Chapter OutlineMechanicsFundamental ConceptsUnits of MeasurementThe International System of UnitsNumerical Calculations

1.1 MechanicsMechanics can be divided into 3 branches:- Rigid-body Mechanics- Deformable-body Mechanics- Fluid Mechanics

Rigid-body Mechanics deals with - Statics - Dynamics

1.1 MechanicsStatics Equilibrium of bodiesAt restMove with constant velocity

Dynamics Accelerated motion of bodies

1.2 Fundamentals ConceptsBasic QuantitiesLength - locate the position of a point in spaceMass - measure of a quantity of matterTime - succession of eventsForce - a push or pull exerted by one body on another

1.2 Fundamentals ConceptsIdealizationsParticles - has a mass and size can be neglected

Rigid Body - a combination of a large number of particles

Concentrated Force - the effect of a loading

1.3 Units of MeasurementSI UnitsStands for Systme International dUnits (French)SI system specifies length in meters (m), time in seconds (s) and mass in kilograms (kg)Force unit, Newton (N), is derived from F = ma

1.3 Units of Measurement

NameLengthTimeMassForceInternational Systems of Units (SI)Meter (m)Second (s)Kilogram (kg)Newton (N)

1.3 Units of MeasurementAt the standard location, g = 9.806 65 m/s2For calculations, we use g = 9.81 m/s2Thus, W = mg(g = 9.81m/s2)Hence, a body of mass 1 kg has a weight of 9.81 N, a 2 kg body weighs 19.62 N

1.4 The International System of UnitsPrefixesFor a very large or small numerical quantity, units can be modified by using a prefix

Each represent a multiple or sub-multiple of a unitEg: 4,000,000 N = 4000 kN (kilo-newton) = 4 MN (mega- newton) 0.005m = 5 mm (milli-meter)

1.4 The International System of Units

1.5 Numerical CalculationsDimensional HomogeneityEach term must be expressed in the same unitsRegardless of how the equation is evaluated, it maintains its dimensional homogeneityAll terms can be replaced by a consistent set of units

1.5 Numerical CalculationsSignificant FiguresAccuracy of a number is specified by the number of significant figures it containsA significant figure is any digit including zero e.g. 5604 and 34.52 have four significant numbersWhen numbers begin or end with zero, we make use of prefixes to clarify the number of significant figures e.g. 400 as one significant figure would be 0.4(103)

Copyright 2010 Pearson Education South Asia Pte Ltd1.5 Numerical CalculationsRounding Off NumbersAccuracy obtained would never be better than the accuracy of the problem dataCalculators or computers involve more figures in the answer than the number of significant figures in the dataCalculated results should always be rounded off to an appropriate number of significant figures

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Copyright 2010 Pearson Education South Asia Pte Ltd1.5 Numerical CalculationsCalculations Retain a greater number of digits for accuracyWork out computations so that numbers that are approximately equal Round off final answers to three significant figures

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Copyright 2010 Pearson Education South Asia Pte LtdExampleConvert to 2 km/h to m/s.

Solution

Remember to round off the final answer to three significant figures.

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Copyright 2010 Pearson Education South Asia Pte LtdQUIZ1. The subject of mechanics deals with what happens to a body when ______ is / are applied to it. A) magnetic field B) heat C) forces D) neutrons E) lasers

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Copyright 2010 Pearson Education South Asia Pte LtdQUIZ2. For a statics problem your calculations show the final answer as 12345.6 N. What will you write as your final answer? A) 12345.6 N B) 12.3456 kN C) 12 kN D) 12.3 kN E) 123 kN

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