# Question about Terminal Velocity Lab- without motion sensor

1. Feb 25, 2013

### Jaimie

Hello,
We are doing a lab studying terminal velocity. Unfortunately we do not have a motion sensor, so we are dropping coffee filters at a certain height (both scrunched and flat- while increasing their numbers), and noting their final speeds.
The thing I don't quite understand is whether and how the final speed is the terminal speed Can anyone advise? I believe it is so because this is what we've been measuring throughout our experiements. But other than that- I thought terminal velocity was that when both frictional force and gravity are equal.
Thank you!

2. Feb 26, 2013

### cepheid

Staff Emeritus
You do realize that "final" and "terminal" mean the same thing? :tongue: It's called the terminal velocity because it's the last one that is reached.

Initially, when the thing is first dropped, it accelerates, because of gravity. However, the faster it goes, the larger the drag force is. The drag force is upwards, countering gravity. Eventually, the drag force will get so large, that it will be equal in magnitude to the force of gravity. At this point, there will be NO NET FORCE on the object (because the drag force and gravity will cancel each other out). If there is no NET force, then there is 0 acceleration (cf. Newton's 2nd Law). So, the object stops speeding up and just continues to fall at a constant velocity for the rest of the fall. That's why this is the "terminal" velocity. It can't be exceeded.