THE STRENUOUS contemplation of Newton's laws of motion (or, still less, of angular momentum) isn't everyone's idea of a vacation. My own slovenly habit at the seashore, for instance, is to try to drain my skull of any but the most diverting trifles.

But now that Professor James Trefil has set forth his energetic alternative in this clever book, he half persuades me that I've been missing something. The lotus-eating vacation is in danger.

Here is his alternative. When Trefil, a physicist, sees a wave washing up the beach, he doesn't just see a wave. He sees many interesting illustrations of mathematical constants between wave frequencies and lengths, applicable not only to water but to electricity. Tides and sailboats, similarly, lead far beyond the visible world. Even the most routine sights at the seashore suggest thoughts of increasing complexity.

You begin, say, with tides. Soon you're in an engaging discussion of the moon, planets, their orbits, their illustration of the laws of universal gravitation, and even how the observed "perturbations" of planetary orbits can suggest the presence of undiscovered bodies in the solar system. For a bonus, Trefil tells you how the moon was gradually "despun" so that you always, from earth, see only one face of it. Or, turning to sailboats, you are gradually led into an enlightening refresher course on that basic stuff of physics, vectors of force. Or, improbably, Trefil begins by reflecting on the commonplace pleasure of skipping flat stones on water or sand and, before you know it, has insinuated a small course on the mysteries of angular momentum. From there, it's a mere spin of the top to inertial guidance systems, which, linked to computers, keep missiles, spacecraft and advanced aircraft on course, at proper attitudes.

MUCH of it is the sort of thing that used to be studied, and still may be, in college astronomy and high school physics; but it is pleasant to have one's memory so engagingly jogged, and science so amiably sugarcoated.

Along the way, as with most good books of popularized science, one stands to learn a good deal that is completely new. This reviewer learned, for instance, that our days are lengthening (by two milliseconds per century) and that the significantly shorter days of prehistoric times are now verified in oceanic coral deposits. I am not sure I knew, or remembered, that most of the saltiness of seawater comes from upwelling minerals at the various oceanic rifts, rather than from the runoff in rivers. And Professor Trefil has taught me so much about the chemical and physical properties of sand, silt, and clay that a footprint will never again look the same.

Only rarely does Trefil become, to my taste, a bit longwinded (on the subject of waves) or make unnecessarily heavy going of a fairly simple principle (the air foil, as in sails and wings). But maybe I missed a subtlety there. And it is doubtful that a sailor worth his sodium chloride has ever contemplated the familiar impossibility of sailing into the "teeth" of the wind; make that "eye."

But such trifles aside, this is an ingenious and well-written book, albeit one that the world's beach bums may greet with a certain dread. Trefil anticipates the obvious objection that one's enjoyment of nature might be spoiled by an excess of knowledge (we murder to dissect); but his answer, surely correct, is that enjoyment was never decreased by understanding.

No, the deeper worry is the danger of the precedent. Trefil has made, and made well, his point about science at the seashore. But A Scientist at the Seashore intimates the possibility of sequels -- A Scientist in the Kitchen, shall we say, or even A Scientist in the Bedroom? Not everyone will welcome the intrusion of physics into every place of rest and refuge.