Mathematics/Physics
Introduction
To The Number
Line
Sheila
Alexander 
Manley
School 
2935
W. Polk St. 

CHICAGO
IL 60612 

(773)
5346900 
Objectives:
The students will learn how to add and subtract using the number line with positive and negative numbers. The lesson is designed for third through ninth grades.
Materials:
Magnets that stick to the board.
Strategy:
First draw the positive side of the number line on the board. Point out the following; 0 is neither positive nor negative, a positive number is greater than 0, and positive numbers are to the right of 0. Begin by giving sample problems such as (8 + 1 = 9) to solve using the number line. Place the first magnet under the number eight, and then explain that the plus sign is telling you to move in the positive direction once, then place the second magnet where you ended, and that would be your answer (9). Show several examples with simple problems such as the one above. Make sure everybody understands this technique before moving on.
We can also show how to subtract
using the positive number line (8  1),
tell me what number should I place the magnet under?
“Eight “ Why? Because that is the first number in the problem,
then explain that the subtraction sign means to take something away,
therefore
we need to move back one space to the number (7), and
that would be our answer.
We can now give the following rule:
when adding two positive integers, the answer will be positive.
At
this point draw the other half of the number line on the board, this
side of
the number line is for the negative numbers.
The important points regarding the negative numbers are; 0 is neither positive nor negative, a
negative number is less than 0, and
the negative numbers are to the left of zero.
I would proceed by giving examples of adding with negative
numbers. For
example:
^{}7
+ ^{}2 = ^{}9
Place
the first magnet under the number seven (negative), then explain that
the plus
sign is telling us to add two more negative integers, move two steps to
the
left of the number seven and that will give you the correct answer (9).
Give more examples of problems using negative numbers. The rule that applies here is: when
adding two negative integers the answer will be negative.
There
is one more piece to this puzzle and that is learning to subtract using
unlike
signs (positive and negative). For
example:
7  ^{}2 = 7 + 2 = 9.
The rule is: do the opposite of the sign
number
and change everything to positive.
The sign number is the second number in the problem (2);
therefore we would change the subtraction sign to an addition
sign and change the negative two (2) to
a positive two (+2). You
could also answer this problem using
the number line.
We
would begin at the number seven (place the magnet under the number),
the
subtraction sign is telling us to move two steps towards the origin
(which is
zero) but our sign number is telling us to do the opposite of that,
move two
steps further away from the origin beginning at the number seven (+7), and that is how we arrived at the
number (+9) for our answer.
Performance
Assessment:
I will have the class solve several problems
using
the number line. They will answer the
problems on their papers and on the board.
Conclusion:
When you move in the negative direction on the number line, it does not mean that you are going backwards, but simply that you have changed direction.