Download FORCES,FRICTION

FORCES
A FORCE IS A PUSH
OR A PULL
To describe a force
completely, you
must know its…
1.
2.
STRENGTH
DIRECTION
The sum of all of the forces acting
on an object is the NET FORCE.
80N
50N
100N
12N
20N
18N
12N
70N
NET FORCE = 70N
18N
NET FORCE = 18N
20N
GRAVITY is a force.
GRAVITY causes objects
elephants
to fall toward earth.
GRAVITY is a force that
causes all objects in the
universe to be attracted
to each other.
You exert a gravitational
force on the stars as they
exert a gravitational force
on you!
WEIGHT is a force
Weight is caused by the
force of gravity pulling on a
object because of its mass.
FRICTION IS A FORCE
FRICTION is a force that
OPPOSES MOTION between
objects in contact with each other.
The STRENGTH of a friction
force is determined by…
1. How hard the objects press together
...press hard – MORE friction
…press lightly – LESS friction
2. The type of surface
Rough surface - MORE friction
Smooth surface - LESS friction
The 4 Main types of friction are
STATIC
FRICTION
SLIDING
FRICTION
…exists before
things move
…exists when things
slide past each
other
…exists
when an
object rolls
ROLLING
FRICTION
…exists between
FLUID
FRICTION
an object and
a fluid
AIR RESISTANCE is a type
of FLUID FRICTION
Free fall exists when gravity is the only
force acting on an object
– we don’t get free fall on earth’s
atmosphere because of air resistance
TERMINAL VELOCITY is the speed an
object achieves when gravity is balanced
out by air resistance
INERTIA is the tendency of an
object to resist changes in motion
An object in motion will stay in motion…
An object at rest will stay at rest…
…Unless acted upon by
an UNBALANCED force
Ask her:
Oh wait, you can’t ask her…
…she wasn’t wearing a seatbelt
…if the unbalanced
force acting on you
isn’t the seatbelt, it
could be the
dashboard or the
windshield!
NEWTON’s LAWS of MOTION
Newton’s 1st Law of Motion
AKA The Law Of Inertia
An object at rest will remain at rest, and an
object in motion will maintain its motion,
unless acted upon by an unbalanced force.
Remember:
INERTIA is the tendency of an
object to maintain its motion.
Inertia is what makes us lean
“out of” the turn in a car
When the car turns to the
left we feel like we are
moving to the right, but
really – we are just
continuing in a straight line!
Newton’s 2nd Law of Motion
Force, Mass and Acceleration are related.
FORCE = MASS x ACCELERATION
Acceleration = Force / Mass
Mass = Force / Acceleration
NEWTON’s 3rd LAW of MOTION
…if one object exerts a force on another object,
then the second objects exerts an equal
and opposite force on the first object.
In simplified terms:
For every action force, there is an
equal and opposite reaction force.
Action Force – the first force
Reaction Force – the force that “reacts” to
the action force
Action / Reaction Forces
DO NOT
cancel each other out
because they act on different objects!
In order for you to walk…
…you push backward on the floor
…and the floor pushes forward on you
MOMENTUM is related to an object’s mass and velocity
MOMENTUM = MASS x VELOCITY
Law of Conservation of Momentum
The total momentum of any group of
objects remains the same (is conserved)
unless outside forces act on the objects.
It can get more
complicated –
but we don’t
have to get into
that now!
That’s why they
teach physics in
high school and
college!