I would say that a mass on a spring or a pendulum moves sinusoidally or harmonically (approximately, anyway), not exponentially. And I wouldn’t say that a ball

I would say that a mass on a spring or a pendulum moves sinusoidally or harmonically (approximately, anyway), not exponentially. And I wouldn’t say that a ball falling through the air or sitting on the ground is moving exponentially, either, even if one could get at it via a matrix exponential.