Ocean Tides
Butler Middle School
8th Grade Science
Bob, Paul, Ms. Adams, Dec 4, 2012
At Low Tide there can be lots of Beach
2
At High Tide not so much
3
Ogunquit Beach, Maine
4
Low Tide
High Tide
5
Bay of Fundy
New Brunswick, Canada
Butler Middle School
Merrimack River & Atlantic Ocean
Haverhill
Nashua
Newburyport
Lawrence
Butler Mid School
Lowell, MA
High and Low Tides
• 2 high tides and 2 low tides
within every 24 hour day
• High & Low tides don’t occur at
the same time every day
• Similarly, New & Full moons
don’t occur on the same day
each month
• The Changing tides can be
used to produce energy
Quiz #1: What best describes
all the previous slides?
(a) an experiment
(b) a procedure
(c) data and observations
(d) scientific method
(e) an advertisement for Ogunquit, Me
10
Tidal Energy
• Tides move huge amounts of water each
day
• Getting control of it can produce a lot of
energy
Largest Tidal Power Station is in France
Similar to wind power, tides can drive
propellers connected to generators
Quiz #2:
What question
might a Scientist
ask now?
12
What Causes High and Low
Tides?
To explain Tides we need to understand Gravity
Sir Issac Newton
1642-1727
English Scientist
Newton’s Universal Law of Gravitation
•All objects attract or pull on each other with an
invisible force without contact
•The pull of gravity between 2 objects
depends on their masses and distance
distance between them
•The bigger the objects the greater the
attraction
•Gravity gets weaker as distance gets bigger
m
D
M
Math form of Newton’s Gravity Law
What Causes High and Low Tides?
• Answer is Complicated:
– The Moon’s Gravity is mostly responsible
– The Sun’s Gravity plays a smaller role
because the sun is so far away compared to
the Earth-Moon distance
– There are other reasons which you will
learn about if you become a physicist or an
astronomer
Gravity of Moon & Sun pull on Earth’s
Oceans
Gravity keeps the moon in orbit
around the earth
Gravity keeps the earth in orbit
around the sun
A Closer look at High & Low Tides
Low
Tide
High High Tides occur on opposite sides of Earth
Tide
Point A
Moon pulls on water at Earth’s surface
Water flows toward A
Point B
Moon pulls on entire Earth
Leaving the water behind
Points C & D
Low tides occur between the two high tides
High
Tide
Low
Tide
Spring and Neap Tides
Spring Tide, higher than normal tide
New
Moon
Full
Moon
Neap Tide, less difference between low & high tides
1st quarter
90º
3rd quarter
• Range
Vocabulary
– Difference between high and low tide
• Neap Tide
– Occurs when Range is smallest
– Sun, Earth, Moon form 90º angle
• Spring Tide
– Occurs when Range is largest
– Sun, Earth, Moon are aligned
• Ebb Tide
– Water is moving away from shore
• Flood Tide
– Water is moving toward shore
• Slack Tide
– About 1 minute between water moving in then out
– or the interval between Flood & Ebb tides
Tides link to Gravity
• Ocean Tides on Earth are caused mainly by the pull of
the Moon’s Gravity
– Sun’s Gravity has a smaller effect
• Newton’s Universal Law of Gravitation
– Force of Gravity is invisible
– All objects attract or pull on each other
– The force of gravity between 2 objects depends on their
masses and distance between them
– The bigger the objects the greater the attraction
– Gravity gets weaker as distance gets bigger