Ask students to look for variables as they watch Futures Channel Movie #1001 Solar Powered Cars. After the movie, ask students to work in pairs to list as many variables as possible in a few minutes. Discuss the answers, and elicit or suggest the variables of vehicle weight and driver weight. Discuss why it would be important to be able to compute the total weight (because it takes more power to accelerate a heavier vehicle). Then ask students to work in pairs to answer this question: “If the vehicle weight is 240 pounds, and the weight of the driver is a variable which we indicate with the letter d, how would I write down the total weight of vehicle and driver?” Discuss the fact that the answer is not a number, because you don’t know the driver’s weight so you cannot actually add it to the vehicle weight. But there is a way to write down the total weight. Ask students to work in pairs on this and discuss results to agreement that you can write down the total weight as 240 + d.
Tell students that there are many times in mathematics when you write combinations of variables and numbers like this, and that such combinations are called expressions. (Definition of expression: "a combination of variables, numbers and operations that represents a quantity*.) Tell students they are going to learn more about how to create and work with expressions in this chapter.
*Strictly speaking, an expression can also represent a set of quantities, as in a matrix. But the simpler definition should be adequate for this level of work. |
