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Download Linking Asteroids and Meteorites through Reflectance
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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?
