A cart rolls from the top of a ramp to the floor, faster every moment.
Its energy keeps moving between stores as it goes. Keeping track of that in sentences gets long, fast.
How do you see, at a glance, where the energy sits at each moment?
Here are three moments of the cart's roll, drawn side by side.
This drawing is an energy bar chart. Each group is one snapshot: a moment of the motion, frozen.
Within a snapshot there is one bar per store: kinetic energy, gravitational potential energy, and thermal energy, each read in joules.
Read the release snapshot: KE 20 J, GPE 80 J, thermal 0 J. Read the bottom snapshot: KE 100 J, GPE 0 J, thermal 0 J.
The thermal bar sits at 0 J the whole way here: this ramp is frictionless, so no energy has been converted to thermal energy.
On the chart above, how much of the cart's GPE has become KE by the halfway snapshot?
Read the GPE bar at both snapshots:
at release it reads 80 J; at the halfway snapshot it reads 40 J.
The drop is 80 - 40 = 40: that energy left the gravitational store.
The KE bar confirms it: 20 J to 60 J, a rise of 40 J.
40 J of GPE has become KE by the halfway snapshot.
The chart shows a sled's run as three snapshots. At which snapshot is the sled's kinetic energy largest?
The chart shows a wagon's roll at two snapshots. How much GPE has become KE between the start and the partway snapshot? Enter your answer in J.
On a rough ramp a thermal bar grows from snapshot to snapshot. The chart carries that story just as plainly.
A second chart shows the same cart on a rough ramp. Its bottom snapshot reads KE 85 J, GPE 0 J, thermal 15 J. How much mechanical energy has been converted to thermal energy by the bottom?
The thermal bar is the record of what left the mechanical stores.
At the bottom it reads 15 J.
15 J of mechanical energy has been converted to thermal energy.
The chart shows a crate's slide down a chute as three snapshots. At which snapshot does the chart first show thermal energy?
The chart shows a ball's roll as four snapshots. At which snapshot has ALL of the ball's GPE become KE?
The chart shows one snapshot of a cart partway along a track. Enter the cart's total mechanical energy at that snapshot in J.
The chart shows a toboggan's run at the halfway marker and at the end. Between those two snapshots, how much MORE mechanical energy was converted to thermal energy? Enter your answer in J.