PHYSICS Applied Mechanics

Applied Mechanics

Deformation 1 N 1 N 1 cm 2 cm extension Hooke’s law: force  extension

Original unstretched length force doubled  extension doubled Quick Check 1 A spring is initially 5 m long. When a force is applied to stretch it, its length increases to 7 m. When the force is doubled, its length is now A 9 m B 10 m C 11 m D 14 m extension = 7 – 5 = 2 m force doubled  extension doubled  new extension = 4 m

stretch

release

But this formula is only valid when force is constant x force Work done = force  distance But this formula is only valid when force is constant

This formula is only valid in the special case where speed is constant Distance = speed  time General case formula: Distance = area under speed-time graph speed time Distance travelled = area under speed-time graph s = vt v speed time t Distance travelled = area under speed-time graph s = ½(u+v)t v u t

This formula is only valid in the special case where force is constant Work done = force  distance General case formula: Work done = area under force-distance graph force distance Work done = area under force-distance graph W = Fx F force distance x Work done = area under force-distance graph s = ½Fx F x

Energy stored in a deformed material = work done = area under force- extension graph = ½Fx or ½kx2 force F extension x Hooke’s law: F = kx

Gravitational force Gravitational force

Electric force

Electromagnetic force

pressure increases with depth liquid / gas Pressure in a fluid At sea level, pressure = patm h1 p1 = patm + gh1 pressure increases with depth h2 p2 = patm + gh2 p = gh

Quick Check One day, you walk on the sea bed 1 km below sea level. Your lung would be how many times the original size? [patm = 10 m water] A 100 times B half C 10% D 1% of original size At 1 km, gh = 100 patm Total pressure = 101 patm So volume = 1/101  orig. volume