1. PHYSICS
Applied Mechanics

2. Applied Mechanics

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

8. 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

10. stretch

11. release

12. But this formula is only valid when force is constantx
force
Work done = force  distance
But this formula is only valid when force is constant

13. 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

14. 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

15. 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

17. Gravitational force
Gravitational force

18. Electric force

21. Electromagnetic force

22. 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

23. 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