28 lines
1.5 KiB
Markdown
28 lines
1.5 KiB
Markdown
[[Work Energy and Power]]
|
||
|
||
# SUMMARY
|
||
* System of one object can only have KE.
|
||
* Mechanical energy is just KE + PE.
|
||
* If work = 0 and no no conservative forces then ME = 0
|
||
* If work is done then systems total energy changes
|
||
* Choice of system boundary decides if an interaction is internal or external (no shit)
|
||
* Nonconservative forces like friction or air resistance can dissipate mechanical energy as thermal energy or sound.
|
||
|
||
## Mechanical Energy Components
|
||
* Kinetic energy is energy of movement
|
||
* Potential energy is energy due to position or config
|
||
* Total ME stays the same when only conservative forces act inside the system
|
||
|
||
By choosing the system carefully, you can set up systems where even if things in the system change no energy exits of enters, called Constant Energy Systems.
|
||
|
||
When a system energy changes, that change matches the change across the system boundary. Energy entering increases total energy, energy leaving decreases it, and net change equals sum of in and out.
|
||
|
||
## System Selection and Energy Changes
|
||
|
||
|Comparison|Falling ball as system|Ball–Earth system|
|
||
|---|---|---|
|
||
|System contents|Ball only|Ball and Earth|
|
||
|Gravity|External interaction; does work on the ball|Internal interaction|
|
||
|Gravitational potential energy|Not included|Included|
|
||
|Energy equation|ΔK=WgravityΔK=Wgravity|Ki+Ug,i=Kf+Ug,fKi+Ug,i=Kf+Ug,f|
|
||
|Mechanical energy conserved when air resistance is negligible?|No; the ball’s kinetic energy changes as energy transfers into the system|Yes; energy converts between kinetic and gravitational potential energy| |