Forces and MotionForces and Motion

MotionMotion

What do you think it means to be in What do you think it means to be in motion? How can we tell if something motion? How can we tell if something

is in motion?is in motion?

MotionMotion

Motion:Motion: a change in position, measured a change in position, measured by distance and time.  by distance and time. 

MotionMotion

• Determining if an object changes Determining if an object changes position requires a frame of reference.position requires a frame of reference.

The Earth is the most common frame of The Earth is the most common frame of referencereference

SpeedSpeed

Speed: Speed: the distance traveled by a moving the distance traveled by a moving object per unit of timeobject per unit of time

To calculate speed, use the equation To calculate speed, use the equation

Speed = distance / timeSpeed = distance / time

Speed only gives distance and time!Speed only gives distance and time!

Average SpeedAverage Speed

Average speed: Average speed: the speed of moving the speed of moving objects is not always constantobjects is not always constant

To calculate average speed you look at To calculate average speed you look at total time and distancetotal time and distance

Average speed = total distance / total time

Average SpeedAverage Speed

1. What is your average speed if you take 1. What is your average speed if you take 2h to jog 8 miles ?2h to jog 8 miles ?

Speed= distance/ time Speed= distance/ time 8m/2h= 4 mph8m/2h= 4 mph 2. What is the average speed of a car if it 2. What is the average speed of a car if it

travels 500 miles in 20 hours?travels 500 miles in 20 hours? Speed= distance/ time Speed= distance/ time

500m/20h = 25 mph500m/20h = 25 mph

VelocityVelocity

Velocity Velocity is speed in a given direction.is speed in a given direction.

Velocity gives Velocity gives distance, time, and the distance, time, and the direction of traveldirection of travel..

Velocity changes by Velocity changes by changing direction changing direction or or changing speedchanging speed!!

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Scientists have a special way Scientists have a special way to measure a to measure a changechange in in

velocity:velocity:

AccelerationAcceleration

Acceleration is a change in velocity.

AccelerationAcceleration

The change in velocity/the time it takes for The change in velocity/the time it takes for the change to occurthe change to occur

Acceleration = Acceleration =

(final velocity – initial velocity) (final velocity – initial velocity)

timetime

Velocity is measured in m/s and time in Velocity is measured in m/s and time in seconds.seconds.

Calculating AccelerationCalculating Acceleration

A roller coaster’s velocity at the top of the A roller coaster’s velocity at the top of the hill is 10 m/s(initial) Two seconds later its hill is 10 m/s(initial) Two seconds later its velocity is 26 m/s (final). What is the velocity is 26 m/s (final). What is the acceleration of a roller coaster?acceleration of a roller coaster?

Acceleration= Acceleration= final velocity- initial velocityfinal velocity- initial velocity

timetime

Accel= Accel= 26m/s -10m/s 26m/s -10m/s = = 1616 = 8 m/s/s = 8 m/s/s

22 22

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If you’re speeding up, you have If you’re speeding up, you have positive acceleration.positive acceleration.

If you’re slowing down, you have If you’re slowing down, you have negative acceleration.negative acceleration.

If you’re changing speed quickly, you If you’re changing speed quickly, you have high acceleration.have high acceleration.

If you’re changing speed slowly, you If you’re changing speed slowly, you have low acceleration.have low acceleration.

The Way Acceleration Works:

True or false?True or false?

1.1. If you slow down on your bicycle, you If you slow down on your bicycle, you accelerate.accelerate.

2.2. If you ride your bicycle at a constant If you ride your bicycle at a constant speed, you cannot accelerate.speed, you cannot accelerate.

3.3. Changing the speed and changing the Changing the speed and changing the direction of your bicycle are both direction of your bicycle are both examples of acceleration. examples of acceleration.

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Example:Example:

You’re driving along in You’re driving along in your car and suddenly your car and suddenly have to slam on your have to slam on your brakes for a red light. brakes for a red light. Negative or positive Negative or positive acceleration? High or acceleration? High or low acceleration?low acceleration?

High negative acceleration because you’re slowing down quickly.

MomentumMomentum

MomentumMomentum The measure of how difficult it is to stop The measure of how difficult it is to stop

a moving objecta moving object

p = mvp: momentum (kg ·m/s)m: mass (kg)v: velocity (m/s)m

p

v

Calculating MomentumCalculating Momentum

A 20,000 kg ship is traveling east at 20 A 20,000 kg ship is traveling east at 20 m/s. What is the momentum of the ship?m/s. What is the momentum of the ship?

P=mv P=mv 20,000 kg X 20 m/s = 20,000 kg X 20 m/s = 400,000 kg* m/s400,000 kg* m/s

Law of conservation of momentumLaw of conservation of momentum

According to the According to the law of conservationlaw of conservation of of momentum: the total momentum of momentum: the total momentum of objects that collide will be the same before objects that collide will be the same before and after the collision. and after the collision.

Momentum will Momentum will notnot be lost during the be lost during the collision.collision.

