This study investigates the structural intensity and the force distribution function as tools to study vibrating plates. A laser Doppler vibrometer is used in measuring the plate normal velocity for the calculation of the structural intensity and the force distribution function. Several examples show the possibility of locating sources and studying the influence of ribs and damping material attached to the plate surface;There have been many studies on structural intensity. This thesis shows that the differences between two commonly used formulations are the assumptions that are used in deriving the formulas;The force distribution function is introduced in this thesis as an additional tool for source location. From Mindlin's plate motion equation, a force distribution function is solved for based on the measured plate normal velocity (or displacement). It is shown that the force distribution is an effective tool to locate sources;A large part of the dissertation research focused on implementing the experimental determination of the structural intensity and the force distribution function. Since the calculations are implemented in wavenumber domain by Fast Fourier Transform (FFT), signal processing techniques such as windowing and filtering are needed to get reasonable results. The influence of windowing and filtering on the calculation of the structural intensity and force distribution function is studied;The rib and damping material that are attached to plates influence the plate vibration and the energy transmission in the plates. Results show that the rib absorbs the vibrational energy when the vibration waves pass through it. A constraint force is applied by the rib to the plate that restricts the plate vibration. Results also show that the damping material is more effective in absorbing bending and shearing vibration energies than in absorbing twisting energy, and that the damping material does not apply a normal force to the plate.