Quantities and Units PDF

QUANTITIES AND UNITS All the quantities in the world can be categories under one of two groups – base quantities and derived quantities BASE QUANTITIES Base quantities cannot be expressed in terms of other quantities. List of base quantities and their units 1. Time (seconds) 2. Length...

QUANTITIES AND UNITS All the quantities in the world can be categories under one of two groups – base quantities and derived quantities BASE QUANTITIES Base quantities cannot be expressed in terms of other quantities. List of base quantities and their units 1. Time (seconds) 2. Length (metre) 3. Mass (kilogram) 4. Temperature (kelvin) 5. Electric current (ampere) 6. Amount of substance (mol) 7. Luminous Intensity (candela) Derived quantities are expressed in terms of two or more base or derived quantities. *All quantities that do not belong to the list of base quantities are derived quantities The list below shows some derived quantities expressed using other base and derived quantities Force: Force = mass (base) x acceleration (derived) Speed: Speed = Distance (base) / time (base) Momentum: Momentum = mass (base) x velocity (derived) Pressure: Pressure = Force (derived) / Area (derived) UNITS A unit quantifies (gives meaning to) a quantity A unit should never be confused with a symbol The table below shows a clear distinction Quantity Quantity’s Symbol Unit Unit’s Symbol Resistance R Ohm Ω Force F Newton N Charge Q coulomb C Moment p Kilogram metre per second Kg ms-1 RELEVANT QUESTION FROM QUESTION PAPER GRAPHS Graphs serve two purposes in physics/mathematics. Quantity vs Quantity graphs represent the relationship between two quantities. These include force – extension or voltage – current graphs. The two quantities are directly proportional The two quantities are inversely proportional Quantity vs time graphs show how a specific quantity changes over time. While dealing with quantity – time graphs, two factors have to be taken into consideration – 1. How the quantity is changing with time 2. How the rate is changing with time The following are some generic graph shapes that apply to almost any situation, not just motion. *For a quantity – time graph, the gradient represents the rate.