Mrs. Sumrall - Science 2nd 9 Weeks' Review

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Science

• 9 Weeks Review

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9 Weeks Review
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• ALABAMA COURSE OF STUDY OBJECTIVES
• 2 Define mass, volume, and density.
• 6 - Compare effects of gravitational force on
  Earth, on the moon, and within space.
• 
  
• 6A - Identifying contributions of Newton to the
  study of gravity
• 
  
  
• 6B -Describing how a spring scale is used to
  measure weight
• 
  
  

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• In everyday usage, we rarely distinguish between
  weight and mass. If a man says I weigh 150
  pounds he is probably talking about his mass. If
  a woman says I felt weightless when I was
  swimming she is probably talking about her
  weight.
• This does not cause many problems in our
  day-to-day lives, BUT IT IS a major issue for
  scientists.

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• An objects mass is the amount of matter it
  contains. An objects mass does not depend on its
  location. If you move a bowling ball from Earth
  to the Moon, it will still contain the same
  amount of matter. The metric units for mass
  include the kilogram (kg) and the gram (g).

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• Unlike mass, weight is a force. Weight is the
  force of gravity pulling on an object.
• The weight of an object (w) its mass (m)
  multiplied the gravitational acceleration (g) at
  that spot, w mg.
• The unit of weight in the metric system is the
  same as the unit of forcethe newton (N). (Story
  about Sir Isaac Newton at end of PP)

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• An objects weight can be changed either by
  altering its mass or by moving it to a location
  with stronger gravity (like Jupiter) or weaker
  gravity (like the Moon or Mars).

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In 1676, Robert Hooke discovered that the length
a spring stretches equals applied force.
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• Because weight is a type of force, it can be
  measured on a spring scale.
• Examples of spring scales include bathroom scales
  and produce scales.
• If you use a spring scale to weigh a piece of
  fruit on Earth and on the Moon, it will correctly
  show that the fruit has less weight on the Moon
  than on Earth.
• The force of gravity pulling the fruit down is
  much weaker on the Moon.

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• A balance measures mass by comparing the weights
  of two objects.
• An object placed on the pan of a balance exerts a
  downward force equal to its weight.
• An object of equal weight placed on the other pan
  will balance the pans.

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• Because the pans are in the same gravitational
  field, the equal weights of the two objects imply
  their equal masses.
• If two objects have equal mass on Earth, they
  will have equal mass on the Moon, Mars, Jupiter,
  or anywhere else.

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• ALABMA COURSE OF STUDY OBJECTIVE
• 6C -Explaining how air resistance affects
  falling objects

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• The most surprising and misunderstood aspect of
  free fall is that..
• light objects can fall at the same rate as much
  heavier objects.
• In a vacuum, a feather falls as quickly as a
  hammer!

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• But why do objects of different weight fall at
  the same rate?
• Galileo noted that light and heavy objects fell
  at the same rate. Why? An iron cannonball and a
  wooden ball of the same size, when dropped from
  the leaning tower of Pisa, hit the ground
  together. But the force on the cannonball--its
  weight--is larger. Why doesn't it fall any
  faster?

Italian physicist, mathematician, astronomer, and
philosopher
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• Newton gave the correct answer heavier objects
  also have greater inertia.
• Inertia is the tendency of a body to resist
  acceleration the tendency of a body at rest to
  remain at rest or of a body in straight line
  motion to stay in motion in a straight line.

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• Not only is the cannonball pulled down with a
  force that is (say) 10 times larger, it also
  resists acceleration 10 times more strongly.
• Newton expressed it in a mathematical
  formula--"Newton's second law of motion,"
• Simply stated, the result is that both objects
  fall at the same rate (ignoring air resistance).

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• Suppose a rock is 100 times more massive than a
  pebble. It would take 100 times as much force to
  move the rock as it would take to move the
  pebble.
• If the gravitational forces on the two objects
  were equal, the pebble would fall more quickly.
  But the force of gravity is not the same on all
  objects.

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• The force of gravity on an object, also called
  its weight, is proportional to the objects mass.
  
• Therefore, the rock is being pulled by 100 times
  as much force as the pebble, and they will fall
  at the same rate.

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• In air, the motion of falling objects is opposed
  by the frictional force of air resistance.
• Air resistance depends on the surface area of
  the falling object.
• If two objects have the same mass, air resistance
  will slow the object with larger surface area
  more.

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• The faster an object is moving, the greater the
  air resistance.
• This resistance cancels some of the gravitational
  force so the object does not speed up quite as
  much.
• As the object goes faster and faster, air
  resistance cancels more and more of the
  gravitational force, so it speeds up less and
  less.

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• Two objects with the same surface area, such as a
  golf ball and a ping pong ball, experience the
  same force of air resistance.
• But the less massive object (the ping pong ball)
  is slowed down more.
• Massive objects, such as runaway trains, take a
  lot of force to stop!

