Work and energy

Take g = 10 N/kg

To high school students, work and energy are abstract and their relationship is not easy to be grasped. In classroom, I have used the following diagram to make things concrete.

Water: energy

Gauge reading: work done

The gauges G1, G2 and G3 are installed to record the amount of water passing through. The readings on these gauges correspond to works dones by the relevant forces. Work is not a kind of energy, it just measures the amount of energy transferred during a process.

"Work done by friction" is negative, while "work done against friction" is positive; their magnitudes are the same.