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Quick ReviewQuick Review

VelocityVelocity: speed of motion: speed of motion

AccelerationAcceleration: change in velocity: change in velocityMomentum The measure of

how difficult it is to stop a moving object

ForceForce

Force: Force: any push or pullany push or pull

Forces are measured in _____ Forces are measured in _____

A _____ is the combination of A _____ is the combination of all of the forces acting on an all of the forces acting on an object.object.

ForcesForces

ForceForce

Balanced ForcesBalanced Forces

forces acting on forces acting on an object that are an object that are opposite in opposite in direction and direction and equal in sizeequal in size

no change in no change in velocityvelocity

Balanced vs. Unbalanced Balanced vs. Unbalanced ForcesForces

Balanced forces will not cause a Balanced forces will not cause a change in the motion of an object; they change in the motion of an object; they have a net force of zero N.have a net force of zero N.

Examples of balanced forces are: Examples of balanced forces are: 1. ______, 2. _____, 3. _____ .1. ______, 2. _____, 3. _____ .

Balanced vs. Unbalanced forcesBalanced vs. Unbalanced forces

Unbalanced forces could be best Unbalanced forces could be best described as described as __________________________ .__________________________ .

Examples of unbalanced forces are Examples of unbalanced forces are ___________________________ .___________________________ .

Force DrawingForce Drawing

Create a drawing that shows an Create a drawing that shows an example of balanced forces. The example of balanced forces. The drawing should show the forces drawing should show the forces acting on the object and what acting on the object and what

happens to the object if the forces happens to the object if the forces become unbalanced.become unbalanced.

ForcesForces

ForcesForces

You and a younger brother or You and a younger brother or sister are at a neighborhood pool. sister are at a neighborhood pool. Your brother or sister asks why Your brother or sister asks why

there are signs that say “NO there are signs that say “NO RUNNING!” What would be your RUNNING!” What would be your

answer?answer?

ForcesForces

_____ , ______ , and ______ are _____ , ______ , and ______ are examples of common lubricants.examples of common lubricants.

Therefore, it is easier to slip when there is Therefore, it is easier to slip when there is water on the floor because the water acts water on the floor because the water acts as a ______ that lessens the friction as a ______ that lessens the friction between the bottom of your shoe and the between the bottom of your shoe and the floor.floor.

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Pushing pedals, pressing Pushing pedals, pressing brakes, and kicking soccer brakes, and kicking soccer balls are all examples of balls are all examples of

forcesforces..A force is anything thatA force is anything that changes the velocity changes the velocity

of an objectof an object..

But what’s a But what’s a change in velocitychange in velocity??

A change in velocity is A change in velocity is accelerationacceleration, so . . ., so . . .

A force is anything that gives an object A force is anything that gives an object accelerationacceleration..

FrictionFriction

_____ is a force that opposes motion _____ is a force that opposes motion between two surfaces that are in contact. between two surfaces that are in contact.

A _____ is a substance that lessens A _____ is a substance that lessens friction. friction.

FrictionFriction

FrictionFriction force that opposes motion between 2 surfacesforce that opposes motion between 2 surfaces depends on the:depends on the:

• types of surfacestypes of surfaces• force between the surfacesforce between the surfaces

A _____ is a substance A _____ is a substance

that lessens friction.that lessens friction.

FrictionFriction

There are four types of friction.There are four types of friction.

FrictionFriction

Four Types of FrictionFour Types of Friction Static FrictionStatic Friction – force that acts on objects that – force that acts on objects that

are not moving. (Couch Potato)are not moving. (Couch Potato) Sliding FrictionSliding Friction - force that opposes the - force that opposes the

direction of motion of an object as it slides over direction of motion of an object as it slides over a surface. (Ice skating or bobsledding)a surface. (Ice skating or bobsledding)

Rolling FrictionRolling Friction – friction force that acts on – friction force that acts on rolling objects. (Rollerblading)rolling objects. (Rollerblading)

Fluid FrictionFluid Friction – force that opposes the motion of – force that opposes the motion of an object through a fluid. (Planes flying or an object through a fluid. (Planes flying or submarines traveling)submarines traveling)

FrictionFriction

Write a story Write a story that describes that describes what a day in what a day in your life would your life would be like if there be like if there

was was no no frictionfriction..

GravityGravity

GravityGravity

Isaac Newton discovered the ______ Isaac Newton discovered the ______ ______ of Gravitation.______ of Gravitation.

Gravity Gravity acts on any objects with mass. acts on any objects with mass.

Example: You and your books, pencils, Example: You and your books, pencils, paper, etc.paper, etc.

Universal Law of GravitationUniversal Law of Gravitation

Mass and gravity have a directly Mass and gravity have a directly proportional relationship.proportional relationship.

The distance between the centers of The distance between the centers of masses of the two objects and gravity masses of the two objects and gravity have an inversely proportional have an inversely proportional relationship.relationship.

Differentiate between Mass and Differentiate between Mass and Weight.Weight.

Weight is dependent upon the Weight is dependent upon the acceleration due to gravity on a acceleration due to gravity on a particular planet.particular planet.

For instance: For instance: g g on earth is 9.8 m/s on earth is 9.8 m/s²²

The The larger larger the planet, the _____ the the planet, the _____ the gravitational force.gravitational force.