Centripetal force apparatus lab

[MickeyGoh]

Actually, I am going to do a centripetal force apparatus lab tmr morning.
Here I get some pre-lab questions.

In this lab, we are going to use economy force sensor (as I know there are 2 types, but it doesn't matter).
There is one question related to this sensor...
It says "The 'Tare' button on the economy force sensor is to set the force to be zero. How to verify the result? Hint: Observe the curve."

First question, what result? That the force is really zero? Is the voltage of the electric motor 0V indicating that the force is 0N?

Second question, what curve? I don't get the relation of it with voltage. Or is it not related to the voltage?Besides, in the experiment of Centripetal force vs Mass, there is a question asking whether the velocity is a constant or not. It seems an easy question and I should know...
But somehow I forget it. Is the velocity increasing with the radius and thus keeping v²/r a constant? Or both v and r are constants so that v²/r is already a constant?

Thank you.

 

[jtbell]

It says "The 'Tare' button on the economy force sensor is to set the force to be zero.

On the force sensors that I've used, the button simply sets the display to read zero, for whatever value the actual force is at that moment. You normally use it by first ensuring that there is no force being applied to the sensor (e.g. by letting a string tied to it go slack), then pressing the button.

As time passes, this "zero setting" tends to drift so that when no force is applied, the sensor reads a small nonzero value. Therefore I always make sure to reset the zero frequently during the course of the experiment.

 

[MickeyGoh]

But do you know what the question wants me to answer?

 

[MickeyGoh]

for the velocity one, i think i get it.
Since v = 2πr / t
so if r is unchanged, v will not be changed. i.e. kept constant

 

[MickeyGoh]

or simply to say
as centripetal force vs mass, v²/r is constant
as r is unchanged, v should be unchanged to keep v²/r constantbut i still don't get the 'tare' button question