Using the Quicktime player watch carefully the video clip A????1Conservation of Energy in a PendulumA????1 in the following web site link:
http://serc.carleton.edu/student_videos/index.html#energy
Here is a youtube version: https://youtu.be/EPEtEOVLarg
Watch 3 or 4 times the video.
Let us use energy-work concepts to analyze this situation.
Let us start defining the system: What do you want to select as the physical system of interest:
1) the pendulum only
2) The pendulum and the Earth together
I choosed the pendulum only
What is the external force acting on the system?
Consider the process when the pendulum goes from its initial position to its maximum height on the other side.
Draw a qualitative LOL energy bar chart for this process.
Write down the energy-work equation for this process.
The mass of the pendulum bob is 450 g.
What is the maximum gravitational potential energy of the bot-earth system when the bob is at the high point on the right side?
What is the kinetic energy of the pendulum-earth system when the mass goes through the lowest point during the second pass, when is possible to do measurements?
What is the mechanical energy at this position?
What is the kinetic energy of the pendulum-earth system when the mass goes through the lowest point during the third pass, the second time when is possible to do measurements?
What is the gravitational potential energy at this position?
What is the mechanical energy at this position?
What are the gravitational energy and the kinetic energy when the bob reaches its highest positon on the right side?
What is the total mechanical energy at the highest position on the right side?
What is the percent loss of mechanical energy during this full swing, that is, when the pendulum bob goes from its highest position on right side and returns to it?
What is the increase in thermal energy of the system?
From these results, do you have to make any change to your energy-bar LOL diagram?
Do you have to make changes to the energy equation for the pendulum bob-earth system?
About how many times will the pendulum go back and forth, until its mechanical energy is all converted into thermal energy?