General Principles 4/10/2019

Objectives To provide an introduction to the basic quantities and idealizations of mechanics. To review the principles for applying the SI system of units. To examine the standard procedures for performing numerical calculations. To present a general guide for problem solving. 4/10/2019

Mechanics: Definition Branch of physical sciences concerned with the state of rest or motion of bodies subjected to forces. 4/10/2019

Engineering Mechanics Solid Mechanics Fluid Mechanics Rigid Bodies Deformable Bodies Statics Dynamics 4/10/2019

Rigid Body Mechanics Statics – Bodies at rest Dynamics – Accelerated motion of bodies 4/10/2019

Basic Quantities Length Time Mass Force meter foot second kilogram slug Force newton pound 4/10/2019

Length Needed to locate the position of a point in space and describe the size of a physical system. 4/10/2019

Time Conceived as a succession of events. Concepts of STATICS are time independent. 4/10/2019

Mass A property of matter by which we can compare the action of one body to another. This property manifests itself as a gravitational attraction between two bodies and provide a qualitative measure of the resistance of matter to a change in velocity. 4/10/2019

Force Generally considered as a push of a pull exerted by one body on another. Interaction occurs when there is direct contact between the bodies. Gravitational, electrical and magnetic forces do not require direct contact. Force is characterized by magnitude, direction and point of application. 4/10/2019

Idealizations Particle - an object having mass but the size is neglected. Rigid Body - a combination of a large number of particles which remain in a fixed position relative to each other, both before and after the application of a force. 4/10/2019

SI Units Modern version of metric system. Base units are length, time and mass, meter (m), second (s), and kilogram (kg) Acceleration of gravity: 4/10/2019

SI Units Force is derived quantity measured in unit called a newton 4/10/2019

Systems of Units Name SI Length Time Mass Force meter (m) second (s) kilogram (kg) newton (N) 4/10/2019

Prefixes for SI units 4/10/2019

Dimensional Homogeneity Each of the terms of an equation must be expressed in the same units. s = v t + 1/2 a t 2 s is position in meters v is velocity in m/s a is acceleration in m/s2 t is time in seconds [m] = [m/s]  [s] + [m/s2]  [s2] = [m] 4/10/2019

Convert 2 km/h to m/s. How many ft/s is this? SOLUTION: Since 1 km = 1000 m and 1 h = 3600 s, the conversion factors are arranged so that a cancellation of units can be applied. Recall that 1 ft = 0.3038 m 4/10/2019

Procedure for Analysis Read the problem carefully and correlate the actual physical situation with the theory studied. Draw necessary diagrams and tables. Apply relevant principles, generally in mathematical form. 4/10/2019

Procedure for Analysis Solve the equations algebraically (without numbers) as far as possible, then obtain a numerical answer. Be sure to use a consistent set of units. Report the answer with no more significant figures than the accuracy of the given data. Decide if answer seems reasonable. Think about what the problem taught you! 4/10/2019