Book contents
- Frontmatter
- Contents
- Preface
- Background: what you need to know before you start
- 1 Gravity on Earth:
- 2 And then came Newton
- 3 Satellites
- 4 The Solar System
- 5 Tides and tidal forces
- 6 Interplanetary travel
- 7 Atmospheres
- 8 Gravity in the Sun
- 9 Reaching for the stars
- 10 The colors of stars
- 11 Stars at work
- 12 Birth to death
- 13 Binary stars
- 14 Galaxies
- 15 Physics at speed
- 16 Relating to Einstein
- 17 Spacetime geometry
- 18 Einstein's gravity
- 19 Einstein's recipe
- 20 Neutron stars
- 21 Black holes
- 22 Gravitational waves
- 23 Gravitational lenses
- 24 Cosmology
- 25 The Big Bang
- 26 Einstein's Universe
- 27 Ask the Universe
- Appendix: values of useful constants
- Glossary
- Index
5 - Tides and tidal forces
The real signature of gravity
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Background: what you need to know before you start
- 1 Gravity on Earth:
- 2 And then came Newton
- 3 Satellites
- 4 The Solar System
- 5 Tides and tidal forces
- 6 Interplanetary travel
- 7 Atmospheres
- 8 Gravity in the Sun
- 9 Reaching for the stars
- 10 The colors of stars
- 11 Stars at work
- 12 Birth to death
- 13 Binary stars
- 14 Galaxies
- 15 Physics at speed
- 16 Relating to Einstein
- 17 Spacetime geometry
- 18 Einstein's gravity
- 19 Einstein's recipe
- 20 Neutron stars
- 21 Black holes
- 22 Gravitational waves
- 23 Gravitational lenses
- 24 Cosmology
- 25 The Big Bang
- 26 Einstein's Universe
- 27 Ask the Universe
- Appendix: values of useful constants
- Glossary
- Index
Summary
The tides wash the margins of all the great oceans, regulate the lives of sea urchins and fishermen, power the great bore waves on rivers like the St. John, the Amazon, and the Severn. For most of us the tides are romantic, primeval, poetic. Standing on an ocean beach, we might be impressed by this tangible manifestation of the gravity of the distant rock we call the Moon, but few of us would be led to reflect on how fundamental the tides are to an understanding of gravity itself. But fundamental is the right word. In the modern view, the real signature of gravity, the part of gravity that can't be removed by going into free fall, is the tidal force, whose most spectacular effect on Earth is to raise the ocean tides. In this chapter we will examine this aspect of gravity, starting with the simplest effects first and working our way up to ocean tides and then to tides elsewhere in the Solar System and beyond. We will return again and again in later chapters to the fundamental role of tides. Indeed, many astronomical systems transmit tidal forces as signals right across the Universe, signals that we call gravitational waves.
In this chapter: we study tidal gravitational forces. These are the forces that are not removed in free fall, because they come from non-uniformities in the gravitational acceleration. Their effects are visible all over the Universe, from the ocean tides on the Earth to the disruption of whole galaxies when they get too near to one another. The precise calculation of the tidal effects on Mercury's orbit left a tiny part of Mercury's motion unexplained by Newtonian gravity, its first failure. Einstein's general relativity explained the discrepancy.
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- Information
- Gravity from the Ground UpAn Introductory Guide to Gravity and General Relativity, pp. 39 - 50Publisher: Cambridge University PressPrint publication year: 2003