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• This explains why the golf ball falls more
  quickly than the soccer ball without a parachute
  but more slowly with a parachute.
• Without a parachute, the soccer ball has much
  greater air resistance than the golf ball, so it
  is slowed more than the golf ball.
• With a parachute, the air resistance of each ball
  is about the same. The golf ball, which is
  lighter, is slowed down more.

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http//www.apprenticezone.com/davinci/games/main/g
ames.html
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Current Events Connection Unit Confusion

• A dizzying variety of units have been used to
  describe the mass or weight of objects pounds,
  ounces, tons, stones, grains, drams, carats,
  pennyweights, scruples, talents, shekels,
  newtons, kilogramsthe list goes on and on.
• Until fairly recently, little or no distinction
  was made between units of mass and units of
  weight.

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• To avoid confusion, scientists use System
  Internationale (SI) units.
• This system, also known as the metric system, is
  convenient to use because it is easy to convert
  from one unit to another.
• There are 100 centimeters in a meter, and 1000
  meters in a kilometer. Compare this to 12 inches
  in a foot and 5,280 feet in a mile!

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• The United States is one of the few countries in
  the world that has not adopted the metric system
  for everyday use. Occasionally this leads to
  serious problems. Perhaps the most notorious case
  of unit confusion occurred in 1999. NASA
  scientists were collaborating with engineers from
  Lockheed Martin to control the flight of the Mars
  Climate Orbiter. While the NASA group calculated
  forces in newtons, the engineers assumed that the
  numbers were given in units of pounds-force. The
  resulting miscalculation sent the 25 million
  probe hurtling into the Martian atmosphere at a
  steep angle, where it burned up.

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• ALABAMA COURSE OF STUDY OBJECTIVES
• 2 Define mass, volume, and density.
• 2C  Relating density to the sinking or
  floating of an object in a liquid

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• Density refers to the mass found in a given
  volume of a substance. It is calculated by
  dividing the mass of a substance by its volume D
  m / V.
• A density of 2 g/mL means that a single
  milliliter of a substance has a mass of 2 grams.
•  
• In general, dense objects can be thought of as
  being more tightly packed than objects with low
  densities. Sand in a jar is more tightly packed,
  or dense, than pop tabs in the same size jar.

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• Because density does not depend on the amount of
  substance, it can be used to identify substances.
  Each milliliter of water has a mass of one gram,
  so water has a density of 1.0 g/mL. Gold has a
  density of 19.3 g/mL, and silver has a density of
  10.5 g/mL. (Note A milliliter, 1 mL, is
  equivalent to one cubic centimeter, 1 cm3 or 1
  cc.)

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• Place a can of soda and diet soda of the same
  brand in a tank of water. The diet soda will
  float while the regular soda will sink. What
  could the differences could be.?
• (The regular soda has approximately 10
  tablespoons more sugar, giving it more mass and
  making it denser than diet soda.)

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Historical Connection

• There is a legend about Archimedes, an ancient
  philosopher and mathematician, which takes place
  in the third century B.C.
• The king of Syracuse, Hiero, had given a jeweler
  a brick of pure gold to make into a crown. When
  the crown was completed, the king was suspicious
  that the jeweler had substituted a less precious
  metal for the gold, so he asked Archimedes to
  demonstrate whether the crown was pure gold or
  not.

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• At that time, there were no tools to measure
  irregular shapes, so it became quite a perplexing
  problem for Archimedes. He knew the crown was the
  same mass as the original bar of gold. Archimedes
  determined that if the crown had more volume than
  the original bar, it would be less dense and
  therefore not made of pure gold.

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• The problem was that Archimedes did not know how
  to find the volume of the crown. One day he
  accidentally filled his bathtub to the top. As he
  stepped into the tub, the water overflowed.

He realized that if he collected the water that
had overflowed, he would know the volume of his
body. Archimedes was so excited by his discovery
he jumped out of the tub and ran naked down the
street, all the while yelling, Eureka! I have
found it!
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• Archimedes used a balance to measure a block of
  gold with a mass equal to the crown. He placed
  the block of gold and the crown into a tank of
  water. Sure enough, the crown displaced more
  water than the gold, proving the crown was less
  dense than pure gold (and was therefore a fake!).

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Sir Isaac Newton

• Newton, an Apple,
• and You by Jeanette CainHave you ever
  wondered why things fall down and not fall up? If
  you've heard of Sir Isaac Newton, then someone
  has probably told you that an apple fell on his
  head causing him to think of this very same idea!
  Thank goodness the apple didn't fall on his head,
  but only close enough for him to start thinking
  about things falling down, rathern than not
  falling up. Do you think he was the first person
  to ever see an apple fall to the ground? Probably
  not, but he was the first to decide that he
  wanted to know "Why?"

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• Isaac Newton was born on Christmas Day in 1642.
  His father died only a few weeks before he was
  born and his mother was very poor.
• No one really expected that a genius would be
  born into a family lacking riches or money, but
  Newton proved them wrong. He was a small, sickly
  child and could not play games with the other
  children.

