Transcript MOTION - pdsd.org

Motion
p.272 -273 in red text
#13.1 worksheet accelerated
Speed activity
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
MOTION
• Distance the length of a path
between two points.
–Si units:(METRIC) km, m, mm, cm,
etc.
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
• 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.
Answer
•
•
•
•
S= d/t
60 km + 35km = 95km
.8hr + .5hr = 1.3hr
S= 95/1.3=
73km/hr
Speed Activity
• In class or track:
• Run a predetermined distance, measure time
with a top watch.
• Two trials each. Any motion you choose.
• Calculate speed for you and your partner.
• Calculate speed for your group.
• Calculate speed for the class.
Velocity and Acceleration
•
•
•
•
P. 274-275 in red text
#13.2 accelerated
#11.2 honors
Velocity and acceleration enrichment
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.
– A rollercoaster dropping down the first hill.
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
Newton’s law’s
• P. 280 1st law
• P. 282 2nd law
• P. 284 3rd law
• Crash test dummies
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
• Acceleration =changes in
____ and/or ____
• Newtons(N)- unit for force
• One N is the force that
causes a 1 kg object to
accelerate at a rate of
1 meter per second every
second (1 m/s2).
–1 N = 1 kgm/s2
FORCE
• NET FORCE – Combination of
forces in the same direction or
opposite directions
• Ex. If two people are pushing a
cart at the same time…
FORCE
• Balanced force- when forces are
balanced, net force = 0. No
change in motion (arm wrestle)
• Unbalanced force- causes a
change in motion
FRICTION
• Friction – force that opposes
the motion of objects by
contact
–Static
–Sliding
–Rolling
–Fluid
–
http://www.planet-science.com/text_only/under_11s/friction.html
• Paradoxically, friction is one of those things that's so
prevalent, so ubiquitous, that it's hard to think of any. But
here are a few that come immediately to mind:
• 1. Air resistance: friction between a moving body and
molecules of air.
2. Rubbing: Rubbing your hands together to create warmth.
3. Tire traction: the friction between the tires and the surface
of the road that allows your car to accelerate, slow down, and
negotiate turns and corners.
4. Static friction: the friction between two surfaces that
prevents items on less-than-perfectly-level tables and shelves
from sliding off. Also, the friction between the soles of your
shoes and the ground that permits you to walk without
busting your butt. (Similar to 3 and 4.)
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 is called the Law of Inertia.
• Inertia- tendency of object to
resist change in motion.
–seat belts, airbags, etc – these
objects protect you from inertia.
Newton’s Laws
• 2nd – the acceleration of an
object depends on the force
acting 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
1200 kg at a rate of 3.0 m/s2?
• What is the force on a 80 kg
box accelerating down a ramp
2?
at 2 m/s
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)b
Newton’s Laws
rd
• 3 – 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 - describes how mass
and velocity are affected by each
other.
• units are kgm/s
•No velocity? no momentum!
•Conservation of momentum-
The loss of momentum in one
object is the gain of momentum
in another