworks.com/gif/roller-coaster-2...

Section 3 – Motion & ForcesSection 3 – Motion & Forces

What You’ll Learn:What You’ll Learn:

How force & motion are relatedHow force & motion are related

Newton’s first law of motionNewton’s first law of motion

What forces & motion are present during a What forces & motion are present during a car crashcar crash

What is force?What is force?

ForceForce is a push or a is a push or a pull like kicking a pull like kicking a soccer ball.soccer ball.Sometimes it isn’t so Sometimes it isn’t so obvious. Can you obvious. Can you feel gravity holding feel gravity holding you in place?you in place?You exert force when You exert force when you sit, stand, stretch, you sit, stand, stretch, bend, push or pull.bend, push or pull.

<http://www.thephysicaledge.com/>

How does force change motion?How does force change motion?

What happens to the What happens to the motion of the ball motion of the ball when the racket hits when the racket hits it?it?

<http://www.mnsun.com/>

How does force change motion?How does force change motion?

What happens to the What happens to the motion of the ball motion of the ball when the racket hits when the racket hits it?it?

The force of the The force of the racket makes the ball racket makes the ball stop and then move in stop and then move in a different direction.a different direction.

<http://www.mnsun.com/>

What are balanced forces?What are balanced forces?

When 2 or more When 2 or more forces act on an forces act on an object at the same object at the same time, the combined time, the combined force is called force is called net net force. force. Forces that Forces that are equal in size & are equal in size & opposite in direction opposite in direction are called are called balanced balanced forces.forces. <http://www.geocities.com/>

What is the result of unbalanced What is the result of unbalanced forces?forces?

If both students push If both students push equally in opposite equally in opposite directions, the book directions, the book does not move.does not move.If the student on the If the student on the right pushes harder as right pushes harder as shown, movement will shown, movement will be to the left.be to the left.Net force is the sum of Net force is the sum of all forces acting on the all forces acting on the object.object.

Inertia and MassInertia and MassInertiaInertia is the tendency of an object to resist any is the tendency of an object to resist any change in its motion.change in its motion.

If it’s moving, it will keep moving until a force If it’s moving, it will keep moving until a force changes either its direction or speed.changes either its direction or speed.

A dirt bike will move in a straight line with a A dirt bike will move in a straight line with a constant speed until a force acts on it. A force constant speed until a force acts on it. A force can turn the wheel to change direction or friction can turn the wheel to change direction or friction can slow the speed.can slow the speed.

If it’s motionless, it still has inertia & will remain If it’s motionless, it still has inertia & will remain motionless until an unbalanced force causes it to motionless until an unbalanced force causes it to move.move.

<http://www.toledo-bend.com/>

Why can different objects have Why can different objects have different inertia?different inertia?

Inertia is related to Inertia is related to the mass of the the mass of the object.object.

Mass is the amount of Mass is the amount of matter in an object.matter in an object.

A bowling ball has A bowling ball has greater inertia than a greater inertia than a table tennis ball.table tennis ball.

<http://www.buckaball.com>

<http://www.solarnavigator.net/>

What are Newton’s laws of motion?What are Newton’s laws of motion?

British scientist, Sir Isaac Newton, stated rules British scientist, Sir Isaac Newton, stated rules that describe the effects of forces on the motion that describe the effects of forces on the motion of objects.of objects.

They apply to all objects in motion from billiard They apply to all objects in motion from billiard balls to planets.balls to planets.

<http://i3.photobucket.com/albums/y90/hillaryk/newton.jpg>

What is Newton’s First Law of What is Newton’s First Law of Motion?Motion?

An object moving at a constant velocity An object moving at a constant velocity keeps moving at that velocity unless an keeps moving at that velocity unless an unbalanced force acts on it.unbalanced force acts on it.

An object at rest remains at rest unless a An object at rest remains at rest unless a net force acts on it.net force acts on it.

Newton’s first law of motion is sometimes Newton’s first law of motion is sometimes called the law of inertia.called the law of inertia.

<http://farm3.static.flickr.com/>

What happens in a crash?What happens in a crash?The law of inertia The law of inertia explains what explains what happens in a car happens in a car crash. Passengers crash. Passengers who are not wearing who are not wearing a safety belt continue a safety belt continue to move at the to move at the original speed of the original speed of the car despite the car car despite the car coming to slamming coming to slamming halt.halt.

<http://img.autohome.com.>

<http://www.edmunds.com>

How do safety belts help?How do safety belts help?

A person wearing a safety belt is attached A person wearing a safety belt is attached to the car so they will slow down as the car to the car so they will slow down as the car slows down. slows down. The safety belt prevents the passenger The safety belt prevents the passenger from slamming into the dashboard, from slamming into the dashboard, windshield, or seat backs.windshield, or seat backs.It also helps prevent people from being It also helps prevent people from being thrown from the car. Half the people who thrown from the car. Half the people who die in crashes would survive if they wore die in crashes would survive if they wore safety belts.safety belts.

In a 30 m.p.h. collision an …In a 30 m.p.h. collision an unbelted 160 lb. Person can strike another passenger, crash through a windshield and/or slam into the vehicle’s interior with a 4,800 lb. force.                                                                

<http://fonzation.com>