## Tuesday, November 16, 2010

### Period 2 Energy and Systems

Today we are going over the types of energy (gravitational potential, elastic potential, internal, kinetic). We are figuring out what work is being done to these situations:

Person dragged along the ground --> work: thing that is dragging the person
INTERNAL ENERGY system: person, ground, earth

0 J + 5 J = 5 J (started with no energy and gained 5 J of energy)

The ground needs to be in the system because it causes friction on the ground to heat it up. The earth also has to be in the sytem.

Hot air balloon rising into the air --> work: hot air or fire GRAVITATIONAL
system: earth, balloon POTENTIAL

50 J + 10 J (started in the air and increased height by 10 J)

Person on a pogo stick --> work: earth, pogo stick
system: pogo stick ELASTIC ENERGY

I'm not sure about this one but i think it would be: 5 J + 5 J = 10 J because you bounce up and down each time it is not like going down a hill and increasing energy.

You need to have the pogo stick in the system because it wouldnt have springiness (elastic energy) without it.

Car falls off of a cliff --> work: earth system: car KINETIC ENERGY

10 J (driving) + -5 J (falling negative work) = 5 J

I am a little confused on how you would find the equation for something like the pogo stick problem so can anyone tell me what they think it would be? Thanks

EE