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Balanced and Unbalanced Forces

Balanced and Unbalanced Forces. Vocabulary Vocabulary Chart Vocabulary Chart Vocabulary Chart with Definitions Vocabulary Chart with Definitions

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Page 1: Balanced and Unbalanced Forces. Vocabulary  Vocabulary Chart Vocabulary Chart  Vocabulary Chart with Definitions Vocabulary Chart with Definitions

Balanced and Unbalanced Forces

Page 2: Balanced and Unbalanced Forces. Vocabulary  Vocabulary Chart Vocabulary Chart  Vocabulary Chart with Definitions Vocabulary Chart with Definitions

VocabularyVocabulary Chart

Vocabulary Chart with Definitions

Page 3: Balanced and Unbalanced Forces. Vocabulary  Vocabulary Chart Vocabulary Chart  Vocabulary Chart with Definitions Vocabulary Chart with Definitions

Isaac Newton Sir Isaac Newton was a great

scientist and mathematician. Isaac Newton was the first person

to hypothesize that the force that pulls an apple to the ground also pulls the moon toward Earth, keeping it in orbit.

He developed three laws of motion that we still know to be true today

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Newton’s Laws of MotionAn object in motion tends to stay

in motion and an object at rest tends to stay at rest unless acted upon by an unbalanced force.

Force equals mass times acceleration

(F = ma).For every action there is an equal

and opposite reaction.

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Force A force is a push or a pull. Force gives an object the energy to

move, stop moving, or change direction. When you write with a pen you exert a

force. When you peddle your bike, blow your nose, turn on a faucet, chew your gum, or swimming in a pool, you are exerting forces on other objects.

We would never be able to move without exerting forces on things.

                                           

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Newton’s First Law of Motion

An object at rest will remain at rest unless acted on by an unbalanced (unequal) force.

An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced (unequal) force.

This law is often called "the law of inertia".

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What is meant by unbalanced force?

If the forces on an object are equal and opposite, they are said to be balanced, and the object experiences no

change in motion. If they are not equal and opposite, then the forces are unbalanced and the motion of the

object changes.

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Some Examples from Real Life

Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

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Law of Inertia Inertia- the tendency of an

object to resist a change in motion.

This law is the same reason why you should always wear your seatbelt.

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InertiaNewton’s First Law says that objects do

not accelerate spontaneously, they need an outside force to move.

This property of matter, which causes objects to resist acceleration, has been named “inertia”.

Newton’s First Law is often called the Law of Inertia.

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Examples of the Law of Inertia

index card/penny example magician's trick of pulling a tablecloth out from

under dishes on a table. when riding a horse, the horse suddenly stops

and you fly over its head car turns left and you appear to slide to the

right football player running with the ball Inertia in action – video clip

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More Examples from Real LifeA powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them.

On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).

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If objects in motion tend to stay in motion, why don’t moving objects keep moving forever?

Things don’t keep moving forever because there’s almost always an unbalanced force

acting upon it.

A book sliding across a table slows down and stops because of the force of friction.

If you throw a ball upwards it will eventually slow down and fall because of the force of gravity.

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Friction Friction is a force that opposes motion.

Friction acts in a direction opposite to the objects direction in motion.

Without friction, the object would continue to move at a constant speed forever.

Example: sliding friction. This is when two surfaces slide one over the other. A snowboarder slides over the snow covered slopes using sliding friction every day.

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FrictionThe amount of friction depends on:

The condition (smoothness/roughness) of the surfaces

The normal force between the surfaces

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Gravity Newton was the first person to seriously

study gravity Gravity is a force that attracts all

objects toward each other. The force of gravity is measured in units

called Newtons (N).

• What is gravity?

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GravityThe strength of gravity between

two objects depends on two factors:

1. masses of the objects (If mass increases, force also increases)

2. distance between the objects (If distance increases, force decreases)

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Gravity

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GravityThe greater the mass, the greater the

forceThe greater the distance, the less the

forceAcceleration due to gravity = 9.8 m/s/s

or 9.8 m/s2

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Mass vs. WeightMass- is the amount of matter in

an objectWeight- is the force of gravity on

an object The greater the mass the greater

the force (weight)Weightlessness – free from the

effects of gravityMass vs. Weight

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How does Friction work? In today’s experiment, we will see just

how friction effect our movements in everyday life.

Teacher Notes

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Newton’s Second Law

Force equals mass times acceleration.

F = ma

Acceleration: a measurement of how quickly an object is changing speed.

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Newton’s Second Law• Force = Mass x Acceleration• Force is measured in NewtonsACCELERATION of GRAVITY(Earth) = 9.8 m/s2

• Weight (force) = mass x gravity (Earth)

Moon’s gravity is 1/6 of the Earth’sIf you weigh 420 Newtons on earth, what will you weigh on the Moon?

70 NewtonsIf your mass is 41.5Kg on Earth what is your mass on the Moon?

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Newton’s Second Law

• WEIGHT is a measure of the force of ________ on the mass of an object

• measured in __________

gravity

Newtons

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Newton’s Second Law

One rock weighs 5 Newtons.The other rock weighs 0.5 Newtons. How much more force will be required to accelerate the first rockat the same rate as thesecond rock?

