In this KS3 lesson, links are made to the science topic of electricity to help learners understand adding and subtracting directed (positive and negative) numbers.
Lots of learners have heard that ‘two minuses make a plus’ but may not apply this rule correctly or have much sense of when or why it is the case.
Students often carry out calculations with negative numbers by following poorly-grasped rules. Electric charge provides a meaningful context for understanding.
Directed numbers learning objective
- Learn about adding and subtracting directed (positive and negative) numbers
Starter activity
Q) Do you think that negative numbers exist? Why / why not?
Learners could discuss where they have come across negative numbers, such as with cold temperatures in Celsius. But does this mean they ‘exist’? Or are they just a human invention?
Have they always been there ‘on the number line’, waiting to be discovered? People take different views and these questions might help learners to begin to develop their ‘philosophy of mathematics’.
Colin Foster is a Senior Research Fellow in mathematics education in the School of Education at the University of Nottingham. He has written many books and articles for mathematics teachers. Browse more KS3 maths resources.
