Getting an Getting an AA in Science in Science

Taking Taking ownership or controlownership or control of the information of the information learned in class and taking learned in class and taking responsibilityresponsibility for for your workyour work This means:This means:

• Practicing (reviewing, restating, preparing)Practicing (reviewing, restating, preparing)

• Applying (creating, thinking, using)Applying (creating, thinking, using)

• Planning (studying, completing projects and homework, Planning (studying, completing projects and homework, being prepared-pencils, books)being prepared-pencils, books)

Intro to PhysicsIntro to Physics

What is physics?What is physics? https://www.youtube.com/watch?v=2vYI2NcVsXY https://www.youtube.com/watch?v=Nd4PlvzMsaQ

Motion & ForcesMotion & ForcesChapter 2 Chapter 2

MotionMotion What does motion mean?What does motion mean?

How can we tell if something is in motion? How can we tell if something is in motion? Is this marble in motion? Is this marble in motion?

How do you know? How do you know? How can we provide evidence?How can we provide evidence?

MotionMotion

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

Frame of Reference Frame of Reference

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

• Frame of reference is the object or point from Frame of reference is the object or point from which movement is determined which movement is determined

What is the frame of reference for this video? How

do I know the skater is in

motion?

Frame of Reference Frame of Reference

Movement is relative to an object that Movement is relative to an object that appearsappears stationary stationary

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

Motion of the MarbleMotion of the Marble We can tell if the marble is in motion by We can tell if the marble is in motion by

measuring its change in position along the measuring its change in position along the ruler (our frame of reference). ruler (our frame of reference).

Right now, the marble is NOT in motion. It Right now, the marble is NOT in motion. It is not changing position. How can we get is not changing position. How can we get it to change position?it to change position?

How to make things moveHow to make things move

https://www.youtube.com/watch?v=LEs9J2IQIZY

ForceForce A force is a push or a pullA force is a push or a pull Forces can affect motionForces can affect motion in in

several ways.several ways. Forces can make objects:Forces can make objects:

• Start movingStart moving• Move fasterMove faster• Move slowerMove slower• Stop movingStop moving• Change directionChange direction• Change shapeChange shape

What forces are at work…What forces are at work…

During a rocket launch?During a rocket launch? Upwards force (thrust) from Upwards force (thrust) from

enginesengines Downwards force from Downwards force from

gravitygravity Downwards force (drag) Downwards force (drag)

from air resistancefrom air resistance

What forces are at work…What forces are at work…

pushing a truck?pushing a truck? Forwards force Forwards force

from pushingfrom pushing Backwards force Backwards force

from frictionfrom friction Downwards force Downwards force

from gravityfrom gravity Upwards force Upwards force

from ground.from ground.

What forces are at work…What forces are at work…Kicking a football?Kicking a football?

Upwards force from kickUpwards force from kickDownwards force from gravityDownwards force from gravityBackwards force from air frictionBackwards force from air friction

Fkick

Fgrav

Fair

FrictionFriction FrictionFriction

force that opposes motion between 2 surfacesforce that opposes motion between 2 surfaces

It depends on the:It depends on the:• types of surfacestypes of surfaces

• force between the surfacesforce between the surfaces

FrictionFriction

Friction is greater...Friction is greater... between rough surfacesbetween rough surfaces when there’s a greater force between the when there’s a greater force between the

surfaces (e.g. more weight)surfaces (e.g. more weight)

How strong is the force?How strong is the force? Forces are measured in NewtonsForces are measured in Newtons

https://www.youtube.com/watch?v=PCxP24qj2UQ

Wrong kind of force…Wrong kind of force…

Measuring Forces that cause Measuring Forces that cause motionmotion

Units are Newtons Units are Newtons (N)(N)

Forces are Forces are measured using a measured using a springspring scalescale or or forceforce metermeter..

https://www.youtube.com/watch?v=AFu1advEnhw

Forces occur in pairsForces occur in pairs

The force pairs can be balanced or The force pairs can be balanced or unbalancedunbalanced

Balanced ForcesBalanced Forces

Balanced forces Balanced forces cause NO change cause NO change in motionin motion

Balanced forces Balanced forces are equal in size are equal in size and opposite in and opposite in directiondirection

Balance forces = no motionBalance forces = no motion

Unbalanced ForcesUnbalanced Forces

Unbalanced forces always cause a Unbalanced forces always cause a change in motion, speed, or directionchange in motion, speed, or direction

Which way will the boy in the middle be Which way will the boy in the middle be pulled?pulled?

Unbalanced ForcesCauses Motion

Adding Forces Subtracting Forces

Unbalanced ForcesCauses motion

Adding Forces

5 NObject

5 N

Notice that all the forces are pointed in the same direction. Hence they add together.

Subtracting Forces

• Two forces can subtract to produce a net force in the direction of the larger force.– Negative motion occurs (Slow Down)

10 N 5 N= 5 N

Unbalanced ForcesCauses Motion

Subtracting Forces

5 N5 NObject

5 N

Notice that all the forces are unequal and pointed in the opposite direction. Hence they

are unbalanced and in opposition to each other – or one partially cancels the other.

Which game will result in a Which game will result in a winning team? winning team?

How do you know?How do you know?

