1. Negative Numbers Negative numbers in everyday life

2. Objectives Know that negative numbers are used to measure: temperatures below zero degrees the change in temperature when the temperature falls balance of an overdrawn bank account

3. Temperatures below zero degrees Introductory Information In 1742 Andres Celsius invented a temperature scale based on the freezing and boiling points of pure water. Zero degrees on the celsius scale is the temperature at which pure water freezes. In winter it is possible for the air temperature to become lower than that at which water freezes. That is, when using the celsius scale, it is possible for the temperature to be less than zero!

4. Temperatures below zero degrees It is important, when quoting a temperature close to freezing, to state whether it is above zero or below zero. Above zero is indicated by using positive numbers; three degrees above zero is, in figures, + 3 o Below zero is indicated by using negative numbers; three degrees below zero is, in figures, - 3 o

5. Temperatures below zero degrees A temperature of - 6 o is; A temperature of - 10 o is; One degree below zero is; nine degrees below zero is; six degrees below zero. ten degrees below zero. -1o-1o -9o-9o

6. Change when the temperature falls Over a certain twenty four hour period air temperatures were; 6:00 am 12:00 noon 6:00 pm 20 o 30 o 20 o Between 6:00 am. and 12:00 noon the temperature rose by ten degrees. Between 12.00 noon. and 6:00 p.m. the temperature fell by ten degrees.

7. Change when the temperature falls A temperature rise is a change indicated by using positive numbers; A ten degrees rise is a change of + 3 o A three degrees fall is a change of - 3 o A temperature fall is a change indicated by using negative numbers;

8. Change when the temperature falls A change of - 6 o is; A change of - 10 o is; A fall of one degree is; A fall of nine degrees is; a fall of six degrees. a fall of ten degrees. a change of - 1 o a change of - 9 o

9. Balance of an overdrawn bank account Consider a bank account having a balance of $10.00 If the account holder withdraws $10.00 from the account the balance will be $0.00 The account now has a zero balance. If the account holder makes any further withdrawals the account will become overdrawn. The balance will be less than zero!.

10. Balance of an overdrawn bank account A bank balance which is in credit is indicated by a positive number. A credit balance of ten dollars is, in figures, $ + 10.00 A bank balance which is overdrawn is indicated by a negative number. An overdrawn balance of ten dollars is, in figures, $ - 10.00

11. Balance of an overdrawn bank account A balance of $ - 6.00 is; A balance of $ - 10.00 is; Overdrawn by one dollar is; Overdrawn by nine dollars is; overdrawn by six dollars. overdrawn by ten dollars. a balance of $ - 1.00 a balance of $ - 9.00