Trying to build a timer switch

[Steven L Coulombe]

I'm looking to build a timer for my science class that needs to be quite accurate. I'd like it to start as an object is released, and stopped again once it stops. I want to be able to calculate average speed. I have no idea what components I would need to accomplish this. Buying one would be easier, but I don't even know what to search for.

 

[Sadlercomfort]

Average Speed = Total Distance / Time

If you are trying to measure falling objects you will find they all fall at the same rate.

Are you trying to measure the speed of an object which travels along a surface?

 

[KMoffett]

"If you are trying to measure falling objects you will find they all fall at the same rate."

Only in a vacuum!

Ken

 

[Sadlercomfort]

Only in a vacuum!

Of course Still the velocity difference would be negligible, unless dropping two objects from a great hieght or having a large difference in surface area in the objects.

 

[KMoffett]

Steven,

If you want to buy one, Google: photogate
There are commercial ones like: http://www.novatech-usa.com/Products/Mechanics-Educational/DTPHG1?gclid=CIC4q_HW8MoCFdcYgQod4nAOoQ
I've used cheap stopwatches to time periods. Used LEDs or laser pointers and a photo transistors to detect the start and stop events. Photo transistor drives a MOSFET. The is MOSFET placed across the stopwatch's start-start switch contacts. How accurate do you need the time to be? I think stopwatches are good to 100th of a second. But this requires some electronics skill.

Ken