Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine

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 ( 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 ( ) Leaning Tower of Pisa experiment Dropped things of different weights Except for air resistance, things fall at the same rate

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

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 ns/flight/rocketactivitynetforce.gifhttp:// 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/s 2

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/s 2

Homework

Any Questions?