# Calculating speed.

• Feb 12th 2010, 02:00 AM
Mystery
Calculating speed.
I currently have a machine that can calculate the time it takes for an object to travel one meter. (two lasers first one starts a timer second one stops it, The lasers are positioned exactly 1 meter apart.)

So if an object was going 10 M/s (Meters per second) it would take 0.1 of a second (10 nanoseconds) to travel one meter. If it was going 1 meter per second it would take 1 second, obviously.

What would the equation needed to turn the time taken into the speed (In Meters per second preferably)

http://i48.tinypic.com/ehcvm.png
For those interested the program used is called Algodoo
• Feb 12th 2010, 02:17 PM
skeeter
Quote:

Originally Posted by Mystery
I currently have a machine that can calculate the time it takes for an object to travel one meter. (two lasers first one starts a timer second one stops it, The lasers are positioned exactly 1 meter apart.)

So if an object was going 10 M/s (Meters per second) it would take 0.1 of a second (10 nanoseconds) to travel one meter. If it was going 1 meter per second it would take 1 second, obviously.

What would the equation needed to turn the time taken into the speed (In Meters per second preferably)

http://i48.tinypic.com/ehcvm.png
For those interested the program used is called Algodoo

$v = \frac{\Delta x}{\Delta t}$

also ...

0.1 sec does not equal 10 nanoseconds.

10 nanoseconds = $10^{-8}$ sec

0.1 sec = 100 milliseconds
• Feb 12th 2010, 02:57 PM
Mystery
So basically Velocity is the Distance Divided by the time taken.
:D thanks.
• Feb 12th 2010, 04:27 PM
Roam
However, it doesn't matter in this particular problem, because the laser travels one straight path. But generally in these problems you want the average speed. The formula $v = \frac{\Delta x}{\Delta t}$ gives you the "average velocity" of the object, $\Delta x$ is the object's displacement (change in position given by $\Delta x = x_f - x_i$). So the formula is not always the same thing as $\frac{d}{\Delta t}$ which gives you the "average speed"! Because in the latter formula, "d" means the total distance traveled which isn't always the same as displacement.
Here's an example: If a runner runs a distance d of 10 km and yet ends up at his starting point, his displacement is zero, so his average velocity is zero! But his speed is clearly NOT zero!