What is equilibrium? Well, let's think about it as a state of balance.
And that balance I mean well, balance forces.
Before we get too deep into a definition, let's talk about some examples.
For example, let's consider a ball in a well.
If I release this ball from right here, well we all know what's going to happen.
It's going to roll back and forth and eventually it's going to settle in one spot.
A place where it settles somewhere near here is its equilibrium.
If you disturb the ball from its equilibrium, say by shifting it a bit to the right,
well now it's on a hill and we could do some force decomposition,
and we would see that there's actually a force pointing down the hill.
It's going to tend to restore this object back to its equilibrium.
And this is such an important concept given its own sentence here.
If I'm being specific, I should change the title to stable equilibrium.
This idea that when disturbed the object would try to return to equilibrium
that's the characteristic of what's known as stable.
There is also semi-stable and unstable equilibrium, but we're not going to talk about those today
because this is the sort of equilibrium that gives you the simple harmonic motion
we need for our chronometer.
There's lots of other systems that have this exact same property.
For example, if you have a mass hanging from a spring
Its default state just hanging in equilibrium, but if I pull the mass down,
the spring will exert a force back upwards which tends to restore it to equilibrium.
Likewise with a pendulum or a mass swinging from a rod, its default state, its equilibrium is vertical.
If we displace it from vertical, there will be some component of force
in this case gravity, which tends to restore it.
There is one more key point for simple harmonic motion.
The criteria that must be fulfilled if we're going to get isochronous periodicity that we want,
and this one I want you to complete for me.
So, you could look at this for example as I move this ball further and further up the hill
further from equilibrium, does the force tending to push it back increase, decrease, or stay the same?
Enter your answer here.
