What students need to know

• Students know that the weight of an object is equal to the weight of the sum of its parts. This is true in all closed systems.

• Students compare the weight of an object before and after an interaction (e.g., interactions may include tearing, combining, filtering, adding or removing heat, rearranging, cutting, etc.).

What students need to do

• Collaboratively produce data to compare the weight of objects before and after an interaction (e.g, mixing, dissolving) to serve as the basis for evidence, using fair tests in which variables are controlled and the number of trials considered. 

• Students know how to accurately measure and record the weight, and use appropriate tools. 

What students need to be able to answer

• What evidence is there that matter is conserved in this system? (The amounts before and after weigh the same.)

In a closed system, the weight of an object before and after an interaction __________________. (stays the same)

• When matter seems to vanish, the weight __________ (stays the same) because _____________(the substances such as sugar in water, still remain present in a different form)

• What would happen to the weight of a drink if you dissolved 10 grams of sugar into a glass of unsweet tea that originally weighed 411 grams? Would the drink weigh more, less, or the same? How much would it weigh? (it would weigh more as the sugar is present; 421 grams)

Which words students need to know

• substance, interaction, evidence, properties, weight, conservation, vanish, dissolve