Kitchen Drop Tests: Speed, Mass and Kinetic Energy

The Cracked Tile

1Last spring, Thandiwe Lindgren's father bumped a cast-iron skillet off the stove while he was stirring a pot of soup. The 2.0 kg pan hit the kitchen floor and cracked a tile. Before the family chose a cushioned mat for the cooking area, Thandiwe, an eighth grader, wanted to find out how much energy a falling object brings to the floor and what that energy depends on.

2An object that is moving has kinetic energy. Her science teacher, Mr. Arvid Mensah, gave her the formula KE = ½ × m × v², where m is the mass in kilograms (kg) and v is the speed in meters per second (m/s). The energy is in joules (J). The v² part means the speed multiplied by itself, so a speed of 3.0 m/s gives 3.0 × 3.0 = 9.0.

3To keep the tests safe, Thandiwe dropped sealed bags of dry food instead of pans or dishes, and every bag landed on a thick old exercise mat. Her father did any drop that started above his shoulders while she stood back. She taped a measuring tape to the side of a cabinet and filmed each drop with the slow-motion setting on a phone. By timing how long each bag took to fall through the last 20 cm, she found its speed just before it reached the mat. She dropped every bag three times and recorded the average speed, rounded to the nearest 0.5 m/s.

4In Test 1, she used one 1.0 kg bag of rice. She dropped it from three places: the bottom pantry shelf, the countertop and the top of the refrigerator. A bag dropped from a higher place was moving faster when it reached the mat. She worked out the kinetic energy for each speed and plotted the results on a graph.

5In Test 2, she dropped four bags with different masses, all from the countertop: a bag of beans, the bag of rice, a bag of sugar and a bag of flour. She recorded the results in a table. Her younger brother, Elias, watched the sugar bag land with a loud thud. "Heavy things fall faster," he said. "That's why the sugar hit so hard."