# Spark timers

#### captain_planet

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!

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#### Turtle

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.

#### captain_planet

i understand that, but acceleration is not constant and the v = d/t formula is for constant velocity...

#### Turtle

It is average acceleration sorry, for instantaneous acceleration use dv/dt and velocity use dr/dt.

#### HallsofIvy

Homework Helper
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.

#### captain_planet

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!

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