Questions simple pendulum 1 go to...

Go to https://phet.colorado.edu/sims/html/pendulum-lab/latest/pendulumlab_en.html and double click on "Intro." Make sure that the Stopwatch is checked. Adjust the length of the string to 0.70 m and the mass to 1.00 kg. The gravity should be that of Earth, and no friction should be applied. Move the mass to 5°. Start the stopwatch when the mass comes back to 5° and count ten oscillations, then stop the stopwatch. What is the period of the pendulum (take your number and divide by 10)? 2. Repeat this for a few angles. At what angle does the period start to change (when the small angle approximation no longer holds)? 3. Change the length of the pendulum to 0.4 m. What is the period at 5°? 4. Keep the length at 0.4 m, and change the mass to 1.3 kg. What is the period at 5°? Hooke's Law 5. What is the spring constant of a spring if the hanging mass is 0.100 kg and the displacement from equilibrium is 0.065 m?

Transcript

00:01 In this video, we're going to be looking at an online simulation of a simple pendulum.

00:07 Okay, so the website is, if you just google, instead of writing the whole thing out, google p -h -e -t -pendulum lab, okay, and that's what i googled, and i got right to it.

00:31 The website you should get to looks like this.

00:33 Okay, so you can see that we have our pendulum.

00:36 Up here is a protractor that will measure the angle for you.

00:41 And on the right hand side, we can vary the length of the pendulum, the mass of the pendulum, the gravitational force, and the frictional force.

00:51 Okay, what we're going to do is mess around with some of these settings and see what happens.

00:55 Okay, the first thing we want to do is set the length to l equals 0.

01:03 0 .7 meters.

01:06 Okay, we're going to set our mass m to 1 .0 kilograms.

01:15 Okay, and we're going to set our initial starting angle to 5 degrees, so theta equals 5 degrees, and that's with respect to the vertical, so 5 degrees is going to be somewhere like that.

01:30 Okay, and what we want to do is use the stopwatch over here to time 10 oscillations and from that i want to find the period of this pendulum.

01:41 Okay, so length is 7 meters or 0 .7 meters, sorry.

01:45 Mass is 1 kilogram and our initial angle from vertical is 5 degrees.

01:51 Okay, so when i do that, i get a period of t equals 1 .68 seconds.

02:01 Okay, and we can compare that to our theoretical equation for the period of a pendulum.

02:08 Okay, and that is t period equals 2 pi times the square root of the length of the pendulum divided by the gravitational acceleration.

02:22 Okay, so when i do that calculation out, i get a period of t equals 1 .68 seconds as well.

02:29 So our simulation matches our theory.

02:33 Okay, the next thing we want to do is repeat the same experiment, but we want to vary the starting angle, okay? but we want to keep the length and the mass of the pendulum the same.

02:46 And we want to look for an angle where the small angle approximation starts to fail.

02:53 Okay, so at which angle does the period start to become different than our one point? 68 seconds.

03:01 Okay, so i did this starting from 5 degrees and i went up in increments of 5.

03:06 So i went 5, 10, 15, 20, 25.

03:09 And i found the periods were all 1 .68 until just about, and i'll call this, theta critical, equals approximately 60 degrees.

03:21 Okay, that's when i saw the period become greater than 1 .68 seconds.

03:26 The next thing we want to do, i guess that was number two, so number three, is we want to change the length of the pendulum to l equals 0 .4 meters, right, and measure the period now.

03:44 I'm just looking at this equation for the period.

03:47 I would expect it to be less than 1 .68 seconds, okay, because our l has decreased.

03:53 So let's see what we get.

03:56 I get a period of t equals 1 .26 seconds...

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