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## Measurement

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**A simple definition of physics is “the science of**measurement”. Measurement Since the formal practice of Science began, Scientists have needed a way to both record & share their findings with the world • World Scientists agreed that a single set of units were needed The System International (SI) was formed • Based on the metric system**Measuring**For a measurement to be useful, it must: Be accurate. Have a unit.**We need to use UNITS in science and everyday life**• Without units numbers are meaningless, from this point any numbers in science should be followed with proper units. • We will use the “MKS” System • meter, kilogram, seconds • The “CGS” System is not used by scientists • Centimeter, Gram, Seconds**Fundamental Units of the SI system**• Length meter (m) • Mass kilogram (kg) • Time second (s) • Temperature Kelvin (K)**Measuring Length**Measuring instruments: Tape measure. Opisometer (for small curves). Trundle wheel (for longer distances). Metre stick. Vernier callipers (for circular objects). The SI Unit of length is the metre (m) (In Junior Science centimetres (cm) & millimetres (mm) can also be used).**Reading measuring instruments correctly**When looking at a measuring instrument (like the metre ruler below) from different angles different readings on the scale can be seen. This is known as a parallax error. • To avoid Parallax error place your eye at 900 (perpendicular) to the scale being read – green option in diagram**Simple Callipers**Callipers can measure the diameter of objects like pipes, beakers, cans, tennis balls, etc. The diagrams show how callipers are used to find the outside (external) and inside (internal) diameter of a beaker. The jaw width on the callipers is measured with a ruler.**Vernier Callipers**These are a more accurate form of the callipers above, They are used to measure small lengths or thicknesses. They can also measure inside and outside diameters. They contain two scales. The first is a fixed main scale measured in centimetres. The second is a smaller scale, called a Vernier scale. The Vernier scale can slide over the main scale.**How to use a Vernier Callipers**• Place the ball to be measured securely between the jaws of the Vernier callipers. • Take the first reading where the zero or first line of the Vernier scale meets the main scale. We can see from the photograph that the diameter of this ball is between 3.2 and 3.3 cm. • For the final decimal place, look closely at the Vernier scale. You must find the first line on the Vernier scale that is directly underneath a line from the main scale. In this case, the line at ‘8’ best satisfies this condition. • Therefore, the diameter of the ball is 3.26 cm.**Opisometers**Opisometers are used to measure the length of curved lines. • To use an opisometer : • Turn the wheel of the opisometer until it sticks to the pointer at the side of the axle. • 2. Carefully roll the opisomeler along the whole length of the line it is measuring. 3. Place the opisometer at the zero of a metre stick. 4. Then roll the opisometer wheel in the opposite direction until it comes back and sticks to the pointer again. 5. Note the reading on the metre stick, where the wheel stops. this is the length of the line.**Trundle Wheel**The trundle wheel is like a very large opisometer. It differs in that it has its own scale marked on it. Trundle wheels are used to measure longer lengths. They are often used to measure curved or straight lines on football pitches or athletic tracks.**Area**The SI Unit of area is square metres (m2) Smaller areas could be measured in square centimetres (cm2) or square millimetres (mm2) The area of a shape is the amount of surface enclosed within its boundary lines.**Measuring the area of a rectangle**To measure the area of a square or rectangle, multiply the length (l) by the width (w). For example, the area of the rectangle on the right is calculated like this: Area = length (l) × width (w) Area = 8.75 cm × 5.2 cm = 45.5 cm2 8.75cm Width (w) 5.2cm Length (l)**Measuring the area of a triangle**The area of the triangle on the right is calculated like this: Area = ½ × base (b) × perpindicular height (h) Area = ½ × 7.5 × 5 = 18.75 cm2 h 5cm b 7.5cm**Volume**To measure volume of a regular cuboid shaped object use formula Volume = length × width × height. Volume = 20 m × 10 m × 8 m Volume = 1600 m2 The volume of an object is the amount of it takes up. The SI Unit of Volume is cubic metre (m3) (Smaller volumes can be measured in cubic centimetres (cm3) or cubic millimetres (mm3))**Volume of Fluids (liquids & gases)**Volume of fluids are usually measured in litres (L) • 1 L = 1000 mL (millilitre) • 1 mL = 1 cm3 → 1 L = 1000 cm3**Instruments to measure volume of liquids**pipette Graduated Cylinder**When Reading Volume of liquids remember to;**Avoid parallax error. Read to meniscus shown below. X X meniscus**Measuring the volume of an irregularly shaped object that**sinks (stone) in water using a measuring cylinder 2 cm3**Measuring the volume of an irregularly shaped object that**sinks (stone) in water using an overflow can Volume of stone 14 cm3**Mass**Mass is the amount of matter (material) in an object. Mass is Measured using a Mass balance. SI Unit of Mass is the kilogram (kg) The mass of an object never changes no matter where the object is in the universe.**To find the mass of a liquid or a gas**Measure the mass of a container (beaker or balloon) Place liquid or gas in container Reread the mass of the container Subtract this mass from the original mass This is the mass of your liquid or gas**Balloon expt. can be misleading**• Weighing an empty and an inflated paper bag or plastic bag will not show any difference. • An inflated balloon is heavier than a deflated one because it contains air at a higher pressure which is therefore denser than the surrounding air. • Link**Time**The SI unit of time is the second (s). (Minutes, hours, days, years, etc. may also be used).**Temperature &Thermometers**The temperature of an object is a measure of how hot or cold the object is. Types of thermometers Mercury and Alcohol Thermometers can be used to measure temperature because the liquids expand when heated**When using mercury or alcohol thermometers avoid**parallax error.**Electronic digital thermometers are used in many homes to**measure body temperature plastic strip thermometer contains heat-sensitive liquid crystals in a plastic strip that change colour to indicate different temperatures. The thermoscan ear thermometer is placed in the patient’s ear. The temperature can be read after just 1 s. Temperature sensors with data-logging equipment are also commonly used in laboratories**Pre fixes used in the SI system. A prefix is often used with**units. It is put in front of the unit.