Unit 5: Magnetism

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Unit 5 Magnetism
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History of a magnet

• People in Magnesia found the rock magnetite
• This rock attracts materials that contain iron

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Magnetism

• The attraction of a magnet for another object
• One part of a magnetic rock will always point in
  the same direction
• Towards a certain north star, lodestar
• Magnetic rocks also became known as lodestones

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Magnetic poles

• All magnets have 2 ends, each called a magnetic
  pole
• A pole is the area of a magnet where the magnetic
  effect is the strongest.
• One pole of a magnet will always point toward the
  north and is labeled the north pole
• The other end is labeled the south pole, the
  north and south are opposites

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Checkpoint

• What do you know about north and south poles of a
  magnet?

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Interactions between Poles

• 2 north poles repel
• 2 south poles repel
• 1 north and 1 south attract
• Magnetic poles that are alike repel each other
  and magnetic poles that are unlike attract each
  other.
• The force of attraction or repulsion between
  magnetic poles is magnetism.

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Consider This

• What would happen if you broke a magnet in half?

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Magnetic Fields

• Magnetic force is strongest at the poles of a
  magnet
• Magnetic field is the region of magnetic force
  around a magnet
• Magnetic field lines spread out from one pole,
  curve around a magnet, and return to the other
  pole

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Why is it a magnet?

• Magnetic properties depend on the atomic
  structure of a material
• A moving electron produces a magnetic field
• The spinning and orbiting motion of an electron
  make each atom a magnet

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Earth as a Magnet

• Compass a device that has a magnetized needle
  that can spin freely
• The needle typically points north
• There is a immense (large) magnetic field
  surrounding earth, just like a bar magnet
• Most likely because of the circulation of molten
  iron and nickel within the Earths core.

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• WWW

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What on Earth?

• Earths geographic poles are not identical to its
  magnetic poles

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Gravity (pg 156-157)

• The force that pulls objects toward each other
• An attraction between the centers of mass of 2
  objects
• Keeps the moon orbiting around earth,
• and earth around the sun.
• Distance affects the pull of gravity
• On earth, it is the force that pulls
• objects straight toward the center
• of the earth.

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Weight

• The force of gravity on a person or object at the
  surface of a planet.
• Note this is different from mass mass does not
  take gravity into consideration, it is only the
  amount of matter in an object.
• Different on each of the planets or moons
• The larger the object, the greater the pull of
  gravity on it and the greater the weight of the
  smaller object
• The further an object is from a gravitational
  field, the less it will weigh

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Free fall

• When the only force acting on an object is
  gravity.
• During free fall, the object will accelerate
  toward the center of the earth at 9.8
  meters/second squared.
• All objects accelerate at this rate, regardless
  of their mass.

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Air Resistance

• Friction caused when an object falls through air.
• This is why 2 things with the same mass may not
  fall at the same rate to the ground

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Ponder this

• Which will hit the ground first, a piece of paper
  or a crumpled up piece of paper?

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Universal Gravitation

• States that the force of gravity acts between all
  objects in the universe.
• Means you are not only attracted to Earth, but to
  all objects
• Gravitational pull depends on mass
• So why are you not pulled toward the desk, or
  your book?

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Newtons 3 Laws of Motion

• 1.An object at rest will remain at rest and an
  object in motion will remain in motion unless
  acted upon by an unbalanced force.
• Ex throwing a ball
• 2. The net force on an object is equal to the
  product of its acceleration and its mass.
• F M x A
• Ex pulling a wagon
• 3. For every action there is an equal and
  opposite reaction.
• Ex balloon deflating

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Layers of earth

• Crust
• Lithosphere
• Mantle
• Core

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Crust

• Layer of rock that forms Earths outer skin
• Includes soil, water, mountains, and rocks
• Ranges from 5-40 km thick
• Thinnest under ocean (oceaninc crust)
• Thickest under mountains (continental crust)

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Mantle

• Layer of hot rock
• The uppermost part of the mantle and the bottom
  of the crust form the lithosphere
• Temperature and pressure increase with depth
• Soft layer in the mantle is the asthenosphere
• Material in it can flow slowly
• Nearly 3000km thick

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Outer Core

• Liquid
• Layer of molten metal that surrounds the inner
  core

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Inner Core

• Dense ball of solid metal
• Such great pressure does not allow metals to
  spread out and become liquid

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Earths core

• Both cores together are just a little smaller
  than the moon
• Pgs. 354-355 in book

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Convection Currents

• Heat transfer is the movement of heat energy from
  a warmer object to a cooler object.
• Cold is the absence of heat
• 3 types of heat transfer
• Radiation
• Conduction
• Convection

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Radiation

• Transfer of heat energy through empty space
• Does not involve contact of materials
• E.x. sunlight, bonfire

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Conduction

• Heat transfer by direct contact
• E.x. you touching a hot spoon in a pot of hot
  water

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Convection

• Heat transfer involving the movement of fluids
  including liquids and gases
• Caused by differences in temperature density
• A convection current is the flow that transfers
  heat within a fluid
• The heating and cooling of the fluid, changes in
  the fluids density, and the force of gravity
  combine to set convection currents in motion

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Convection in Earths Mantle

• Convection currents flow in the athenosphere
  (upper mantle)
• As hot mantle comes toward the lithosphere, it
  expands and pushes cooler material towards the
  core