Unit 2: Motion-- Speed and Velocity and Acceleration
What’s the difference between distance and displacement?
Distance: the total magnitude traveled (length without direction)
Displacement: the shortest distance from the starting point to the ending point
Position: where an object is, including direction, compared to where it was
Ladybug Example
What is speed?Speed–The rate of change in distance with respect
to time.Non moving objects: speed = 0 m/sUnits: m/s, cm/s, mphSince speed is built from distance, a scalar
quantity, then speed is also a scalar quantity. Scalar Quantities carry no direction information
with them.
What is Velocity?The rate of change in displacement with respect
to time. Since displacement is a vector quantity, then
velocity is also a vector quantity. v=d/t
v= velocity (m/s)d= distance (m)t= time (s) D
V T
Speed & Velocity ExamplesSpeed is distance divided by time
2 cm/s
Velocity includes the direction2 cm/s west
West
What is the difference between average velocity and instantaneous velocity?
Average Velocity: The longer the time period measured, the more it leads to calculating an average velocity.
Instantaneous Velocity: The shorter the time period measured the closer it brings you to calculating an "instantaneous velocity". Only if the time period becomes zero would we truly have an instantaneous velocity.
Acceleration“Acceleration” occurs
when your speed changes up or down (or when you change direction).
It is the rate speed changesLevel ground- no
acceleration due to gravity
Steep down hill- acceleration due to gravity
Steeper hill= more acceleration
Deceleration is slowing down
Zero acceleration is at a constant speed AND not changing direction
Acceleration
Can use a graph to show acceleration+ slope = +acceleration (speed up)- slope = - acceleration (slow down)0 slope = no acceleration
Acceleration= change in speed (cm/sec)time (sec)
a = vf-vi
tUnits: cm/sec*sec or cm/sec2
Free Fall- Drop straight downAcceleration due to
gravity 9.8 m/sec2
Terminal Velocity- Highest velocity reached by a
falling objectWhen an object stops
accelerating, but continues to fall
When air resistance balances the pull of gravity
Projectiles
An object that is sent through the air is a projectile
The path of a projectile is called a trajectory
In the absence of air resistance, all objects fall with the same uniform acceleration = 10 m/s2
Two objects of different sizes and weights, dropped from the same height, will hit the ground at the same time.
Resolving VectorsTo add vectors (going in same direction): line up tail to tip
and add the numbers & keep the direction the same. Ex: 4 m N + 3 m N = 7 m N
To subtract vectors (going in opposite directions): Subtract smaller # from larger # and keep direction of the larger #. Ex: 15 m S - 3 m N = 12 m S
If the vectors are at right angles to each other, line up tail to tip and find the hypotenuse (Remember a2 + b2 = c2 and then solve for c) and combine the directionsEx: 3 m N + 4 m E = 32 + 42 = c2 25 = c2 5 m
NE = c