The mass of the pendulum bob was determined on an electronic scale and

[alicia113]

You start with an amount of energy.
You mechanism consumes an amount of energy in operating that does not go towards the desired behaviour. This represents a loss of energy.

The efficiency is calculated from these.

You have to decide what the desired behaviour is from your pendulum. You will need to come up with some kind of energy conversion or energy flow statement so you can identify the loss of energy. You don't need to know what is causing the loss only that it has taken place.

How did you get that. I know it's

Energy output
------------------ x100
Energy input

 

[PeterO]

How did you get that. I know it's

Energy output
------------------ x100
Energy input

Here your energy input is the amount of [potential] energy you begin with, while the energy output equals the amount of kinetic energy you have at the bottom of the swing [plus any potential energy you may have left - which depends on where you chose to define the zero of potential energy]

 

[alicia113]

Bottom of swing?

 

[pgardn]

This is part of a huge problem of trying to complete a physics class online without any teacher.

If I had you right in front of me we could easily get this done in 5 min., provided that you understood the conservation of gravitational potential energy and kinetic energy and setting up your experiment so that the lowest level the mass reaches would be your zero pot. energy level to make it easier...



Now in this simple video YOUR final position will not be as large is A is. In other words height A will be smaller than height C because of friction.

So if you actually did this could you measure C from a lowpoint of B, and A from a low point of B?

Then could you actually do the math to determine how much energy was "lost" turned into heat energy. Thats where efficiency comes in. Your pendulum will not swing all the way back up if you let go from rest. It will not swing all the way back up to the same height, C, from where it started.

So equations: Max pot energy - final pot. energy = heat energy

Or heat energy + final pot. energy = Max pot. energy

Now you got input (max pot energy; point C) and output (final pot. energy; point A in video but its not going to go all the way back up as in the idealistic video...

Alicia one day you are on electricity and the next day on mechanics, you are whizzing through this stuff without a complete understanding. I understand you probably just want to get this over with, I just hope you don't have some final exam you have to do on your own.

Sorry for the inuput, its not meant to be mean. Its just physics is not rote stuff. You got to think about the ideas as well as the math. Its like the math problems in the last part of the chapter that are applied mathematics. The one many kids hate doing because its difficult.

 

[PeterO]

Bottom of swing?

Bottom of the swing refers to the lowest point of the swing.
Sorry about the delay in answering, but I am in Australia in a different time zone to you I expect - and I went to bed.