Trying to create a simple pendulum angle output on excel

[shocklightnin]

Homework Statement

Trying to create an excel spreadsheet that outputs the angles of a simple pendulum as it slowly comes to a stop.

Homework Equations

so I've used the formula:
θ(t) = θ0cos(squareroot(g/R*t)

where:
θ0= inital angle
g=gravity constant
R= length of string
t=time
i got it off of this website:
http://www.myphysicslab.com/pendulum1.html -where its the answer to the third question.

The Attempt at a Solution

Ive input all of this into a spreadsheet in excel, i was wondering if this is the right equation just to see the output of the angle's descent as the pendulum comes to a stop.

so say you're inital angle is at 90 degrees (you're holding the mass/ball at 90 degrees and then you let it go)
the degree at which it keeps going back and forth from will eventually decrease to zero right? i was just wondering if this was the correct equation for this. if not, could you please help me out?

and if it is:
i have modified the spreadsheet so that the first output of angle in excel will become the next lines' inital angle and repeated it for the following lines. is this a correct way to do this? the output degree does indeed decrease but very slowly. i was just wondering if this is correct.

thank you for your time.

 

[Redbelly98]

I'm a little confused as to what you are doing.

... I've used the formula:
θ(t) = θ0 cos[squareroot(g/R)*t]

(Note, I have corrected the parentheses in the formula)

If you use that equation, the pendulum will keep oscillating and not come to a stop. It's just the cosine function, which is periodic, and its amplitude remains constant for all time. There is no need to take a starting θ value and use it to calculate θ in the following time increment.

To graph θ(t) in Excel, just make a column of time values and a column of θ values using the equation and some suitable values for θo, R, and g. Take note, Excel uses radians when doing trig calculations.

 

[shocklightnin]

Alright, thank you so much for your help.

I just have another question, I've input everything as you said--is it normal for the final out put to have negative values?

thanks again.

 

[Redbelly98]

You're welcome.

It's the cosine function that is being graphed, are you familiar with it? It is perfectly normal for the cosine to have negative values part of the time.