Why does a struck bell keep ringing after you stop touching it?
The strike stores energy in vibrating metal, and the bell bleeds it back out as sound only slowly.
The strike loads the metal with energy
A bell is a stiff, springy hunk of bronze. When the clapper hits it, that one quick blow shoves the metal out of shape for a fraction of a second. The bell wants to snap back, overshoots, snaps back again, and you have a vibration.
Your hand and the clapper are gone in an instant, but the energy they delivered is now sloshing inside the metal itself. Nothing has to keep touching the bell for it to keep moving.
Why it does not stop at once
The bell rings on because it is a very low-loss oscillator. Each vibration only spends a tiny slice of its stored energy, so it takes thousands of cycles to run dry. Engineers call this a high Q factor: bronze is stiff, internally springy, and wastes little energy as heat.
Because only a sliver leaks away per cycle, the loudness fades along a slow exponential curve rather than cutting off. That long tail is the lingering ring.
Touch it and the ring dies
Press a finger to the vibrating rim and the sound vanishes almost instantly. Soft flesh is a poor spring and a good sink; it absorbs the oscillation and turns its energy into heat far faster than the air alone ever could. Damping a bell is easy. Keeping one ringing is the trick the metal does for free.