Forces / Friction Study Guide
for
Science
Use for Mrs. Grom’s
8th. Grade Science class
WHAT IS A FORCE?
• A FORCE is a push or a
pull!
A PUSH
• A FORCE can set an
object into motion.
• There are 2 types of
forces –
BALANCED and
UNBALANCED
OR A PULL!
BALANCED FORCES
• These are forces that are
EQUAL
and in
OPPOSITE DIRECTIONS
• DO NOT cause an object
to go into motion
and
DO NOT cause an object
to STOP motion already
begun.
UNBALANCED FORCES!
• These forces are
NOT EQUAL
and
IN THE SAME DIRECTION
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• CAN CAUSE an object to
START or STOP
its motion
FRICTION
• A force which
OPPOSES motion!
• OFTEN slows
things down.
• THREE TYPES
– SLIDING
– ROLLING
– FLUID
SLIDING FRICTION
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• Occurs when
something or someone
SLIDES across a
surface.
• LUBRICANTS like
oil or grease HELP
reduce sliding friction.
• LUBRICANTS
change sliding friction
to rolling friction.
ROLLING FRICTION
• This friction involves the
use of WHEELS, BALL
BEARINGS, TIRES, etc.
• This friction tends to be
less than sliding friction.
(using wheels can make
work easier)
FLUID FRICTION!
• This type of friction involves
EITHER WATER or AIR!
• This type of friction opposes
motion MUCH LESS than
sliding friction does!
• LUBRICANTANTS are often
used to CHANGE sliding
friction into FLUID friction
because it is LESS
DAMAGING.
• This is the TENDENCY of
matter to RESIST CHANGE
in motion.
Inertia
• FOUND in places like –
- amusement park rides
- a car going around a curve
- a car hitting its breaks hard
•
The object WANTS to keep
going in the direction the
motion has started the object in
like when you go forward as
you hit the breaks.
Sir Isaac Newton
(Not really necessary to know this for test – just interesting facts!)
• Birth - December 25, 1642
• Death - March 20, 1727
• Place of Birth Woolsthorpe, England
Known for:
• Inventing, in part, the branch of
mathematics now known as calculus
• Formulating the three laws of motion,
which describe classical mechanics
• Proposing the theory of universal
gravitation, which explains that all
bodies are affected by the force called
gravity
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Newton’s 1st. Law of Motion
• STATES THAT –
- An object at REST
will REMAIN at rest
and an object in
MOTION will
REMAIN in MOTION
unless ACTED
UPON by an outside
force.
The book will stay on the
table until someone moves it!
The tractor will stay in
motion until the farmer hits
the brakes.
Newton’s 2nd. Law of Motion
• This law describes how
FORCE, ACCELERATION
and MASS are related.
Which would require a greater
force (in NEWTONS) to
accelerate?
• The formula for this is:
Force = Mass X Acceleration
or
OR
FORCE is measured in NEWTONS!
/www.aloha.com/~isaac/3laws/2mid.htm
Newton’s
rd
3 .
Law of Motion
• Newton’s THIRD law
states that forces occur in
PAIRS.
IN OTHER WORDS:
For EVERY action, there is
an EQUAL and
OPPOSITE reaction!
ACTION – Stan punches Fred!
REACTION – Fred’s head moves
sideways and he yells “OUCH!”
ACTION: The rocket engines “fire up”
www.aloha.com/~isaac/3laws/3mid.htm
REACTION: The rocket lifts up off
the launch pad and begins it’s journey
into outer space.
GRAVITY!
• Gravity causes objects to
ACCELERATE at a rate of 9.8 m/sec/sec
when they are close to the Earth’s
surface.
• GRAVITY is a force that exists between
ALL objects in the universe.
• Newton’s Law of Universal Gravitation
states that ALL OBJECTS in the
UNIVERSE attract each other by the
force of gravity.
• The size of the force of gravity depends
on TWO factors –
1.) the mass of the two objects
2.) the distance between them
WEIGHT AND MASS
• WEIGHT is the
measure of the PULL
of gravity on a given
object (mass)