Transcript Motion and Forces ppt.

Motion is the study of
how something moves.
It is all around us even
though we sometimes
cannot see it!
Motion occurs when an
object changes position.
Motion is relative
•A book at rest relative to the
table it lies on is moving at
about 30 km/s relative to the
sun.
•Motion is always described
relative to something else.
DISTANCE VERSUS
DISPLACEMENT
Distance and
displacement are not
the same things.
Displacement is the
distance and direction
of an object’s final
position from its initial
position.
Distance does not
involve direction.
DISTANCE
VERSUS
DISPLACEMENT
Displacement is a
vector value.
A vector is a
quantity that is
specified by both
a size and a
direction.
• Speed is the measure of how
fast an object is moving
• Speed is usually expressed
in meters/second or mph
(miles per hour)
• Average speed can be
calculated using this
formula:
Average speed = distance
time
Average Speed is
different from
instantaneous speed
(speed at any
second).
Velocity: Velocity is speed WITH DIRECTION!!!!!
The velocity of an
object can
change, even
though the speed
of the object
remains constant.
ACCELERATION – Change in
the speed or direction of
an object over time.
*A decrease in velocity is
negative acceleration
*An increase in velocity is
positive acceleration
ACCELERATION = change in velocity
time interval
OR more precisely,
ending velocity-initial velocity
time interval
Force is any push
or pull that is
exerted on an
object, and is a
vector value.
Force causes acceleration –
think of a hockey puck
being hit again after it is
already in motion.
To increase the acceleration
of an object, you must
increase the net force
acting on it!
Net force is directly
proportional to
acceleration.
F ~ a.
Forces can be balanced
or unbalanced.
If forces are balanced,
there is no net
acceleration.
Unbalanced forces
result in an
acceleration.
Pressure is the amount of
force per unit area.
P=F/A
It is measured in pascals
(Pa). 1 Pa = 1 N/m2
Acceleration also
depends upon
mass.
They are inversely
proportional.
a ~ 1/m.
Friction always acts in a
direction to oppose
motion.
The force of friction
between the surfaces
depends on the kinds
of material in contact
and how much the
surfaces are pressed
together.
There are three types
of friction:
1) Static friction – The
frictional force that
prevents two
surfaces in contact
from sliding past
each other
2) Sliding Friction – The
force that acts in the
opposite direction to
the motion of a
surface sliding on
another surface.
3) Rolling Friction –
Frictional force
resisting motion in
the direction of a
force. Rolling
friction is usually
less than sliding
friction.
Air Resistance is a
form of friction
between objects and
air molecules.
The amount of air
resistance on an
object depends on
the size, shape, and
speed of the object.
If the air resistance of a falling
object reaches a point to
where it equals the weight of
the object, the net force will
be zero and will no longer
accelerate.
This is called terminal velocity.
THIS DOES NOT MEAN THAT
THERE IS NO MOVEMENT!
A skydiver reaches a terminal
velocity of 150 – 200 km/h
on average.
At low speeds, air resistance
is often negligible, but at
high speeds, it can make a
big difference.
If there is no air
resistance and
gravity is the only
thing affecting a
falling object, it is
in free fall.
All falling objects
accelerate due to
gravity.
The value for the
acceleration due to
gravity is g = 9.8 m/s2 (10
m/s2)
For objects thrown upward,
the speed decreases
upward the same rate as
the speed increases
moving downward.
To determine the
distance an
object falls
during free fall
use
d = ½ gt2
With negligible air
resistance, all falling
objects can be
considered to be
falling freely.
The effects of air
resistance are less
noticeable with more
compact objects.
A projectile is an
object that has been
shot or thrown
through the air.
Projectiles near the
Earth always follow
a curved path.
They have both
horizontal and
vertical velocity,
which is what
results in the
curve.
Without gravity, a
projectile fired
upwards would follow
a straight-line path.
If air resistance is negligible, a projectile will
rise to its maximum height in the same
time it takes to fall from that height to the
ground because of gravity.
A ball thrown and a
ball dropped from
the same
distance will both
hit the ground at
the same time –
Why?
With significant air resistance,
the range of a projectile is
diminished and the path is not
a true parabola.
Gravity is a
property of
matter. If an
object has
mass and takes
up space, it has
a gravitational
attraction to
other objects.
Every object attracts
every other object
with a force that for
any two objects is
directly
proportional to the
mass of each
object.
The greater the
masses, the greater
the force of
attraction between
them.
The farther away the
objects are from
each other, the less
the force of
attraction between
them.
F = G m1m2
d2
G = universal gravitational
constant
G = 6.67 x 10-11 Nm2/kg2
Gravitation decreases
according to the
inverse-square law.
The force of gravity
weakens as the
distance squared.
Ex: If you were three
times farther from
the center of the
Earth as you are
now, your weight
would be 1/9 of what
it is now.
Einstein
theorized that
the mass of an
object distorts
space time.
This was his
explanation for
gravitational
influence.
Newton’s First Law
of Motion (Law of
Inertia) – every
object continues
at rest, or in
motion in a
straight line at
constant speed,
unless acted
upon by an
outside force.
Momentum = an object’s mass x its
velocity (speed with direction).
SO,
Momentum = mass x velocity OR
p=mv
A train has more momentum than a
tennis ball? Why
Law of conservation of Momentum
The total amount of momentum in a
system is conserved
What does that mean????????????
Newton’s 2nd
Law of Motion
states that
force equals
mass times
acceleration.
F=ma
Interacting things
exert forces on
each other.
Newton’s 3rd Law
of Motion When one
object exerts a
force on a
second object,
it will exert an
equal and
opposite force
on the first
object.
One force is called the
action force and the
other force is called
the reaction force.
Ex: letting air out of a
balloon, bird flying
through the air,
walking, & space
shuttle lifting off.