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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What keeps the planets orbiting around the Sun?
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What keeps the planets orbiting around the Sun?

• Inertia - Resistance of any physical object to a
  change in its state of motion or rest
• Gravity Attractive Force
• The inertia of each planet is offset by the sun's
  gravity
• The result is stable orbits around the sun

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Aristotle (384-322 BC)

• Divided motion into two classes
• Natural motion dealt with the nature of bodies
  (smoke rises, heavy things fall)
• Violent motion something was pushed or pulled

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• Heavy things fall faster than light things
• Moving objects had forces on them to keep them
  moving

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Galileos (1564-1642) Leaning Tower of Pisa
experiment

• Dropped things of different weights
• Except for air resistance, things fall at the
  same rate
• http//www.youtube.com/watch?vgtdiHDxh3LU

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Inertia

• Inertia property by which objects resist
  changes in motion

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Exercise
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Mass

• Mass quantity of matter in an object (measure
  of inertia)
• Use kilograms or grams

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Horizontal and vertical

• Horizontal is sideways
• Vertical is up and down

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Force

• Push or pull
• Force is given in units of Newtons

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Equilibrium

• Mechanical equilibrium Net force on an object
  is zero

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Weight

• Weight Force due to gravity on an object
• Your weight on the Moon will be 1/6 your weight
  on Earth
• http//www.youtube.com/watch?v16D0hmLt-S0

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Friction

• Friction - resistive force that opposes motion or
  attempted motion of an object past another with
  which it is in contact
• Always acts in opposite direction of motion

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Support Force

• Weight of the book acts downwards
• Support (or normal) force acts upwards
• Sum of the forces is equal

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Net Force

• Net Force is the combination of all the forces on
  a body
• http//www.dynamicscience.com.au/tester/solutions/
  flight/rocketactivitynetforce.gif

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Net Force

• If the net force on an object is zero, the object
  has a constant speed

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Exercise
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Friction

• Static Friction - the friction between 2 things
  that aren't moving
• Dynamic friction - the friction between 2 moving
  objects

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Speed

• Speed distance/time

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Velocity

• Velocity is a description of how fast something
  is going and in what direction

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Acceleration

• Acceleration change in velocity/time interval
• For example,
• Acceleration (10 m/s)/(5 s)
• Acceleration 2 m/s2

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Net Force

• If the net force on an object is increasing, the
  object is increasing in speed (accelerating)
• If the net force on an object is decreasing, the
  object is decreasing in speed (decelerating)

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Earths Gravity

• As something falls, it increases speed
• The acceleration of gravity on Earth is 9.8 m/s2

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Homework
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Any Questions?