back to index ofchapters1. Why might it be important to know tide times and conditions if youare going snorkelling?
Ans. The tidal current is not constant. At high water and low water thereis little current. Most of the water moves in 3-4 hours after high tide.These currents may cause safety problems for the snorkeller.
2. Who was the first scientist to correctly explain the reason for tides?
Ans. Sir Isaac Newton was the first scientist to explain the reason fortides.
3. Which has the greatest influence on the tides along our coast: theMoon or the Sun? Explain why.
Ans. Gravitation force depends on the object mass and distance. The sunis a lot larger than the moon but is so far away that its pull is much less.
Gravitation force ???
Therefore the moon has the greatest influence.
4. How long does it take the Moon to orbit the Earth?
Ans. The moon takes 29.5 days to orbit the earth.
5. Why are the tides approximately 50 minutes later each day?
Ans. It takes 24 hours 50 minutes for the moon to be over a particularposition on earth twice.
6. What is centripetal force?
Ans. Centripetal force is the inwardly directed force acting on a bodywhich makes it move in a circle.
7. Why might large tankers always try to enter harbour at high tide?
Ans. The large tankers are easier to manoeuvre when there is little tidalcurrent.
8. Draw the position of the Earth, Moon and Sun when we experience:
a. a neap tide
b. a spring tide
Ans. Neap tide
9. List the four factors that affect the time and height of a tide.
Ans. The factors that effect tide heights and times are
a. The shape of the coastline
b. The depth of the water along the coastline
c. The flow of waters from rivers
d. The weather
e. The slope of the foreshore
10. Define these terms:
a. inter-tidal zone
b. inter-tidal range
Ans. a. The inter-tidal zone is the land exposed when the tides riseand fall.
b. The tidal range is the difference in height between high and low tidesat a given place.
11. The shape of an estuary affects the tidal range.
a. What shape produces large tidal ranges?
b. Where are the tidal ranges greatest?
Ans. If the estuary is funnel shaped a larger tidal range is expectedas the water level will rise more quickly. The Bay of Fundy in Canada.
12. What are king tides?
Ans.
13. Explain why we can have different tidal heights during a single day.
Ans.
14. Currents that move up rivers depend on two factors. What are they?How can the speed be calculated?
Ans. Currents that move up rivers depend on the width of the river andthe depth of the river.
14. a. ebb currents
b. flood currents
c. slack water
d. tidal currents
e. tidal bore
15. Define these terms:
a. apogee
b. perigee
Ans. Perigee - when the moon is at its nearest point to earth on itselliptical orbit.
Apogee - when the moon is at its furthest point from earth.
16. If the tidal range at Mackay is 4 m and high tide is at 8 a.m., predictthe height of the tide at 10 a.m.
17. An amateur fisherman is fishing in a depth of 8 m at 9 a.m. He checksthe tide book to find high tide of 2 m will be at 10 a.m. What will be thedepth of water at 1 p.m? Will the tidal current be greater? Explain youranswer.
1. Collect information on tide times from your local paper for one week.Check your paper for the times of moon rise and sunrise for this same period.How much later does the Moon rise each day?
2. Find the Rance River on a map of France. Where in Australia or NewZealand could such a dam be built? What features would be needed?
3. Use local tide information to find out when the next spring tideswill occur.
4. Obtain a chart of the local area and find the direction of the floodtidal current at various places. It is shown by an arrow with feathers.The direction of the ebb tide is shown by an arrow with no feathers.
5. You could try to build a simple tide measuring gauge like the oneshown in Figure .1 from polypipe. As the tide rises, the yellow ball willindicate the rise in tide.
Suggestion.
Look at photo and build with your Industrial Arts department.
Here are the answers to the questions on Page 140.
1. periodic
2. gravitational
3. phases
4. Sun
5. smaller
6. neap
7. tidal range
8. world
9. coastline
10. shape
11. depth
12. flow
13. slope
14. current
15. tidal
16. estuary
17. Seismic
18. earthquakes