A pendulum with a length of 1 meter has a period of about 2 seconds (so it takes about 1 second to swing across an arc). This means that there is a relationship between the gravitational field (g) and Pi.

Do pendulums swing forever?

No pendulum can swing forever because the system loses energy on account of friction. That's why a grandfather clock has to be rewound every few days, to inject a little energy back into the system.

What affects the time of a pendulum swing?

The only things that affect the period of a simple pendulum are its length and the acceleration due to gravity. The period is completely independent of other factors, such as mass.