IGCSE PHYSICSGENERAL PHYSICS:

MEASUREMENTS

Main Points to be studied in this sectionMeasurements• Use and describe the use of rules and measuring cylinders to calculate a length or a volume

• Use and describe the use of a mechanical method for the measurement of a small distance (including use of a micrometer screw gauge)

• Use and describe the use of clocks and devices for measuring an interval of time.

• Measure and describe how to measure a short interval of time (including the period of a pendulum)

• Show familiarity with the idea of the mass of a body• State that weight is a force• Demonstrate understanding that weights (and hence masses) may be compared using a balance• Describe an experiment to determine the density of a liquid and of a regularly shaped solid and make the necessary calculation• Describe the determination of the density of an irregularly shaped solid by the method of displacement, and make the necessary calculation

(Cambridge IGCSE Physics ….Syllabus 2014)

• PHYSICAL QUANTITIES• LENGTH• TIME• MASS• VOLUME• DENSITY

PHYSICAL QUANTITIESA physical quantity is a property of an object

that can be measured with a measuring instrument.

A physical quantity is usually expressed as “a magnitude (numerical value) and a physical

unit or more”BASIC SI (INTERNATIONAL SYSTEM UNITS)

QUANTITY SI UNIT SYMBOL DEVICELENGTH Meter m Metre ruleMASS kilogram kg BalanceTIME seconds s stopwatch

Length is “the distance between two points in a space”.

• A rule (ruler) is used to measure length for distances between1mm and 1meter• cm and mm scale•Must touch the object measured• zero on ruler must line up with end of object• read with eye directly over scale to avoid parallax error

A student uses a ruler to measure the length and the width of a small rectangular metal plate. What is the area of the plate?

MICROMETER SCREW GAUGE

• Used to measure very small distances up to .01mm

Determination of the diameter 'd' of a wire• Place the wire between the anvil and spindle end as indicated inthe diagram.• Rotate the thimble until the wire is firmly held between the anviland the spindle.• The ratchet is provided to avoid excessive pressure on the wire. Itprevents the spindle from further movement - squashing the wire

3530

CALLIPERS• have a sliding scale that measures to 0.1mm• object placed in jaws, and callipers closed to just touch it.

TIME• Interval of time is measured using clocks• To find the amount of time it takes a pendulum to make a spin,time ~25 circles and then divide by the same number as thenumber of circles.

Mass is the amount of material that a body contains.Weight is the force of gravity acting on a mass.

VOLUME• To find out volume of regular object, use mathematical formula• To find out volume of irregular object, put object into measuringcylinder with water. When object added, it displaces water,making water level rise. Measure this rise. This is the volume.

DENSITY is the mass of unit volume

•In SI density measured in kg/m3

But can be measured also in g/cm3

Density (d) = mass (m) / volume (V)

At constant massThe density is inversely proportional with volume of the substance.d  inversely proportional to V

At constant volumeThe density is directly proportional with mass of the substance

Notes:     i.        Density of water at 4 0C   is 1000 kg/m3 = 1 g/cm3.

    ii.        Density doesn’t depend on the volume (how big) of the body only; it depends on both its volume and its mass.

   iii.        Density changes with temperature but the density of water is a very exceptional with heat change.

   iv.        Densities of gases depend on their pressure too.

    v.        The less dense float over the surface of the denser.

   vi.        The denser will sink or goes down.