Download 8th Grade Chapter 2 Notes on Motion

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8th Grade Chapter 2 Notes on Motion
Motion: when an object changes its position relative to a
reference point.
Position: place where something is located
Reference Point: a point of interest.
An object’s position and reference point describe distance
traveled.
a. Distance: how far an object has moved, expressed in
meters or kilometers.
b. Displacement: the distance & direction of an
object’s change in position from the starting point.
*****distance = displacement IF an object is moving
in a straight line*****
Finish Line
________________ 80m
________________ 70m
________________ 60m
________________ 50m
________________ 40m
________________ 30m
__________________ 20m
__________________ 10m
Start Line
Displacement = 40 m N of starting
Distance traveled = 120 meters
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Speed: the distance an object travels per unit of time.
Speed = distance, meters
Time, seconds
S= d
t
rate: any change over time.
A car is traveling at a constant speed & covers a distance of
750 meters in 25 seconds. What is the car’s speed?
Given: D=750 m
T = 25 s
S=?
S=d m
t sec.
S=d/t; S= 750m/25sec; S=30m/sec
Types of speed
a. Constant Speed: speed that remains the same-not
speeding up or slowing down; cruise control.
b. Changing speed: speed that varies and doesn’t stay
the same.
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c. Average Speed: speed of motion when speed is
changing.
Average speed = total distance
total timed.
d. Instantaneous Speed: speed at any given point in
time; speed read from a speedometer.
Graphing Motion
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Velocity speed AND direction of motion
A
B
A=B speed
A opposite B direction so velocity is different
Acceleration: the rate of change of velocity; Δ V
a. Positive Acceleration speed is increasing
b. Negative Acceleration (Deceleration) speed is
decreasing
Calculating Acceleration
Change in velocity = final velocity – initial velocity
ΔV=Vf-Vi
To calculate acceleration (meters) = Vf-Vi
sec²
t
A=Vf-Vi
t
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* If positive acceleration, A will be a positive number
If negative acceleration, A will be a negative number*
How are forces and motion related?
Force: a push or a pull on an object.
Do Objects always move in the same direction of a force?
Two types of forces:
1. Balanced forces: forces that are = in size and
opposite in direction
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2. Unbalance forces: forces that are ≠ in size and
either opposite or same in direction.
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Net Force: when 2 or more forces act on object at the same
time, the forces combine to form the net force.
Inertia: the tendency of an object to resist any change on
its motion.
Bowling ball versus ping pong ball…same inertia???
Bowling ball has a > inertia because the > an object’s mass,
the > its inertia.
Newton’s First Law of Motion: an object at rest will stay
at rest, an object in motion will stay in motion unless it is
acted on by an unbalanced force.