Transcript Linking Asteroids and Meteorites through Reflectance

Introduction to Physical Science
Monday, Wednesday, Thursday
Tom Burbine
[email protected]
What keeps the planets orbiting
around the Sun?
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
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
• Heavy things fall faster than light things
• Moving objects had forces on them to keep them
moving
Galileo’s (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?v=gtdiHDxh3LU
Inertia
• Inertia – property by which objects resist changes
in motion
Exercise
Mass
• Mass – quantity of matter in an object (measure of inertia)
• Use kilograms or grams
Horizontal and vertical
• Horizontal is sideways
• Vertical is up and down
Force
• Push or pull
• Force is given in units of Newtons
Equilibrium
• Mechanical equilibrium – Net force on an object
is zero
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?v=16D0hmLt-S0
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
Support Force
• Weight of the book acts downwards
• Support (or normal) force acts upwards
• Sum of the forces is equal
Net Force
• Net Force is the combination of all the forces on a
body
• http://www.dynamicscience.com.au/tester/solutio
ns/flight/rocketactivitynetforce.gif
Net Force
• If the net force on an object is zero, the object has
a constant speed
Exercise
Friction
• Static Friction - the friction between 2 things that
aren't moving
• Dynamic friction - the friction between 2 moving
objects
Speed
• Speed = distance/time
Velocity
• Velocity is a description of how fast something is
going and in what direction
Acceleration
• Acceleration = change in velocity/time interval
• For example,
• Acceleration = (10 m/s)/(5 s)
• Acceleration = 2 m/s2
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)
Earth’s Gravity
• As something falls, it increases speed
• The acceleration of gravity on Earth is 9.8 m/s2
Homework
Any Questions?