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!

Homework Help: Spark timers

  1. Sep 13, 2003 #1
    just a quick question on spark timers, mostly on ticker tape. I need a reminder on how to calculate the acceleration on the tape. i know i need to take a time measurement and the distance between the dots on the tape but from there do i need to calculate intervals or what? i'm using the acceleration to help find the coefficient of friction of a dynamics cart and brass mass on an inclined plane. thanks for the help!
  2. jcsd
  3. Sep 13, 2003 #2
    For acceleration it's velocity over time. So you need to find the velocity (distance over time).
    For example if I move 5 meters in 5 seconds my velocity is 1m/s, then for acceleration I put 1m/s over 5s, then my acceleration is 0.2m/s.
  4. Sep 13, 2003 #3
    i understand that, but acceleration is not constant and the v = d/t formula is for constant velocity...
  5. Sep 13, 2003 #4
    It is average acceleration sorry, for instantaneous acceleration use dv/dt and velocity use dr/dt.
  6. Sep 14, 2003 #5


    User Avatar
    Science Advisor

    Of course, since you only have discrete values for the marks (not a continuous function), you can't really use "dv/dt".

    What you need to do is find the average speed between each pair of marks: distance measured on the tape divided by the time interval.

    Now do the same for each pair of average speed values: subtract the two speeds and divide by the time interval.

    That gives the average acceleration over each interval and gives you an acceleration function between intervals.
  7. Sep 14, 2003 #6
    thanks for the help
    i figured out that the graph of the instananeous velocity of vs teh time at that speed will give me the slope equal to the acceleration. if i still sound confused please help but thanks for your replies!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook