Objectives
Students should be able to associate moves that preserve balance in a mobile with moves that preserve equivalence of two expressions and determine solutions that can be converted to the form ax = b and x + a = c.
Vocabulary
expression
equation
variable
solution
identity
Students understand how mapping a balanced mobile to an equation provides a foundation for reasoning about strategies for solving equations.
Some students may reason about the numerical value for each expression in an equation and how they must be the same, while others may reason by identifying numbers that make the mobile unbalanced and in which direction.
If 3c + b = 2b and b = 18 what is c?
Answer: c = 6
Mobiles can be used as a visual/physical model to leverage student reasoning about an equation involving two variable expressions in terms of balance between weights on mobiles.
Students reason about the values of weights on mobiles and use balance to model solution preserving moves algebraically.
Encourage students to use the way the mobile behaves to reason about the values of weights on the mobile and relate that to the values of variables in an equation.