Ten times as much

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What does F = ma say?F = ma basically means that the force of an

object comes from its mass and its acceleration.

Something very small (low mass) that’s changing speed very quickly

(high acceleration), like a bullet, can still have a great force.

Something very small changing speed very slowly will have a very

weak force.

Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.

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Working with Newton’s 2ndComplete the

graphing Newton’s second law activity sheet

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Newton’s Third Law

For every action there is an equal and opposite reaction.

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Newton’s 3rd LawFor every action there is an equal and

opposite reaction.

Book toearth

Table tobook

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What does this mean?

For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

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Think about it . . .What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force.

Why does it hurt so much when you stub your toe? When your toe exerts a force

on a rock, the rock exerts an equal force back on your toe. The harder you hit

your toe against it, the more force the rock exerts back on your toe (and the

more your toe hurts).

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Action: earth pulls on you

Reaction: you pull on earth

Action and Reaction on Different Masses

Consider you and the earth

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Action: tire pushes on roadReaction: road pushes on tire

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Action: rocket pushes on gases

Reaction: gases push on rocket

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Consider hitting a baseball with a bat. If we call the force applied to the ball by the bat the action force, identify the reaction force.

(a) the force applied to the bat by the hands

(b) the force applied to the bat by the ball

(c) the force the ball carries with it in flight

(d) the centrifugal force in the swing

(b) the force applied to the bat by the ball

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3rd Law of Motion Wrap UpVideo clip

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Net ForceHow can you tell if something is equal

and opposite? Calculate it’s net force!

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Fettuccine Lab The height shall be at least 5 cm, supporting the book 5 cm

above the table. All parts of the book should be at least 5 cm above the table.

Use all or part of the 20 pieces of fettuccine and all or part of the 1 m of masking tape. No additional tape or pasta may be used.

Tape must be used to secure the support structure. The structure must be one unit that can be picked up and moved

The structure must have a minimum of three points of support. Test the pasta structure by placing a piece of paper on the

structure first. Then a lightweight book is placed on the structure. The lightweight book is removed, and a medium weight book is placed on the structure. Last, a medium weight book is removed and a textbook is placed on the structure. To be successful, the structure must hold the item for ten seconds.

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Tug of WarToday we will compete against the other

science classes in a demonstration of Newton’s third law of motion. All classes will do great, but Mrs.

Crossman’s class WILL win

Summarize your experience during Tug of War

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Brief History of magnets Magnets have been known for

centuries.

The Chinese and Greeks knew about the “magical” properties of magnets.

They used the mineral “magnetite” to help in navigation, because it always pointed in the same direction.

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Magnetic ForcesMagnetic forces are produced by

magnetic poles.Every magnet has both a North and

South pole.Like poles repel, unlike poles attract.

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Magnetic Fields Magnetic fields transmit magnetic forces. Direction of the field is from N to S. Field is stronger where field lines are closer. Unit of magnetic field strength is the Tesla.

The older unit Gauss is sometimes used. Earth’s magnetic field strength is about 10-4 Tesla

or about 1 Gauss

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How Magnets AttractA magnet near an unmagnetized piece

of iron causes Attractive magnetic force on the iron

This causes the iron to become temporarily magnetized

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How big is the earths magnetic field? Earth’s magnetic field extends far into space.

We call this the “magnetosphere.” When magnetic particles (mainly from the

sun), called “solar wind”, strike the magnetosphere, we can see a phenomenon called the…

Aurora Borealis in the Northern Hemisphere. Aurora Australis in the Southern Hemisphere.

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How does a compass work? We use the Earth’s magnetic field to find

direction. The needle of the compass always points

toward the magnetic south pole.

YES! That is correct. We call this direction “North”. Remember!! Opposites Attract!

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Electric Currents & Magnetism Since moving charges create magnetic fields,

an electric current creates a magnetic field. A coil of wire can concentrate the magnetic

field and create an electromagnet.

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MotorsAn electric motor uses a magnet to

exert a force on a current-carrying coil of wire.

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Review Magnet and Iron Fillings Demonstration

Truth About Magnets p.1

Truth About Magnets p.2

Answers

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ReviewNewton’s First Law:

Objects in motion tend to stay in motion and objects at rest tend to stay at rest unless acted upon by an unbalanced force.

Newton’s Second Law:

Force equals mass times acceleration (F = ma).

Newton’s Third Law:

For every action there is an equal and opposite reaction.

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1stlaw: Homer is large and has much mass, therefore he has much inertia. Friction and gravity oppose his motion.

2nd law: Homer’s mass x 9.8 m/s/s equals his weight, which is a force.

3rd law: Homer pushes against the ground and it pushes back.

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Bill Nye Force and Motion Video

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JeopardyWe will review for the test by playing a

game of Jeopardy!

Force and Motion Jeopardy

Forces Jeopardy