Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine [e-mail]

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Introduction to Physical ScienceMonday,
Wednesday, ThursdayTom Burbinetomburbine_at_astr
o.umass.edu
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Density

• Density Mass/Volume
• Mass is usually in grams or kilograms
• Volume is usually in cm³ or m³

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Densities

• Density of water 1 g/cm³ 1,000 kg/m³
• Density of iron 8 g/cm³ 8,000 kg/m³

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Weight density

• Weight density weight/volume

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Pressure

• Pressure Force/Area
• Unit of pressure is a Pascal,
• which is a newton per square meter

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Pressure in a liquid

• When you swim, you feel the pressure of the water
  plus air above you
• It is the weight of the fluids (water and air)
  above you
• Swim deeper, more pressure

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Pressure in a Liquid

• Liquid pressure weight density x depth

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Pressure in a liquid

• Liquid pressure is exerted equally in all
  directions

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Buoyant Force

• Upward acting force, caused by fluid pressure,
  that opposes an object's weight

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Equal Volumes

• Equal volumes feel equal buoyant forces
• Cork would float, aluminum would sink, and lead
  would sink faster
• Difference in their behavior is due to their
  weight

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Archimedes (287 BC-212 BC)

• Greatest scientist of antiquity
• Needed to determine if silver had been
  substituted for gold in a crown for a king
• Mass could easily be determined but not mass
• Discovered that you could determine the volume of
  the crown by submerging it in water
• Density (mass/volume) could be determined and
  compared to pure gold
• This story may not be true

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Archimedes Principle

• An immersed body is buoyed up by a force equal to
  the weight of the fluid it displaces

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Meaning

• When an object is immersed in water, it feels
  lighter
• Apparent weight of object is the weight of object
  minus the buoyant force

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Principle of Flotation

• A floating object displaces a weight of fluid
  equal to its own weight

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Why does an iron ship float?

• Iron is about eight times as dense as water
• When submerged, displaces 1/8 of a ton of water
• If the iron is in a bowl and displaces 1 ton of
  water, it floats

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• Buoyant force equals the weight of the fluid it
  displaces
• Denser fluids exert more buoyant force upon a
  body than less-dense fluids of the same volume
• A ship floats higher in salt water than in fresh
  water because salt water is slightly denser than
  fresh water so it has higher mass and exerts a
  higher buoyant force

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• http//www.youtube.com/watch?veQsmq3Hu9HA

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Any Questions?