Science Along the Sidewalk
During a neighborhood street fair, a science club sets up two carts near busy sidewalks. The Park Gate cart has sealed pouches of ice. The Metro Plaza cart has bottles of water and small cups of salt. Visitors will compare what happens to the total weight when ice melts and when salt mixes with water.
Each cart has a digital scale on a level, sheltered table. Before each trial, students place an empty tray on the scale and reset its reading to zero. The tray stays on the scale during each measurement. Its weight is not included in the recorded numbers. Students wait for the display to stop changing and record the reading to the nearest gram.
At Park Gate, an adult places ice in a pouch and seals it. Students weigh the closed pouch, including the ice and the pouch itself. They leave it at room temperature until the ice melts. Then they weigh the same closed pouch again. They do not open it or add anything. They check that no water has leaked onto the table.
At Metro Plaza, students first weigh a capped bottle of water. Next, they weigh a cup holding salt. An adult pours all the salt into the bottle and replaces the cap. The students gently swirl the bottle until no salt grains can be seen. They weigh the capped bottle together with the empty salt cup. Nothing is spilled or thrown away.
Each cart completes three trials with different starting amounts. The pouch weights include the pouch and everything inside it. The final mixing weights include the bottle, cap, mixture, and empty cup. The records below show the scale displays. Before comparing a mixing trial's starting and ending weights, students must combine its two starting readings.