Unit 2: Motion-- Speed and Velocity and Acceleration

What’s the difference between distance and displacement?

Distance: the total magnitude traveled Displacement: the shortest distance

from the starting point to the ending pointDraw & label this picture on the top half

of your left page

What is speed? Speed–The rate of change in distance with respect

to time. Even objects that are not moving have a speed = 0

m/s Units: m/s, cm/s, mph Since 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.  Vector Quantities have both magnitude and

direction. v=d/t

v= velocity (m/s)d= distance (m)t= time (s)

Draw the triangle on your left page!

D

V T

Speed & Velocity Examples

Speed is distance divided by time 2 cm/s

Velocity includes the direction 2 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. 

Using Graphs to Calculate Speed

We use graphical models to predict speed Graphical- mathematical model

Independent on x axis; what you change/test (MIX) Dependent on y axis; what you measure (DRY)

Position- where an object is, including direction, compared to where it was

Distance- length w/o regard to direction Can get speed from slope of position versus time

graph Slope = Rise/run

Acceleration“Acceleration” occurs

when your speed changes up or down (or when you change direction).

It is the rate speed changes Level 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

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

t

Units: 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 fallWhen air resistance balances the pull of gravity