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1.When a pendulum is kept in a car which is sliding down, then
    T= 2 [L / gcos  ] where  is angle of inclination.  
2.if a simple pendulum oscillates in a non-viscous liquid of density ,then its time  
   period is T=2 [ L / ( 1 - /  )  ].
3.If the mass m attached to a spring oscillates in a non-viscous liquid of density ,
   then its time period is given by T= 2 [ m/k (1- / )  ].=density of mass  
    suspended
4.If the time period of one spring is T_1, and that of second spring is  T_2,   and if they  are connected in series,then T_series = T₁ ² + T₂ ²  and if they are connected in 
    parallel T_parallel =T₁ T₂ / [T₁ ² + T₂ ²  ].
5.In the case of a balanced wheel or torsional pendulum,
    T=2   [ I / C ]. where I = moment of inertia, C=torsional constant=restoring 
     torque per unit length.
6. When a ball of mass m is made to oscillate in the neck of an air chamber having volume V and neck area A, then T=2 [ mV / pA² ].
7. If a person sitting on an oscillating swing stands up , the time period of the swing decreases.