Chapter 2 Newtons First Law of Motion Inertia

Chapter 2 Newton’s First Law of Motion - Inertia

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

Stellar Parallax u Hipparchus 150 BC June Sun January

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

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 u Motion is constant, circular u Objects are incorruptible (not changing) Meteors and comets were phenomena of the Earth’s atmosphere u

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

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

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

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

Isaac Newton 1642 - 1727

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

u No mention of chemical composition. u No mention of terrestrial or celestial realms u Force required when object changes motion. u Acceleration is the observable consequence of force acting.

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

Equilibrium u When the net force is zero (SF = 0) Ø Acceleration is zero Ø 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 Car parked on an incline pulling up Friction Weight down Normal Weight down

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

Weight u Force of gravity pulling on the mass of the body q Units u. A newton is about the weight of a small apple q One u. W – Newtons or Pounds kg weighs 2. 2 lbs. = mg qg = acceleration due to gravity at the surface of the Earth • = 32 ft/s 2 = 9. 8 m/s 2

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