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• Sounds a little like Rudolph the Red-Nosed
  Reindeer, doesn't it? He also enjoyed doing
  things by himself, so he made up games that he
  could play by himself. When he was not making up
  games, he was reading. At the age of ten Newton
  went to a public school, but he had to room with
  a druggist whom he did not know. Although Newton
  was sickly, he enjoyed playing tricks on the
  druggist and was most often in more than just a
  little trouble with the druggist.

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• When he decided to use his time through positive
  actions, he made little windmills that worked and
  kites that flew.
• He would make clocks that could run on water
  power, write poetry, and much to his mother's
  amazement he would draw charcoal sketches on the
  wall of his bedroom! Obviously, Newton's mom
  didn't have Mr. Clean!

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• His mother sent for his return home when he was
  14, because she needed him to run the farm.
  Newton enjoyed learning so much that he could be
  found behind the bushes studying from his books.
  It was his uncle who realized that Newton would
  never make a farmer and made the suggestion that
  Newton be sent to college.

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• He attended Trinity College in Cambridge and
  became well-known for his mathematic skills. It
  is said that he knew more than his professors!

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• In 1665, England faced a great plague which
  caused the college to close. At 23 years old,
  Newton had to return home to his mother's farm
  once more. Now this is where the story of Newton
  and the apple had its beginnings. He thought
  about gravity and sometimes in the morning hours
  he would sit on the edge of his bed (only
  half-dressed) and think about gravity until
  dinner time.

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• He had bought prisms at a county fair for a few
  pennies. He experimented with these penny prisms
  and showed that a beam of sunlight is composed of
  the six colors of the rainbow.

Those colors are red, orange, yellow, green,
blue, and violet. He even ground lenses and
mirrors to make a new type of microscope. Newton
also invented a new type of mathematics called
calculus. Each time he finished one of these
experiment, he returned to his ideas about
gravity.
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• Newton said that the moon is caught between two
  forces (1) gravity, which pulls it toward the
  earth and (2) centrifugal force, caused by its
  rotating, which pulls it outward. Since the moon
  is held by these two forces it cannot fly toward
  the earth and it cannot fly away from the earth.
  So, the moon does the next best thing-it moves in
  a curved path around the earth!

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• You can try your own experiment with these two
  forces at work by tying a string on a ball and
  whirl it in the air around you.
• Ask an adult for help. You can feel it pulling
  away, but your grip on the string is like the
  force of gravity. It will hold the ball so that
  it moves in a circle around you.
• You, like Newton have found and proved that the
  Earth's gravity has a tendency to pull all
  objects toward its center.

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• Newton then reasoned that if gravity explained
  the curved path of the moon, then couldn't it
  also explain the curved path of all the planets
  and heavenly bodies in the solar system? Newton
  said that just as the earth holds the moon, the
  sun would hold the earth and all the other
  planets.

Even the comets would be held with the sun's
gravitational pull. This is called the Universal
Law of Gravitation. The sun's force of gravity
will hold all the planets in their orbits.
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• This law also explains why a space ship can orbit
  the earth. It is the whirling motion that forces
  the space ship away from the earth, but it is
  gravity that pulls the space ship back toward the
  earth.
• These two forces balance one another and will
  allow a spacecraft to travel in an orbit. Not
  everyone understood this at first, but at that
  time these were new ideas and very strange and
  different from what people had believed.

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• From a sickly and poor start in life, Isaac
  Newton made many discoveries. His book Principia
  was published in 1687. Some people say that this
  was one of the greatest single achievements of
  the human mind.

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• He was president of the Royal Society for 24
  years and was knighted by Queen Anne.

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• When Newton died on March 20, 1727, at the age of
  85, he was buried in Westminster Abbey.

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• Sir Isaac Newton

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Selected Web Resources

• Your weight on other worlds http//www.explorator
  ium.edu/ronh/weight/
• Weight on other planets http//www.teachervision.
  fen.com/planets/lesson-plan/353.html
• Make a balance http//www.raft.net/ideas/Measurin
  g20Mass.pdf
• Measuring matter http//www.dmturner.org/Teacher/
  Library/4thText/MatPart2.html
• Types of force http//www.physicsclassroom.com/Cl
  ass/newtlaws/U2L2b.html
• Weight and mass http//ourworld.compuserve.com/ho
  mepages/Gene_Nygaard/weight.htm
• Metric units in the US http//www.unc.edu/rowlet
  t/units/usmetric.html
• Mars probe http//www.space.com/missionlaunches/l
  aunches/orbiter_errorupd_093099.htm
• The story of Archimedes http//www.cde.state.co.u
  s/cdeadult/IGLA/pdf/ScienceSink.pdf
• Activities to explore density http//www.teachers
  .net/lessons/posts/116.html
• Related activities http//pzweb.harvard.edu/ucp/c
  urriculum/density/index.htm