8th Grade Science

Ocean Tides

2

At Low Tide there can be lots of Beach

33

At High Tide not so much

4

Ogunquit Beach, Maine

4

5

Low Tide

High Tide

Bay of FundyNew Brunswick, Canada

Butler Middle School

Merrimack River & Atlantic Ocean

Butler Mid SchoolLowell, MA

Lawrence

Haverhill

NewburyportNashua

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

10

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

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 drivepropellers connected to generators

12

Quiz #2: What question

might a Scientist ask now?

What Causes High and Low Tides?

To explain Tides we need to understand Gravity

Sir Issac Newton1642-1727

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 MD

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

HighTide

HighTide

LowTide

LowTide

High Tides occur on opposite sides of Earth

Point AMoon pulls on water at Earth’s surfaceWater flows toward A

Point BMoon pulls on entire EarthLeaving the water behind

Points C & DLow tides occur between the two high tides

Spring and Neap Tides

NewMoon

Spring Tide, higher than normal tide

FullMoon

Neap Tide, less difference between low & high tides

1st quarter

3rd quarter

90º

Vocabulary• Range

– 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

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