For example, you want to imagine natural frequency

of your car when car is moving up and down.

What do you do? You just push your car using

your feet giving unit displacement

or some displacement and then let it go, it'll oscillate.

If you measure the frequency,

then you can measure

the natural frequency of your car in this direction.

You want to measure

the natural frequency of your car in this direction?

You push, I don't know whether you can do it,

but you push and then let it go,

oscillate and measure your frequency,

then you can measure natural frequency of your car.

Or you can also measure stiffness of your suspension,

for example, k if you know the mass of your car.

Now, you measure the frequency and if you

know the mass of your car,

you can measure the suspension stiffness of your car.

So, simple expression, but

has many practical implication.