Transcript NEWTON`S THREE LAWS OF MOTION

NEWTON’S THREE LAWS OF
MOTION
I. An object will remain at rest or will continue to move
uniformly in a straight line at a constant velocity (speed
and direction) unless acted upon by a force.
Inertia example pushing a stationary object on a table
2. The rate of change of velocity of an object is proportional
to the force acting on it
(more input energy to an object = more velocity
Acceleration example stepping harder on a gas peddle
3. If one object exerts a force eon another, that second
object exerts an equal and opposite force on the first
Action, Reaction
Energy in Motion related to 1st Law
• Projectile motion
-a thrown object into the air and the path that it
follows
1. downward = gravity force
2. forward = inertia force–an object will remain
in its present state of rest or motion if no other
force is introduced to it to cause a change
(wants to keep doing whatever it is doing at the
present time).
-the motion always resembles a curved path
-gravity force is always stronger than
inertia and the object is eventually pulled
to the ground.
-example –a thrown ball
• Orbital motion
-a path around an object is an orbit
-an object following this path is in orbital
motion
-if an object’s forward force is inertia (its
present speed) = the force of gravity
(downward), then the forces are
balanced and the object follows an orbital
path.
-vertical force acting on the object is
gravity
– horizontal force acting on the object is inertia
(speed of the object)
–
+
=
-example -space shuttle
The gravity force = the speed of inertia so it stays in
orbit
-considered to be in freefall around the earth
-anyone inside has a weightless experience
-if either force is increased or decreased
-increased gravity = falls to the ground
-increased inertia (speed) = escape
velocity –can escape from its orbit
Newton's Universal Gravitational
Law
• All objects are attracted to each other by the
force of gravity
• Magnitude of the force depends on
1. the mass of the object
2. the distance between objects
*increased mass = increased effect of the force of
gravity on the object (takes more effort to pull
down a larger object)
*distance increases between objects = decrease in
the effect of the force of gravity on the object
Weight
• Weight = mass x acceleration force of
gravity
Mass
M
Kg
gravity
g
9.8 m/s2
m x g = A Newton
mg = N
• Smaller mass = smaller gravitational force
acting on the object
• Increased distance (farther apart) =
smaller gravitational force acting on the
objects
• Farther from the center of the earth (where
gravity is thought to come from) --liquid
core/plates moving– means smaller
gravitational force acting on the object
• At sea level = greater gravitational effect on an object
• On a mountain = less of a gravitational effect on an
object
• On the moon = much less of an effect of earth’s
gravitational effect
you seem weightless because you only have mass
(m) not (mg)
-g (gravity from the earth) is missing. Too far from
the center of the earth for it to affect you. Plus you
have a small mass compared to the moon and the
earth.
• Near the earth, the acceleration due to
gravity is 9.8 m/s2
• For every second an object falls, its
velocity increases 9.8 m/s every second
• 1sec
2sec
3sec
9.8m/s
19.6m/s
29.4m/s
+9.8
+9.8
Fluid Motion Energy
Viscosity
-the ease of difficulty to flow
-thin and nonsticky -water = easy to flow
-thick and sticky –syrup = difficult to flow
-friction force reduces the ease to flow
-high viscosity = greater resistance to flow
turbulent flow
-low viscosity = not so much resistance to flow
streamline flow
Fluid flow
-the ease by which a fluid flows depending on its thickness and
stickiness
-fluid is described as air, a gas, or a liquid
example
air flow
-a car moving through air –aerodynamics
gas flow
-taking the top off a pop can -diffusion
liquid flow
-pouring a liquid into a glass
-measured in a substance’s internal friction which creates a
resistance to flow
Ouch!
Example
-raindrops in the atmosphere inside friction
slows them down. This friction inside cancels
out the acceleration due to gravity
If it didn’t, raindrops would hit the ground and
your head at 150 m/s
Example
-water pipe –faucet
-increase the pressure = turbulent flow
-decrease the pressure = streamline flow
Air resistance
•
•
•
•
Is a force that affects free falling objects
A feather is more affected than a boulder
Paper is more affected than a rock
As an object falls, if the air resistance
equals the pull down of gravity, the object
appears to float. If there is no more
acceleration of the object because the pull
down = the upward force, the object is said
to have terminal velocity
FREE FALL ACCELERATION
• All objects accelerate at
the same rate towards
the ground regardless of
their masses
• A boulder and a pebble
were thrown off of the
Empire State building. If
there were no other
forces acting on them,
they would hit the ground
at the same time but with
different forces
• The rate of the fall is the
acceleration rate of
gravity
• The gravity force acting
between an object and
the earth causes this
acceleration of falling
objects headed towards
the earth
Harmonic Motion Energy
Harmonic motion related to 1st Law
-a small to-and-fro movement that occurs
whenever an apparent stationary object is
slightly disturbed -pushed example pendulum
-measured by lengths of the pendulum, the
force of gravity, time of a full swing, and
constants
Tries to keep going -Inertia but stops –gravity
force
Pendulum Lab formula (get ready for this)
Check out length and weight of a
pendulum to see if it affects the
time of its swing
Pendulum formula
T2 = 4 x 9.86 (L/G) so
T2 = 39.44 x (L/9.8)
G = 9.8m/s2
T = time of a full to and fro swing
measure with stop watch while counting and divide by how many times it
swung a full back and forth movement
L = length of the string
measure with a ruler in meters
PI = 3.14, squared = 9.86
So let’s try to prove that gravity is 9.8m/s2
G = T2 divided by 39.44 times the length of the string
G = T2/39.44xL
ENERGY IN MOTION
related to 2nd Law
• Speed
distance traveled
time it took to travel
that distance
*distance / time = speed
Meters / seconds
Miles / hours
• Acceleration
to move with constant
increasing speed
could be positive or
negative acceleration
*speeding up = positive
*slowing down = negative
Force of Friction causes
objects to slow down
Forces that affect a Moving cart
If the cart is moving, it wants to keep moving
Gravity force
Friction force
Force of Inertia
Force of the Pavement
FORCE = mass x acceleration
• There needs to be a
applied strong enough to
start an object rolling
push or pull
• It must be an
unbalanced force
(stronger to overcome
what the object is
currently doing)
• Heavier things require
more effort to start them
rolling
• Mass x acceleration
kg
x m/s/s
m
x a = the force
that produces movement
*Force is measured in
Newtons
Energy in Motion related to 3rd Law
Example of action, reaction
-pool ball collision
Mass x velocity = mass x velocity
-helicopter –downward force of air
equal and opposite reaction =
lift off
-you sitting in a chair –downward force pulling you onto
to the chair and opposite reaction = chair pushing up on
you
• Relativity of motion
– 1. relating one object’s motion to another
object’s motion
– A car moves relative to the earth’s motion
-rotate, revolve
– Example
Earth
• Example
• A + B = relative velocity
• ______A__________________________ - - - - - - - -- - - - - - - - -- - • ________________B________________
A car moving parallel to another in the same
direction
They are moving relative to each other in a parallel
direction
Their velocity (speed) determines their relative
velocity to each other
• A –B = Relative velocity
_______A___________________________
- - - - - - - - - - - - - - - - - - - - - ____________________B______________
Comparison of A’s relative velocity to B’s
relative velocity going in opposite
directions
B – A = relative velocity