Newton’s First Law of Motion - Inertia Chapter 2 Newton’s First Law of Motion - Inertia

Stationary Earth Earth is heavy It looks like the sky is moving Easier to imagine the sky can move It looks like the sky is moving We have no sensation of our motion Rotating Earth would make objects fly off of the surface Stellar Parallax

Stellar Parallax Hipparchus 150 BC June Sun January

Aristotelian Universe Terrestrial Realm Composition predicts motion natural tendencies Fire and Air tend to rise Earth and Water tend to sink Overall tendency to seek rest Objects are corruptible (changing)

Aristotle attempted to understand motion by classification. 1. ARISTOTLE ON MOTION Aristotle attempted to understand motion by classification. Two Classes: Natural and Violent

Aristotelian Universe Celestial Realm Celestial Objects composed of Aether Self luminous but does not consume Motion is constant, circular Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere

The falling speed of an object was supposed to be proportional to its weight. Galileo’s Experiment

Developed a mathematical model for a Sun-centered solar system Nicholas Copernicus 1473 - 1543 (Niklas Koppernigk) Developed a mathematical model for a Sun-centered solar system

Galileo Galilei 1564-1642 Among the first to turn a telescope to the sky Developed the Scientific Method Believed in the popularization of science Developed the Law of Inertia

He tested with planes. Demo - Ball and incline plane The change in speed depended on the slope of the incline. Seemed that the ball was trying to achieve the same vertical height.

Isaac Newton 1642 - 1727

Newton’s Laws The 1st Law A body continues to move as it has been moving unless acted upon by an external force.

Newton’s First Law No mention of chemical composition. No mention of terrestrial or celestial realms Force required when object changes motion. Acceleration is the observable consequence of force acting.

Net Force Force is a vector We must add all the forces acting on the body 5 N 10 N 5 N 5 N 5 N 0 N 5 N 10 N 5 N

Equilibrium When the net force is zero (SF = 0) Acceleration is zero Velocity may not be zero

Static Equilibrium Velocity is zero Examples: Scales pushing up Normal up Weight down Computer setting on a table Weighing yourself on a set of scales Hanging from a tree Tree pulling up Weight down Car parked on an incline Normal Friction Weight down Weight down

Mass and Inertia Inertia is a property of a body that resists changes in motion Mass is a measure of the amount of matter in a body Inertia and Mass are the same concept Units – Kg or slugs

Weight Force of gravity pulling on the mass of the body Units – Newtons or Pounds A newton is about the weight of a small apple One kg weighs 2.2 lbs. W = mg g = acceleration due to gravity at the surface of the Earth = 32 ft/s2 = 9.8 m/s2

Inertia Demonstrations Demo - Table setting Demo - Bottle, hoop, and chalk