Balanced Forces

Balanced

Push

i.e. Pushing a Car

No motion

Balanced

Pull

i.e. Tug-of-war

No motion

10N10N

10N10N

Un-Balanced Forces

Additive Un-Balanced

Same Direction

i.e. sled

Faster

motion

Subtractive Un-Balanced

Opposite Direction

i.e. football tackle

Slower

motion

10N10N

10N10N

10N

Why do I care?Why do I care?• Understanding an object’s motion can help

you understand how to interact with the world around you.

Review of balanced and Review of balanced and unbalanced forcesunbalanced forces

https://www.youtube.com/watch?v=HEJOybRxclk

Stop hereStop here

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.

GravityGravity

GravityGravity force of attraction between any two force of attraction between any two

objects in the universeobjects in the universe

increases as...increases as...

• mass increasesmass increases

• distance decreasesdistance decreases

GravityGravity

Who experiences more gravity - the astronaut or Who experiences more gravity - the astronaut or the politician?the politician?

less distance

more mass

Which exerts more gravity - Which exerts more gravity -

the Earth or the moon?the Earth or the moon?

GravityGravity Would you weigh more on Earth or Would you weigh more on Earth or

Jupiter?Jupiter?

greater gravitygreater gravity

greater weightgreater weight

greater massgreater mass

Jupiter because...Jupiter because...

Gravity pulls down on you…

The ground pushes back up…

THIS KEEPS YOU WHERE YOU ARE!If these football players push on each other equally as hard,

will either one move?

Gravity pulls down

Ground pushes up

Balanced Forces (Balanced Forces = No Motion)

Newton’s First LawNewton’s First Law Newton’s First Law of MotionNewton’s First Law of Motion

An object at rest will remain at An object at rest will remain at rest and an object in motion rest and an object in motion will continue moving at a will continue moving at a constant velocity unless acted constant velocity unless acted upon by a net or unbalanced upon by a net or unbalanced forceforce..

Two Key PointsTwo Key Points

Newton’s First LawNewton’s First Law Newton’s First Law of MotionNewton’s First Law of Motion

““Law of Inertia”Law of Inertia”

InertiaInertia tendency of an object to resist any change tendency of an object to resist any change

in its motionin its motion increases as increases as massmass increases increases

Can you explain how this trick works, using newton’s first law of motion?

Newton’s Second LawNewton’s Second Law

Newton’s Second Law of MotionNewton’s Second Law of Motion The acceleration of an object is The acceleration of an object is directly proportionaldirectly proportional

to the net force acting on it and to the net force acting on it and inversely inversely proportionalproportional to its mass. to its mass.

F = ma

Newton’s Second LawNewton’s Second Law

F = maF: force (N)m: mass (kg)a: accel (m/s2)

1 N = 1 kg ·m/s2

am

F

a

Fm

CalculationsCalculations What force would be required to accelerate a 40 What force would be required to accelerate a 40

kg mass by 4 m/skg mass by 4 m/s22??

GIVEN:

F = ?

m = 40 kg

a = 4 m/s2

WORK:

F = ma

F = (40 kg)(4 m/s2)

F = 160 N

m

F

a

CalculationsCalculations A 4.0 kg shotput is thrown with 30 N of force. A 4.0 kg shotput is thrown with 30 N of force.

What is its acceleration?What is its acceleration?

GIVEN:

m = 4.0 kg

F = 30 N

a = ?

WORK:

a = F ÷ m

a = (30 N) ÷ (4.0 kg)

a = 7.5 m/s2

m

F

a

ConcepTestConcepTest

Is the following statement true or false?Is the following statement true or false? An astronaut has less mass on the moon An astronaut has less mass on the moon

since the moon exerts a weaker gravitational since the moon exerts a weaker gravitational force.force.

False! Mass does not depend on gravity, weight False! Mass does not depend on gravity, weight does. The astronaut has less does. The astronaut has less weightweight on the on the moon.moon.

Newton’s Third LawNewton’s Third Law

Newton’s Third Law of MotionNewton’s Third Law of Motion When one object exerts a force on a When one object exerts a force on a

second object, the second object exerts second object, the second object exerts an equal but opposite force on the first.an equal but opposite force on the first.

Newton’s Third LawNewton’s Third Law

Action-Reaction PairsAction-Reaction Pairs

The hammer exerts a The hammer exerts a force on the nail to the force on the nail to the right.right.

The nail exerts an equal The nail exerts an equal but opposite force on but opposite force on the hammer to the left.the hammer to the left.

Newton’s Third LawNewton’s Third Law

Action-Reaction PairsAction-Reaction Pairs The rocket exerts a The rocket exerts a

downward force on the downward force on the exhaust gases.exhaust gases.

The gases exert an equal The gases exert an equal but opposite upward force but opposite upward force on the rocket.on the rocket.

FG

FR

Newton’s Third LawNewton’s Third Law

Action-Reaction PairsAction-Reaction Pairs

Both objects accelerate.Both objects accelerate. The amount of acceleration depends on the The amount of acceleration depends on the

mass of the object and the force applied.mass of the object and the force applied. Force = mass x acceleration F=maForce = mass x acceleration F=ma

Small mass Small mass more acceleration more acceleration Large mass Large mass less acceleration less acceleration