Transcript Ch3 Fill-in Notes

Ch. 3 Fill In Notes
Please Fill in the Blanks
Starting on page 33 of your
packet.
Section 1 – Describing Motion
A.Motion occurs when an
object changes its position.
1. Motion is measured relative
to a reference frame; a
group of objects that are not
moving relative to each
other.
Section 1 – Describing Motion
1. An object’s position is it’s
distance and direction
relative to one reference
point in the reference frame.
2. Distance is the length of the
path an object travels.
Section 1 – Describing Motion
3. Displacement is the
distance and direction of an
object’s final position from
its initial position.
a. A vector is a physical
quantity that includes both
size and direction.
Section 1 – Describing Motion
B. Speed, the distance an
object travels per unit of
time is measured as meters
per second (m/s) in SI units.
Section 1 – Describing Motion
1. Calculation:
speed = distance/time
2. Speed changes as an object
moves from one place to
another.
Section 1 – Describing Motion
3. Instantaneous speed is
speed at a single instant in
time.
a. Car speedometers measure
instantaneous speed.
Section 1 – Describing Motion
4. Average speed is how
quickly an object moved
over the entire distance
traveled.
a. To calculate it, divide total
distance traveled by the
total travel time.
Section 1 – Describing Motion
C.Velocity is the speed of an
object and its direction of
motion.
1. Like displacement, it is a
vector that has size, which
is the object’s speed, and
has a direction.
Section 1 – Describing Motion
2. Velocity can change if the
speed and/or direction of
the object changes, and can
change if the speed of the
object remains constant.
Section 1 – Describing Motion
D.A distance-time graph
shows the motion of an
object over a period of time.
1. We plot time on a
horizontal axis and distance
on a vertical axis.
Section 1 – Describing Motion
2. On the graph, speed is
represented by the slope, or
steepness, of the line.
Discussion Question:
How can we have a constant
speed with a changing
velocity?
Section 1 – Describing Motion
How can we have a constant
speed with a changing
velocity?
A: We change the direction of
the object’s motion.
Section 2 Acceleration
A. Acceleration is the change
in velocity divided by the
time it took for the change
to occur.
1. It has a size and direction,
so it is a vector (like
displacement and velocity).
Section 2 Acceleration
a. Its size is the change in
velocity.
b. Its direction is the direction
of the object’s motion.
2. Acceleration occurs when
an object’s speed and/or
direction of motion changes.
Section 2 Acceleration
a. When acceleration and
velocity move in the same
direction, speed is
increasing.
b. When acceleration and
velocity move in opposite
directions, speed is
decreasing.
Section 2 Acceleration
3. For example, the direction
of Earth’s velocity around
the Sun is continually
changing, so Earth is
accelerating.
Section 2 Acceleration
B. If the direction of motion of
an object doesn’t change,
you can calculate its
acceleration as follows…
1. Average acceleration =
(final velocity –initial
velocity)/(final time –initial
time)
Section 2 Acceleration
2. a = (vf – vi)/(tf – ti)
3. In SI units, acceleration
uses meters per second
2
squared (m/s ).
4. Acceleration is plotted on
speed-time graphs.
Section 2 Acceleration
a. We plot an object’s speed
on the vertical axis.
b. We plot an object’s time on
the horizontal axis.
5. If speed is increasing, final
speed is faster than initial
speed and acceleration is
positive.
Section 2 Acceleration
a. Slope is positive on speedtime graph.
6. If speed is decreasing, final
speed is slower than initial
speed and acceleration is
negative.
a. Slope is negative on speedtime graph.
Section 2 Acceleration
C. Multiple steep drops and
inversion loops in roller
coasters produce large
accelerations.
Section 2 Acceleration
Discussion Question: Is the
moon accelerating around
the Earth?
Section 2 Acceleration
Discussion Question: Is the
moon accelerating around
the Earth?
Answer: Yes, since it is
constantly changing
direction.
Section 3 Motion and Forces
A.Force is the push or pull
that one object exerts on
another object, measured in
newtons (N). {kg●m/s2}
1. Force causes a change in
motion or velocities.
Section 3 Motion and Forces
2. Net force is created when
two or more forces act on an
object at the same time.
3. Balanced forces are equal
in size and opposite in
direction: their net force is
zero.
Section 3 Motion and Forces
4. Unbalanced forces are
combined forces that cause
the velocity of an object to
change.
B. Friction opposes the
sliding motion of two
surfaces in contact.
Section 3 Motion and Forces
1. It is an unbalanced force
that decreases the speed of
an object.
2. Microwelds form on bumps
and dips in contacting
surfaces, causing them to
stick together.
Section 3 Motion and Forces
3. Static friction prevents two
surfaces in contact from
sliding past each other
because force cannot break
the microwelds between the
two surfaces.
Section 3 Motion and Forces
4. Sliding friction is a force
that acts in the opposite
direction to the motion of a
surface sliding on another
surface and is a smaller
force than due to static
friction.
Section 3 Motion and Forces
5. Rolling friction created
when an object rolls over a
surface, is usually a much
smaller force than sliding
friction.
Section 3 Motion and Forces
C.Air resistance is the
frictional force that opposes
motion of objects that move
through the air.
1. It causes objects to fall
with different accelerations
and speeds.
Section 3 Motion and Forces
2. It acts in the direction
opposite to the velocity of
an object moving in air.
3. Air resistance on an object
depends on its speed, size,
and shape.
Section 3 Motion and Forces
D. Terminal velocity is the
highest velocity a falling
object will reach. When the
net force on a falling object
from the upward force of air
resistance and the
downward force of gravity is
zero.
Section 3 Motion and Forces
Discussion Question: Which
has a larger frictional force,
a skater gliding on ice at the
beginning of a skating
session of the same skater
at the end of the session?
Why?
Section 3 Motion and Forces
Discussion Answer: At the
end, because the surface of
the ice has more bumps and
dips, creating stronger
microwelds.