Can a power failure or forceful shutdown damage hardware?

Can computer hardware suffer damage from forceful shutdowns (holding the power button for five (5) seconds) or power failures?

I believe that normal PC hardware does not suffer from this - after all, it's not much different than what they experience under a standard shutdown. But elsewhere I've read tht another person thought that it could do physical harm to the hard drive and possibly other components as well. He also said that the journaling features of filesystems are useless in face of power failures and were intended to help mitigate damage from system crashes.

I think this is nonsense, but then again I lack the experience and knowledge to say it with certainty.

Answer

In the case of shutdown using the button, no hardware damage is possible (noting that corrupted storage content is not hardware damage).

In the case of power failure, damage is not caused by the sudden loss of power. But it absolutely can be caused by the fluctuations of voltage and current, both up (at extreme levels these are called spikes) and down (brown-outs) that inevitably occur on the line immediately prior to power loss as the power company's equipment fails. These fluctuations can be observed often in your house lighting as it flickers before losing power.

In addition, since voltage fluctuation can sometimes occur during normal operation, without total power loss, a high quality PSU or some kind of power conditioning UPS will help preserve the longevity of your equipment.

Dirty power, or EMI noise on the power line, is also damaging to sensitive electronic equipment - watch where you plug in that treadmill or other large motor device.

Lastly, power fluctuations are more prevalent on low voltage (110 - 120 V) mains than on high voltage, such as 220 - 240 V systems.