Unit 1 Engineering Physics

20 CHAPTER 1. PROPERTIES OF MATTER

Torsion wrench Screw driver

Automobile Suspension

Tightening of a

nut with a wrench

Steam turbine shaft

Figure 1.17: Examples of torsion devices

F

a b

b’

T

T

L

γ a

b

b’

T

T

L

θ c

(a) Shear strain (γ) = <bab’ (b) Angle of twist (θ) =<bcb’

Figure 1.18: Shear strain(“)and twist angle(◊)of a shaft under torsion.

1.7 Torsion pendulum................................

Torsion pendulum is an oscillator for which the restoring reaction is torsion. It consists
of a disk-like mass suspended from a thin rod or wire (Figure1.19). When the mass
is twisted about the axis of the wire, due to its elasticity the wire exerts a torque on
the mass, tending to rotate it back to its original position. If twisted and released, the
mass will rotate back and forth, executing simple harmonic motion (torsional oscillation
or angular oscillation).

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