 |
 |
Sensing and Datalogging for Science Education |
||
Sciencescope |
||||
|
Last updated 31st July 2008 Sensors Logbooks PriceLists Investigations 2008 Catalogue |
||||
| ||||||||||||
Relationship between distance, time and speedIn
order to understand motion, it is important to consider the basic definition in
terms of distance and time. When
we say a track event at the Olympics is 800 m long, we are defining its
distance. Yet the only thing people are interested in is the time taken to run
it. The
winner covered the same distance as other people in a shorter time. Equally, however,
we could consider them to have run a longer distance in the same time. Both
points of view are exactly the same. All
that we are talking about is their average speed, which is defined by: 
In
a race, they start from a position of rest, speed up, and run at almost the same speed
throughout. At the end, they sprint as fast as they can until the finish. A
simple calculation involving their total distance (800m) and their time (world
record = 86s) reveals nothing about the race itself. That’s why we talk about
average speed. In
everyday life we use speeds like miles per hour (mph), whereas in this race we
would use metres per second (m/s). It is the latter which we tend to use in
Physics. The
equation for speed can be remembered from the unit itself: m/s - m is metres
(distance); s is seconds (time). It can be rearranged to give:
We
write this in symbol form as d = s × t Instantaneous
speed is the speed of an object at a particular moment in time. It is measured
in metres per second (m/s). Sometimes
when we are describing motion we use the terms "steady
speed" or "constant
speed". An object is travelling at a steady or constant
speed when its instantaneous speed has the same value throughout its journey.
For example, if a car is travelling at a constant speed the reading on the car's
speedometer does not change. The speedometer reads the speed of the car at each
moment in time throughout the car's journey. Describing
a journey made by an object is very boring if you just use words. As with much
of science, graphs are more revealing. You are going to plot distance against
time.
These show how the Distance sensor was set up to study the speed.
View and/or download the worksheet If you cannot access 4shared.com please contact us, by email, and we will get this page to you via another route. View and/or download the Datadisc file examples of this investigation. Three steady speeds (with fitted functions and speed graph) Two steady speeds (with fitted functions and speed graph) Two steady speeds in the same recoding (you must have Datadisc installed to view the file, downloadable from Download Centre) |
|
|
