Introduction to Introduction to Forces: Forces:

Common MisconceptionsCommon Misconceptions

Common Misconceptions about ForcesCommon Misconceptions about Forces

True or FalseTrue or False

____ When a ball has been thrown, the ____ When a ball has been thrown, the force of the hand that threw it force of the hand that threw it remains on itremains on it

____ A force is needed to keep an ____ A force is needed to keep an object movingobject moving

____ Inertia is a force____ Inertia is a force

____ Air does not exert a force____ Air does not exert a force

____ The quantity ____ The quantity mama is a force is a force

Common Misconceptions about ForcesCommon Misconceptions about Forces

Short AnswerShort AnswerIf there is no net force the object will continue If there is no net force the object will continue

with ________ velocity with ________ velocity (unchanged, increased, (unchanged, increased, or decreased)or decreased)

Inertia is the tendency of an object to resist Inertia is the tendency of an object to resist ____________________. ____________________. (motion, change in (motion, change in motion, increase in motion, or decrease in motion, increase in motion, or decrease in motion)motion)

The force exerted by air is a ____________ force. The force exerted by air is a ____________ force. (small, balanced, or negative)(small, balanced, or negative)

The equation F= _____ is a mathematical model The equation F= _____ is a mathematical model of Newton’s 2nd Law.of Newton’s 2nd Law.

Newton’s First Law Newton’s First Law of Motion of Motion

( The Law of Inertia)( The Law of Inertia)

Homework:Homework:

Read 4.1-4.3 and be prepared for a brief quiz Read 4.1-4.3 and be prepared for a brief quiz tomorrowtomorrow

Aristotle and the Early Greeks Aristotle and the Early Greeks (Around 300 B.C.)(Around 300 B.C.)

► Believed there were Believed there were two types of motion two types of motion and they were:and they were:

Natural motionNatural motion – objects were moving – objects were moving because they were moving toward because they were moving toward their their natural resting placenatural resting place

Violent motionViolent motion – imposed motion. This – imposed motion. This was the result of an object being was the result of an object being pushed or pulled.pushed or pulled.

A More Modern View: A More Modern View: Galileo Galilei (1564-1642)Galileo Galilei (1564-1642)

► Used his telescope to make such Used his telescope to make such astronomical discoveries such as astronomical discoveries such as the rough surface of the moon, the the rough surface of the moon, the four moons revolving around four moons revolving around Jupiter, “sunspots”, the fact that Jupiter, “sunspots”, the fact that the Milky Way is made up of a the Milky Way is made up of a myriad of single, far-away stars and myriad of single, far-away stars and the phases of Venus.the phases of Venus.

► Used the Leaning Tower of Pisa as Used the Leaning Tower of Pisa as a laboratory to test his law of falling a laboratory to test his law of falling bodies.bodies.

► Was the first “scientist” because he Was the first “scientist” because he used experiments to used experiments to prove/disprove his ideas.prove/disprove his ideas.

Galileo and His Ramp ExperimentGalileo and His Ramp Experiment

► Galileo did an experiment with two Galileo did an experiment with two ramps. The ball rolls down the incline ramps. The ball rolls down the incline and up the opposite incline and reaches and up the opposite incline and reaches almostalmost its initial height. its initial height.

► He replaced the second ramp with a He replaced the second ramp with a longer, less-steep ramp and released longer, less-steep ramp and released the ball on the first ramp. The ball the ball on the first ramp. The ball rolled further and up the second incline rolled further and up the second incline to to almost almost the same height from where it the same height from where it was released.was released.

► Hypothetically Galileo reasoned that if Hypothetically Galileo reasoned that if the second ramp was removed the second ramp was removed altogether, the ball would roll down the altogether, the ball would roll down the first incline plane and roll forever and first incline plane and roll forever and ever trying to attain the same height ever trying to attain the same height from where it was released.from where it was released.

Comparison between Aristotle and Comparison between Aristotle and GalileoGalileo

ARISTOTLEARISTOTLE► Things at rest were Things at rest were

at their natural at their natural resting place.resting place.

►Objects that are Objects that are moving away from moving away from their natural resting their natural resting place need to be place need to be continuously forced continuously forced to keep them to keep them movingmoving

GALILEOGALILEO►Objects at rest stay Objects at rest stay

at rest until at rest until something forces something forces them to do them to do otherwise.otherwise.

►Objects in motion Objects in motion want to continue in want to continue in motion unless motion unless something stops something stops them.them.

