tides

Question 1

what is a flood current?

Answer 1

As the tide rises, water moves towards the shore. This is called a flood current. As the tide rises, water moves towards the shore. This is called a flood current.

Question 2

what causes tides?

Answer 2

• Tides are caused by the gravitational forces exerted on the earth by celestial bodies in direct proportion to their mass

Question 3

what is the difference in mass of the sun and moon?

Answer 3

The sun has 27 million times the mass of the moon. One might expect it to be dominant tide producing force.

Question 4

why has the sun got less impact than the moon on tides?

Answer 4

However, the gravitational force exerted by a celestial body decreases rapidly as the distance from the earth increases.

Question 5

what is the gravitational force equation?

Answer 5

F= Gm1M2 / d^2. F is the gravitational force. M1 and M2 are the masses of the 2 objects. D is the distance between the 2 objects. G is the universal gravitational constant.

Question 6

why does the moon have a stronger effect than the sun?

Answer 6

• However, although the sun to earth is larger than moon-earth, the tidal forces varies with the inverse CUBE of distance, and the moon is much closer to the earth, so the moon has a stronger effect on the tide than the sun.

Question 7

how are the tidal forces produced?

Answer 7

• The tidal forces aren’t produced by the absolute pull of gravity exerted by the sun and the moon, but by the differences in the gravitational fields produced by the 2 bodies across the earths surfaces.

Question 8

how does the moons distance to the earth cause stronger forces?

Answer 8

Because the moon is so much closer to the earth than the sun, it’s gravitational force varies much more strongly over the surface of the earth than the gravitational force field of the sun.

Question 9

what do the tidal forces depend on?

Answer 9

• These tidal forces, depend on the inverse cube of distance. This is why tidal forces on earth from the sun are so much smaller than those on the moon.

Question 10

what is the net effect percentage of the moon and the sun?

Answer 10

• The net effect is that the moon contributes about 70% to the tides, while the sun contributes 30% on average.

Question 11

why dont small bodies of water have tides?

Answer 11

• In smaller bodies such as lakes, swimming pools, gravitational differences over small distances are so slight, they have a negligible affect.

Question 12

what are atmospheric tides?

Answer 12

• As well as the oceanic tides, there are atmospheric tides and terrestrial tides, affecting the solid earth. Atmospheric tides are negligible for every day phenomena, drowned by weather and solar thermal tides. The amplitude of terrestrial tides can reach about 55 cm at the equator.

Question 13

why must the planets be constrained in their orbit?

Answer 13

• As 2 planetary bodies orbit each other, they must be constrained in their orbit by a centripetal force that prevents each from flying off in a straight line.

Question 14

what is the centripetal force?

Answer 14

• The centripetal force is supplied by the gravitational attraction between them.

Question 15

why is the centripetal force needed to maintain the planets in orbit?

Answer 15

• Because every part of each body rotates through an orbital path of the same radius, the centripetal force required to maintain the bodies in orbit, is the same at all points and on each of the bodies.

Question 16

how much more in percentage is the moons gravitational pull than the earths?

Answer 16

• The moons gravitational attraction is about 3% grater at the earths surface nearest the moon.
ween these points. The bulge moves around the earth as the earth rotates and the earth and the moon rotate around each other.

Question 17

why is the moons gravitational pull greater than the earths?

Answer 17

• Because the centripetal force is the same at all points, there is a net excess gravitational force on the side of the earths nearest the moon, and a net deficit of gravitational force on the side farthest from the moon. This is called the tidal poll or tide-generating force.
in a ring around the earths halfway bet

Question 18

how does the earths gravity allow water to not be pulled towards the sun?

Answer 18

• At the point of the earths surface nearest the moon, there is a slight tidal pull. Water is pulled upwards towards the moon at this point. However, the earths gravity, which is very strong, acts directly opposite the tidal pull at this location.

Question 19

what is the tidal pull component?

Answer 19

• At every point except directly under the moon and exactly on the other side of the earth, the tidal pull has a component that acts parallel to the earths surface. This component of tidal pull cannot be compensated by the earths gravity and therefore causes the water to flow in the direction of the force.

Question 20

what is the net result of the tidal forces?

Answer 20

• The net result of the tidal forces actin on the earths oceans in to move water towards points nearest the moon and farthest from the moon. This movement creates bulges of elevated water surfaces at these points, and a depression of the water surface

Question 21

why are there 2 low and high tides a day?

Answer 21

• The earth rotates on its axis once every 24 hours in the same direction. In one rotation (one day), a point on earth travels from an area of high tide (where there is a force pulling water outwards), through an area of low tide, through an area of high tide again (the opposite pull), and through another area of low tide, before it returns to the point of origin at high tide. This results in 2 high tides and 2 low tides in a day: semidiurnal tides.

Question 22

whats the difference between the moon-earth system and the earth day?

Answer 22

• The earth spins once on its axis every 24 hours. But the earth-moon system revolves every 27.3 days.

Question 23

why does the moon move forwards a little in its orbit when the earth rotates?

Answer 23

• By the time the earth has made one complete rotation, the moon has moved forwards a little in its orbit.

Question 24

how much does the earth spin every 4 minutes? therefore- work out how long it takes for the moon to elapse.

Answer 24

• The earth spins through 1 degrees every 4 minutes. So moving on 13 degrees, to “catch up” takes 52 minutes.
  
  • Therefore, 24 hours and 52 minutes elapse between successive times at which the moon is directly overhead at a specific location on the earths surface. This is why the moon rises and sets almost an hour later each night.

Question 25

how far apart is each tide?

