1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Measuring linear velocity of a toy car

  1. May 14, 2012 #1
    I want to measure the linear velocity of a toy car.. i had a thought over it..
    i m thinking of using a optical mouse to do so , i need to process the usb output , how shud i do it ?.. and can there be any other cheap way of doing it..?
  2. jcsd
  3. May 15, 2012 #2
    You could do it accurately and cheaply using 2 LEDs, 2 Phototransistors, a dual Op-amp configured as 2 comparators and a 3.5mm mini jack and a bit of audio cable to go into your computer's Audio In.

    Point an LED at a Phototransistor at the part of the car's run where you want the test to start and put the other one a little way ahead of it. Set the car running and use a sound recorder to sample the clicks made by the comparators as they trigger at the breaking and remaking of each of the LED beams. Look for the start of each event and record the time. Then look for the end of each event and record the times as accurately as you can.

    Add the times together (front of car goes past each LED, back of car goes past each LED) and divide by two to get the average.

    Measure the distance between the LEDs as accurately as you can.

    The linear velocity of the car is the distance travelled divided by the time taken.

    Total cost - less than 5 dollars.

    Have fun.
  4. May 17, 2012 #3
    i basically want to measure its speed with a independent system mounted on the car.. i want to get the velocity at every instant which is required for further processing of my algorithm...
    so using the led system every time wont do..
  5. May 20, 2012 #4


    User Avatar
    Gold Member

    What ever happened to the way that we used to do it, with a stopwatch and a ruler?
  6. May 23, 2012 #5
    i was thinking of using a GPS module....but i need some other methods as GPS is costly
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook