balanced and unbalanced forces. vocabulary vocabulary chart vocabulary chart vocabulary chart with...
TRANSCRIPT
Balanced and Unbalanced Forces
VocabularyVocabulary Chart
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
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.
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.
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".
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.
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.
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.
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.
Inertia at WorkCar crash with and without seatbelts an
d air bags
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
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).
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.
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.
FrictionThe amount of friction depends on:
The condition (smoothness/roughness) of the surfaces
The normal force between the surfaces
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?
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)
Gravity
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
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
Newton’s 1st Law activitieshttp://science360.gov/obj/video/70fadaa
8-c3d4-4132-ba1f-c98be5caeb14/science-nfl-football-newtons-first-law-motion
Wacky washers and penny lab
How does Friction work? In today’s experiment, we will see just
how friction effect our movements in everyday life.
Teacher Notes
Newton’s Second Law
Force equals mass times acceleration.
F = ma
Acceleration: a measurement of how quickly an object is changing speed.
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?
Newton’s Second Law
• WEIGHT is a measure of the force of ________ on the mass of an object
• measured in __________
gravity
Newtons
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
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.
Working with Newton’s 2ndComplete the
graphing Newton’s second law activity sheet
Newton’s Third Law
For every action there is an equal and opposite reaction.
Newton’s 3rd LawFor every action there is an equal and
opposite reaction.
Book toearth
Table tobook
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.
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).
Action: earth pulls on you
Reaction: you pull on earth
Action and Reaction on Different Masses
Consider you and the earth
Action: tire pushes on roadReaction: road pushes on tire
Action: rocket pushes on gases
Reaction: gases push on rocket
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
3rd Law of Motion Wrap UpVideo clip
Net ForceHow can you tell if something is equal
and opposite? Calculate it’s net force!
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.
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
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.
Magnetic ForcesMagnetic forces are produced by
magnetic poles.Every magnet has both a North and
South pole.Like poles repel, unlike poles attract.
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
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
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.
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!
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.
MotorsAn electric motor uses a magnet to
exert a force on a current-carrying coil of wire.
Review Magnet and Iron Fillings Demonstration
Truth About Magnets p.1
Truth About Magnets p.2
Answers
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.
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.
Bill Nye Force and Motion Video
JeopardyWe will review for the test by playing a
game of Jeopardy!
Force and Motion Jeopardy
Forces Jeopardy