📊 Units & Variables Mini-Lab

Teacher models how energy can be measured in joules, calories, BTUs, and kilowatt-hours and demonstrates a brief comparison of heating 50 g vs. 100 g of water with the same heat source. Students identify independent, dependent, and controlled variables and discuss how mass affects temperature change. A short guided conversion example (J ↔ calories) connects units to real contexts like food labels and electric bills.