InertiaInertia

► Idea that Galileo Idea that Galileo came up withcame up with

►Derived from Latin Derived from Latin meaning “idleness” meaning “idleness” or “laziness”or “laziness”

►Definition: an Definition: an objects’ resistance objects’ resistance to change its state to change its state of motionof motion

Sir Isaac NewtonSir Isaac Newton

► Born on Christmas Born on Christmas Day in 1642Day in 1642

► Please see thumbnail Please see thumbnail sketch of his lifesketch of his life

► ““If I have been able If I have been able to see further, it was to see further, it was only because I stood only because I stood on the shoulders of on the shoulders of giants.”giants.”

Newtons 1Newtons 1stst Law of Motion Law of Motion (The Law of Inertia)(The Law of Inertia)

►Every object continues in a state of Every object continues in a state of rest, or of motion in a straight line at rest, or of motion in a straight line at constant speed, unless it is compelled constant speed, unless it is compelled to change that state by forces exerted to change that state by forces exerted upon it.upon it.

► In other words:In other words: Objects at rest, stay at restObjects at rest, stay at rest Objects in motion, stay in motion.Objects in motion, stay in motion. UNLESS ACTED UPON BY AN OUTSIDE UNLESS ACTED UPON BY AN OUTSIDE

FORCEFORCE

Vocabulary termsVocabulary terms

►InertiaInertia – Tendency of an object to – Tendency of an object to resist change in motionresist change in motion

►EquilibriumEquilibrium – an object is in – an object is in equilibrium if it is at rest or moving with equilibrium if it is at rest or moving with a constant velocity (note: rest is a a constant velocity (note: rest is a constant velocity of zero). (For this to constant velocity of zero). (For this to be achieved the NET force has to be be achieved the NET force has to be zero, more about this later)zero, more about this later)

Vocabulary Terms continuedVocabulary Terms continued

►contact forcescontact forces – push or pull on an – push or pull on an object through touching it (contact)object through touching it (contact)

►Long rangeLong range – push or pull on an – push or pull on an object without direct contactobject without direct contact

►AgentsAgents – cause of force (i.e. – cause of force (i.e. “applied”, gravity, “normal”, friction, “applied”, gravity, “normal”, friction, … among others)… among others)

What gives an object a lot of What gives an object a lot of Inertia?Inertia?

► Is it volume?Is it volume?

Volume – the amount Volume – the amount of space an object of space an object takes uptakes up

NO!!!!!!NO!!!!!!

What gives an object a lot of What gives an object a lot of Inertia?Inertia?

► Is it weight?Is it weight?

Weight – the effect Weight – the effect that gravity has on that gravity has on an objectan object

NO!!!!!!NO!!!!!!

What gives an object a lot of What gives an object a lot of Inertia?Inertia?

► Is it mass?Is it mass?

Mass – the amount of Mass – the amount of matter an object matter an object possesses.possesses.

-the amount of -the amount of “stuff” something “stuff” something hashas

YES!!!!!!!!!!!!!!!!!YES!!!!!!!!!!!!!!!!!

Can you measure mass in Can you measure mass in space?space?

Yes. Since astronauts Yes. Since astronauts are weightless during are weightless during their mission, their mission, keeping track of their keeping track of their weight can not be weight can not be accomplished by accomplished by asking them to step asking them to step on the traditional on the traditional bathroom scale. bathroom scale. They are strapped They are strapped into a device called into a device called an inertial balance an inertial balance and vibrated back and vibrated back and forth. What and forth. What would happen to the would happen to the period of vibration if period of vibration if the astronaut losses the astronaut losses mass? How about if mass? How about if he/she gains mass?he/she gains mass?

ConcussionsConcussions

► A concussion occurs A concussion occurs when the brain collides when the brain collides with the skull and the with the skull and the result is bruising of the result is bruising of the brain. Sometimes the brain. Sometimes the person loses person loses consciousness. New consciousness. New technology in the technology in the design of helmets helps design of helmets helps to reduce the chance of to reduce the chance of a concussion occurringa concussion occurring

WhiplashWhiplash

► Whiplash is the term Whiplash is the term that is used when that is used when someone is struck someone is struck from behind, either from behind, either in a car, or not and in a car, or not and the head stays at the head stays at rest while the body rest while the body moves forward moves forward causing the head to causing the head to make a whipping make a whipping motion.motion.

Homework AssignmentHomework Assignment

►Due tomorrow, you are to find a Due tomorrow, you are to find a specific example of Newton’s 1specific example of Newton’s 1stst Law. Law. Your example should… Your example should… be written in your notebookbe written in your notebook include diagramsinclude diagrams be unique.be unique.

Any duplications will receive a zero (0). Any duplications will receive a zero (0). Any examples discussed in class may not Any examples discussed in class may not be used.be used.

How do you change the state of How do you change the state of motion of an object?motion of an object?

Apply a Force!Apply a Force!

Force- a push or a pullForce- a push or a pull

-measured in Newtons (N)-measured in Newtons (N)

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