Answer 25

• As there are 2 tidal bulges, lunar tides caused by the moon (M2 tides) will occur every 12 hours 26 minutes. The period of the M2 lunar tidal component is 12.43 hours.

Question 26

what are the 2 different tyeps of lunar orbit tides?

Answer 26

• Diurnal or semidiurnal tides: review the lunar orbit.

Question 27

what is the maximum declination of the moon?

Answer 27

• The current obliquity of the earths orbital plane to the ecliptic is 23.5 degrees. So add 5 degrees, the inclination of the lunar orbit (the angle between the lunar orbit and the ecliptic), so that the maximum declination of the moon in the sky will be 28.5 degrees.

Question 28

what is the direction of inclination of the lunar orbit?

Answer 28

• The direction of inclination of the lunar orbit varies over a 18.6 year cycle.
  
  • So the maximum declination of the moon in the sky varies on this 18.6 year cycle.

Question 29

what are diurnal tides?

Answer 29

• Because of the declination of the moon, northern and southern high latitudes commonly face only one high tide and one low tide, called Diurnal tides

Question 30

what is the lunar month?

Answer 30

• Lunar month- new moon to new moon is 29.5 days about every 7 days, the earth alternates between -spring tide, and neap tide.

Question 31

what is the spring tide alignment?

Answer 31

• Spring tide alignment of earth-moon-sun system, lunar and solar bulges constructively interfere. Large tidal range

Question 32

what is the neap tide?

Answer 32

Neap tide: earth-moon-sun system at right angles (quadrature), lunar and solar budges destructively interfere, small tidal range.

Question 33

what are the four major interrelated factors which later the earths tides?

Answer 33

1. The earths landmasses
   
   2. The shallow depth of the oceans in relation to the wavelength of tides
   3. The latitudinal variation of orbital velocity due to the earths spin around its axis
      The Coriolis effect

Question 34

what are dynamic tides?

Answer 34

When these factors are included in calculations of tides, the calculated tides are called dynamic tides.

Question 35

what are the effects of continents and ocean depth?

Answer 35

N-S oriented landmasses prevent the tide waves from travelling around the world.
When the tide waves encounters a continent, its energy is dissipated or reflected, and the wave must be “restarted” on the other side of the continent

Question 36

what is the coriolis effect?

Answer 36

• Water moving in a tide wave is subject to the Coriolis effect
  
  • As the wave travels from E to W, it is deflected to the right in the N. Hem, and to the left in the S. Hem.

Question 37

what is the amphidromic system?

Answer 37

• May lead to unique form of standing wave: “an amphidromic system”. The high and low tide points move around the basin in a rotary path. Counter clockwise in N hem. Clockwise in S.

Question 38

why are tide waves well developed around Antartica and the poles?

Answer 38

• Tide waves is well developed around Antarctica.
  
  • Enters Atlantic around southern tip of Africa
  • Flows towards equator, interacts with weaker Atlantic tide waves, deflected to left, tides higher on west side.
  • Amphidromic system forms in N Atlantic where it is deflected to the right.

Question 39

what are storm surges?

Answer 39

• When extreme spring tides coincide with storms, can get exceptional levels. Additional sea level rise due to low atmospheric pressure. Additional sea level rise due to winds.
  
  • Hurricanes can create exceptional storm surges, up to 6 m.

Question 40

what are tide currents in estuaries and rivers?

Answer 40

• Tides extend far into many bats, estuaries and rivers, where they are affected by: the extremely shallow water depths, freshwater flow and friction with the sea floor.

Question 41

what happens to tides in very shallow water?

Answer 41

• In very shallow water, the crest of the tide waves moves in the significantly deeper water than the trough.

Question 42

how do high tides catch up with low tides in rivers?

Answer 42

• High tide tends to catch up to the low tide in estuaries or rivers where the tide travels long distances through shallow water.

Question 43

how can river tides be modified?

Answer 43

• As a result, river tides can be modified with a long period between high and low tides, but a very short period between low and high.

Question 44

how are tidal bores created?

Answer 44

• Tidal bored are created in estuaries with high tidal ranges when the current in the flooding tide is faster than the speed of a shallow water wave at that depth and the leading edge of the wave must force its way up the bay and estuary.

Question 45

what is the tidal energy?

Answer 45

• The tide moves a huge amount of water twice a day, and harnessing it provides a great deal of energy, 20% of Britain’s needs.
  
  • Although the energy supply is reliable and plentiful, converting it into electrical power is not easy.
  • 8 main sites around Britain where tidal power stations could be usefully built.

Question 46

what is the historic background of tide energy?

Answer 46

Historic background: used by humans since 787 AD>
Exploitation of the potential energy provided by the tidal range. Harness the kinetic energy provided by the tidal currents.
High tidal range and estuaries or bays with narrow openings are all good.

Question 47

what are tidal barrages?

Answer 47

• In narrow bays or estuaries
  
  • High tidal prism
  • Use of sluice gates
  • 2 way turbines

Question 48

what are the problems with tidal barrages?

Answer 48

cost effectiveness, environmental impacts, low capacity factors, high capital cost.

Question 49

what are underwater tidal turbines?

Answer 49

• Mainly in coastal areas
  
  • Predictable tidal currents
  • Current velocities 2-3 m per second.
  • Available turbine farm creation

Question 50

what are the problems with underwater tidal turbines?

Answer 50

small power generation, not well developed

Question 51

what are tidal energy advantages?

Answer 51

Non-polluting energy source, reducing of greenhouse and acid gasses emissions, predictable, renewable

Question 52

what are disadvantages of tidal energy?

Answer 52

reduced tidal flow, silt built up, affect biology of area, economics, low capacity factors, high cost of construction, not well developed technology.