# Physics on the go Materials Section 2

This covers Viscosity, Behaviour of Solids and Flow

HideShow resource information
• Created by: Edward
• Created on: 27-12-12 15:33
• Materials Section 2
• Behaviour of solids
• Brittle materials
• Break suddenly without deforming plastically
• Ductile materials
• Shows plastic deformation
• The cross sectional area decreases before it breaks, ductile yielding
• Can change shape without losing strength
• Tough Materials
• Can withstand sudden impact forces without breaking
• Can be very strong and withstand great stress before breaking
• Examples include rubber, steel or kevlar
• Not brittle
• Hard materials
• Resists plastic deformation, not just from tensile stress but also from dents and scratches
• Example - Diamond
• Malleable materials
• Show large plastic deformation without breaking
• Not brittle, though not necessarily tough
• Can be reshaped without fracturing
• May lose strength
• Stiff materials
• High resistance to bending and scratching
• Llimit of proprtionality
• After this the graph starts to bend, stress and strain are no longer proportional to each other
• Elastic limit
• The point where the material starts to behave plastically
• Yield point
• The stress beyond which the material becomes plastic
• Flow
• Laminar flow
• Velocity of the flow is constant over time
• All fluid elements flow in the same direction
• Usually occurs when fluid is flowing slowly
• Turbulent flow
• Velocity of the flow varies with time
• Fluid elements get mixed up
• Fluid often  flows around miniature whirlpools called Eddy currents
• Viscosity
• Viscosity of a fluid changes with temperature
• Viscosity decreases as temperature increases
• Viscous drag
• The friction between the surface of the object and the fluid
• Stokes' Law
• Viscous drag
• The friction between the surface of the object and the fluid
• F=6(pi)nrv
• n=viscosity of the fluid (Nsm^-2)
• r=radius of the object (m)
• v=the speed the object is moving at (ms^-1)
• Upthrust
• Weight of fluid displaced
• Weight=upthrust +viscous drag