Energy bar chart
Also called Energy bar graph
A diagram showing one bar per type of energy stored in a chosen system at one instant, all drawn to a shared scale so that snapshots taken at different instants can be compared. AP Physics 1 asks students to draw them on the free-response section.
One system, one instant, one bar per energy type. Draw a second chart for a later instant and the comparison between them is the physics.
The CED treats these as an examinable representation rather than a teaching aid. Science Practice 1 lists energy bar charts among the representations students create, and the sample free-response set makes Question 2, Translation Between Representations, a block-on-a-spring problem whose first part is drawing them.
The CED gives four drawing rules with that question:
- Positive energy values go above the zero-energy line and negative values below it.
- Shaded regions start at the dashed line representing zero energy.
- An energy equal to zero is represented with a distinct line on the zero-energy line, not left blank.
- The relative height of each shaded region reflects the magnitude of that energy, consistent with the scale shown.
The third rule is the one that costs marks. A blank column reads as "I did not answer", while a flat line on the axis reads as "this energy is zero", and only the second is a claim.
The chart is only as honest as the system boundary. Which bars exist at all is decided by what you enclose. Put the block and the spring inside and there is a spring potential energy bar; leave the spring outside and the same interaction has to appear as external work instead. Whether the bars sum to the same total across your snapshots is exactly the mechanical energy question, and it has conditions.
Setting up and solving the balance those charts represent is the job of the conservation of energy guide.