Transcript Motion Unit Notes

Motion Notes
Measurement
• A measurement is a quantity with a unit that
tells what time the quantity means.
• For example:
– 3 seconds is a measurement of time that
includes a quantity ( 3 ) and a unit (seconds).
– A quantity is a number.
– A unit is a
Units for Motion
• Length (Distance)
– Milimeters
– Meters
– Kilimeters
• Time
– Seconds
– Minutes
– hours
MOTION
• Motion change in your position
compared to a frame of
reference.
– as a train moves past a platform, people
on the platform see those on the train
speeding by. when people on the train look
at one another, they don't seem to be
moving at all OR moving backwards
MOTION
• frame of reference comparing an object’s
motion to another object
–Your house stays still as the
cars drive past
–a frame of reference is
necessary in order to describe
motion
• Speed distance traveled per
unit of time
– S = d/t
–A car travels 70 km per hour
–Choose units that make sense:
m/s, km/h
Formulas
S
D
T
MOTION
• Distance the length of a
path between two points.
–GO METRIC: km, m, mm, cm,
etc.
Time
• the measured or measurable period during
which an action, process, or condition exists
or continues : duration.
• Average speed- the total
distance traveled, d, divided
by the total time, t, it takes to
travel that distance.
speed= distance/time
• Ex- on vacation: 60 km in 0.8 hr, and
35 km in 0.5 hr. What is your
average speed?
• Instantaneous speed the rate
at which an object is moving at
a given moment in time
–Speedometer in a car
**Average speed is computed
for the entire duration of a trip,
and instantaneous speed is
measured at a particular
instant.
Graphing Motion
• The slope of a line on a
distance-time graph is
speed.
Velocity
• Velocity- the speed and
direction in which an object
is moving
–Sometimes you need to know
the direction…If two trains are
traveling…
• Velocity is a vector.
Acceleration
• Acceleration-The rate of
change in velocity
–Changes in speed, direction or
both
– Can Increase or decrease, (be
positive or negative)
– acceleration = zero if it is moving at
the same speed in thesame direction
• Constant acceleration is a
steady change in velocity
over time.
–the velocity of the object
changes by the same
amount each second
–A jet taking off.
Calculating Acceleration
Vf = final velocity
Vi = initial (starting) velocity
Graphing Acceleration
• The slope of a speed-time
graph is acceleration
Can be linear or
non linear graph
#76 & 77 I will be able to
investigate the effect of speed
on the severity of a collision.
Vocabulary:
• Acceleration
• Force
• Balanced force
• Unbalanced force
• Net force
• Speed
• Momentum
• Conservation of momentum
Force
• force is a push or a pull that
acts on an object.
–can cause a resting object
to move
–can accelerate a moving
object (change in ____ &
____)
• Newtons(N)- measurement
of force
• One N is the force that
causes 1-kilogram (mass) to
accelerate at a rate of
1 meter per second each
second (1 m/s2).
• Unit for force:(1 N =
2
1 kg·m/s )
FORCE
• Balanced force- when forces
are balanced, net force = 0. No
change in motion (arm wrestle)
• Unbalanced force- causes
object to accelerate
FORCE
• NET FORCE - Combine
forces in the same direction,
(subtract in opposite direction)
• Ex. If two people are pushing a
cart at the same time, you
would combine.
• In a tug of war, the two forces
would be subtracted.
FRICTION
• Friction – force that opposes
the motion of objects that are
touching
–Static
–Sliding
–Rolling
–Fluid
GRAVITY
• Gravity – force that attracts or
pulls objects together
–Acts downwards toward
center of Earth
–Causes objects to accelerate
as they fall
Newton’s Laws
1st - An object at rest remains at
rest OR an object in motion
remains in motion,unless acted
on by an outside force
Newton’s Laws
• 1st law = Law of inertia.
• Inertia- tendency of object to
resist change in motion.
–Think seat belts, airbags, etc.
Newton’s Laws
• 2nd –acceleration of an object
depends on the force on the
object and the mass of the
object
• F= (m)(a) OR a= f / m
PRACTICE
• F = (m)(a)
• How much force is required to
move a car with a mass of
2
1200 kg at a rate of 3.0 m/s ?
• What is the force on a 80 kg
box accelerating down a ramp
at 2 m/s2?
Newton’s Laws
• Mass – measure of inertia,
amount of matter in an object
• Weight- force of gravity on an
object
• This formula is a substitute for
F= (m)(a)…
– g = 9.8 m/s2 (on earth)
• Units for weight = newtons (N)
Newton’s Laws
• 3rd – for every action or force,
there is an equal and opposite
reaction or force
–Bumper cars
–If the forces both act on the same
object the object will not move
(net force = 0)
MOMENTUM
•Momentum = units are kgm/s
•No velocity? no momentum!
•Describes how mass and velocity
are effected by each other.
Conservation of momentum-
• The loss of momentum in an
object is the gain of
momentum in another object