Transcript Ch. 2 Motion

Ch. 2 Motion
2.1 Describing Motion
2.2 Acceleration
2.3 Motion and Forces
2.1 Motion
► Distance
(meters) and Time (seconds)
► Object changes position relative to a
reference point.
 Displacement: distance and direction of an
object’s change in position from the starting
point.
 Cops need reference point to clock speeders
Speed
► Speed
in a reference frame (stationary
background)- distance traveled over time
S=d/t
► Constant
(m/s
mi/hr)
Speed-object covers equal
distance in equal amounts of time.
► Distance Time Graph:
► Constant
Speed cannot really occur:
 Forces (friction, air resistance, etc)
VELOCITY
► Speed
with direction
 Ex. 4.5 m/s to the north
 2.0 km/h to highway 400 Southbound
Calculations
1.
2.
3.
Mr. Keller runs with a bunny towards his
kitchen which is 200 m. away in 40
seconds. What is his speed? What is his
velocity?
Mr. Keller rides his scooter at a constant
speed of 20 mi/hr. How long does he take
to travel 5 miles?
How far does Batman fall in 10 minutes at
speed of 5 m/s?
2.2 Acceleration
► Change
in velocity: Object changes its speed,
direction, or both.
A= (vf – vi)/t
(m/s2)
Speeding up: Positive Acceleration
 A zebra is standing still eating grass and takes off running
at 3 m/s north away from the scary lion over 120 seconds.
What is the acceleration of the zebra?
► Slow
down: Negative Acceleration
 A dying zebra is walking south at a rate of 2 m/s when it
dies 20 seconds later. What is the acceleration of the
zebra?
► Change
in direction: Change in Acceleration
Calculations
1. A ball is dropped from a cliff and has an
acceleration of 10 m/s2. How long will it
take the ball to reach a speed of 30 m/s?
2. A beaver leaves its hole with an
acceleration of 4 m/s2. What is the beavers
speed 5 seconds later?
2.3 Motion and Forces
► Force:
push or pull.
Force=change in motion=Speed or Direction
► Balanced Forces: No motion= Net force= 0
► Unbalanced
Forces: Net force=motion
Inertia and Mass
► Inertia-
NEWTONS 1st Law:
Object moving at a constant velocity
keeps moving at that velocity unless an
unbalanced net force acts on it. An
object at rest stays at rest unless an
unbalanced net force acts on it.
► The
greater the mass, greater inertia.
Calculations
1.
Two students push on a box in the same
direction, and one pushes in the opposite
direction. What is the net force on the box
if each pushes with a force of 50 N?
2.
The downward force of gravity and the
upward force of air resistance on a dead
beetle are both 5 N. What is the dead
beetle’s acceleration?
Ch. 2 Homework Problems
►Page
834
►#’ers
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