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Chapter 2
Energy & Motion
Egg Drop competition
Section 1
I. Motion: Everything in the
universe has motion!
• How would you
describe motion?
Motion & distance are
important.
• In order to win a race,
you must cover a
distance in the shortest
amount of time.
4 types of motion
1. Motion & Position
You don’t need to see
something move to
know that it is moving
• A reference point is
needed to
determine the
position of an
object.
4 types of motion
2. Relative Motion
Not all motion is
observed.
You are not moving
relative to your desk or
your school building,
but you are moving
relative to the other
planets in the solar
system and the Sun.
4 types of motion
3. Distance
The motion of an object
as it is described to how
far it has moved.
The SI unit of distance is
Meter. Longer distances
is kilometer
4 types of motion
4. Displacement
suppose a runner jogs
to the 50 m mark &
turns around to run
back to the 20 m mark.
He has ran a total of 70 m.
Displacemetn includes
distance & direction
from the starting point
II. Speed: describes how fast an
object is moving
• Types of speed
1. Rate: any change over
time
If you think of distance as
the change in position,
then speed is the rate at
which distance is
traveled or the rate of
change in position.
Calculating Speed
• Speed is related to the
distance traveled at the
time needed to travel
the distance
• Suppose you ran 5 km
in 10 min. Calculate the
speed.
Motion of constant speeds
• If a car neither speeds
up or slows down it is
moving at a constant
speed.
• Just look at the
speedometer
Average speed
• Speed of motion when
speed is changed.
• The total distanced
traveled divided by the
total time of travel
Instantaneous speed
• Is the speed given at the
point in time.
• The speed you are
going at a certain time.
• Example: the car’s
speedometer
Changing Instantaneous speed
• When something speeding up or slowing
down is changed
• The speed is different at every point in time
Practice ( page 42)
• Sound travels at a speed of 330 m/s. If a
lightning bolt strikes the ground 1 km away
from you, how long will it take for the sound
to reach the ground?
Distance, d = 1 km or 1000 m
Speed, s = 330 m/s
S = d/t
t = d/s
t = 1000 m / 330 m/s
t = 3.03 s
Graphing Motion
• The motion of an
object over a
period of time can
be shown on a
distance-time
graph.
Click image to play movie
• Time is plotted along the horizontal axis of
the graph and the distance traveled is
plotted along the vertical axis of the graph.
Distance-Time Graph
• Slope:
the steepness of a line
of a graph is called the
slope.
On the distance-time
graph, the slope of the
line representing the
motion of an object is
speed
• Changing Speed:
The lines in which is a
break shows that time
was used without
speed.
Velocity
• Is a speed in a given
direction. This includes the
speed of an object and the
direction of its motion
• Velocity = distance/time
V = d/t
NOAA tracks hurricanes &
forecast its internal speed and
direction.
The speed of the hurricane is 20 km/h, and
The velocity is 20 km/h North, by North East
Acceleration, Speed & Velocity
Egg Drop competition
Section 2 & 3
Acceleration:
• is the rate of change • 2 types of acceleration
A . Positive Acceleration
of velocity.
(faster)
• When the velocity of
an object changes,
B. Negative Acceleration
the object is
(decreasing speed)
accelerating.
Acceleration has a
• Has a direction &
velocity
• Acceleration = change
in velocity / time
• Always subtract the
initial velocity
(beginning) from the
final velocity (ending).
Calculating Acceleration
• Then the change in velocity is:
• Suppose a jet airliner starts at rest at the end
of a runway and reaches a speed of 80 m/s in
20 s. Because it started from rest, its initial
speed was zero.
•
Calculating Positive Acceleration
• The airliner is
speeding up, so the
final speed is
greater than the
initial speed and
the acceleration is
positive.
Calculating Negative
Acceleration
• A skateboarder is
moving in a straight
line at a constant speed
of 3 m/s and comes to a
stop in 20 seconds.
• The skateboarder is
slowing down, so the
final speed is less than
the initial speed and the
acceleration is negative.
• The acceleration always
will be positive if an
object is speeding up and
negative if the object is
slowing down.
Amusement Park Acceleration
• Engineers use the laws of physics to design
amusement park rides that are thrilling, but
harmless.
• The highest
speeds and
accelerations
usually are
produced on
steel roller
coasters.
Practice
What is the acceleration of a hockey player who
is skating at 10 m/s and comes to a complete
stop in 2 s?
A=
(0 m/s – 10 m/s) = – 5 m/s
2s
Section 3
Motion and Force
Newton’s 1st Law of Motion
What is force?
• Force is a push or pull that one body exerts
on another
• Example: passing a basketball to a team
member requires force
• The applied force results in the movement of
the object.
3 types of motion
• Changing motion:
Changing the motion of
an object when you
exert a force on it.
Ex: when a racket strikes
a tennis ball with a
force that will cause the
ball to stop & move in
the opposite direction
3 types of motion
• Balanced Force
Forces do not always
change velocity.
If two students push on a
box at the opposite
sides the force is equal
• When two or more forces act on an object at
the same time, the forces combine to form the
NET FORCE
3 types of motion
• Unbalanced Force
When two students are
pushing with unequal
forces in the opposite
direction a net force
occurs in the direction
of the larger force
OR
• Unbalanced Force:
When two students are
pushing in the same
direction the forces are
combined or added
together because they
are exerted in the same
direction
INTERIA
• Inertia (Newton’s 1st Law of Motion) is the
tendency of an object to resist any change in
its motion. If an object is moving, it will
continue moving at the same force unless an
unbalanced force acts on it.
Newton’s 1st Law of Motion
• An object in motion stays in motion; An
object at rest, stays at rest unless acted on by
an outside force
• The British scientist Sir Isaac Newton (1642–
1727) was able to state rules that describe the
effects of forces on the motion of objects.
• The law of inertia can explain what happens
in a car crash.
• When a car traveling about 50 km/h collides
head-on with something solid, the car
crumples, slows down, and stops within
approximately 0.1 s.