Definitions:
Speed
or Velocity?
Speed
is the rate of motion, or the rate of change of position.
It is expressed as distance moved (d) per unit of time(t).
Speed is a scalar quantity with dimensions distance/time.
Speed is measured in the same physical units of measurement
as velocity, but does not contain an element of direction.
Speed is
thus the magnitude component of velocity. Velocity contains
both the magnitude and direction components.
Common
speeds of
moving objects
For human
beings, an average walking speed is about 3 mph (~5 km/h,
1.39m/s),
The speed of long distance jogging for average persons is
about 6 mph (~10 km/h, 2.7 m/s).
Top athletic sprinters can run at 23.03 mph (~36.85 km/h,
10.24 m/s) within a short distance such as a 200 meters dash.
Cycling can average 12 mph (~20 km/h, 5.56 m/s)
Car can average 65 mph (~104 km/h, 28.9 m/s ) on highway
A 747
Airplane has an average speed 565 mi/hr
Acceleration
Acceleration,
(symbol: a) is defined as the rate of change of velocity.
It is thus a vector quantity with dimension length/time˛.
In SI units, acceleration is measured in meters/second˛.
To accelerate
an object is to change its velocity, which is accomplished
by altering either its speed or direction (like in case of
uniform circular motion) in relation to time. Acceleration
can have positive and negative values. Any time that the sign
(+ or ) of the acceleration is the same as the sign of the
velocity, the object will speed up. If the signs are opposite,
the object will slow down. Acceleration is a vector quantity.
When either velocity or direction changes, there is acceleration
(or deceleration).
To accelerate
an object requires the application of a force.
Graphing
Velocity and Acceleration
A car accelerates
from rest. The following two graphs are created using a java
applet (see below).



The
graph of velocity (m/sec.) vs. time (sec.) is
a straight line for accelerating objects.
acceleration
= velocity / time
What
is the slope of this graph? 
Please
enter your answer in the space provided:


The
graph of distance (x) vs. time (t) is a curve
where the equation of motion is:
x
= 1/2 at˛. What value of (a) would you
expect for this graph?
Hint:
For each value of t (in s), there is only one
value for x (in m). Pick any ordered pair for
t and x and substitute them into the above equation.
Then solve for a. 

Create
your own graphs for accelerating objects using the following
java
applet: 

This Java applet shows a car moving with
constant acceleration. The green control panel contains
text fields where you can vary the values of initial position,
initial velocity and acceleration (don't forget to press
the "Enter" key!). By using the buttons at the top right
you can bring back the car to its initial position or
stop and resume the simulation. The diagrams illustrate
the motion of the vehicle: Position x versus time t Velocity
v versus time t Acceleration a versus time t 

ACCELERATION
LAB EXERCISE:
This
is an excellent laboratory exercise for Middle and
High School students:
Problem:
What is the relationship between the distance an accelerating
object travels and the time it takes to travel that
distance?

