TP To identify base and derived quantities and

TP To identify base and derived quantities and their units.

THE SI SYSTEM OF UNITS The base units have been accepted and adopted by scientists worldwide. They are known as the SI UNITS or Systeme Internationale de units International systems of units.

BASE UNITS Units from which all other units can be obtained or derived from. BASE QUANTITY BASE UNIT SI SYMBOL 1. Length metres m 2. mass kilogram Kg 3 Time seconds s 4. Temperature Kelvin K 5. Electric current Amperes A 6. Amount of substance Moles 7. Luminous intensity Candela mol cd

DERIVED UNITS • These are units obtained by combining two or more base units. • Examples of derived units: 1. Units of speed: m/s, mph 2. Units of acceleration: m/s 2 3. Units of Energy: J or NM

Dimension 1. 2 Velocity speed Volume 3. density 4. acceleration 5 Force 6 Energy 7 Power Formula Derived Unit Alternative unit ms-1 V = lwh m 3 Kgm-3 ms-2 F = ma E = Fxd= mad Kgms-2 Newton(N) Kgm 2 s-2 Joule(J) Kgm 2 s-3 Watts(W)

Dimension Formula Derived Unit Alternative unit 8. Pressure Nm-2 Pascal 9 Frequency s-1 Hertz (Hz) 10 Charge As Coulombs(C) 11 Voltage kgm 2 s-3 A-1 Volts(V) 12 Resistance kgm 2 s-3 A-2 Ohms( ) 13 Energy Kgm 2 s-2 Joule(J) 14 Power Kgm 2 s-3 Watts(W) Q = It E = Fxd (Pa)

TP Recap. Working with base units.

Sample questions From Past papers MJ 2002 P 1

MJ 2010 P 1

TP • Recap. • Derived units from a graph(Units of a gradient. • Prefixes.

UNITS OF A GRADIENT/SLOPE

Name PREFIXES Symbol Scaling factor Common example Tera T 1012 Large computer harddrives can be terabytes in size. Giga G 109 Computer memories are measured in gigabytes. Mega M 106 A power station may have an output of 600 MW (megawatts). Kilo k 103 Mass is often measured in kilogrammes Deci d 10 -1 Fluids are sometimes measured in decilitres Centi c 10 -2 Distances are measured in centimetres Milli m 10 -3 Short time is sometimes measured in milliseconds. Micro µ 10 -6 micrometres are often used to measure wavelengths of electromagnetic waves. Nano n 10 -9 nanometres are used to measure atomic spacing. Pico p 10 -12 picometres used to measure atomic radii.

Convert to SI units 1. 24. 5 km 2. 700 nm 3. 0. 52 A 4. 300 m. A 5. 0. 12 pm 6. 420 Mkg.

TP • Recap. • Homogeneous equations consists of an equation with same units on both sides of the equation.

HOMOGENEOUS EQUATIONS • An equation with same units on both sides of the equation. 15 kg +5 kg =20 m 15 kg +5 kg =20 kg Same units, homogeneous Units do not agree, non-homogeneous Show that the equation F=ma is homogeneous. Note: F =N =kgms-2. M=kg a= ms-2 F= ma kgms-2 =kg x ms-2 = kgms-2 Same units, homogeneous

Show that the equation E=1/2 mv 2 is homogeneous Note: E=Joule =kgm 2 s-2. M=kg m= ms-1 Note: P=Pa =NM-2 =kgm-1 s-2 F= N= kgms-2 A= m 2 E= 1/2 mv 2 kgm 2 s-2 =kg x (ms-1)2 = kgm 2 s-2 Same units, homogeneous

Show that the equation the following equations are homogeneous. 1. P=hdg 3. E=QV 4. W= Fd