# 6 - AP1 Forces.pdf - Newtonu2019s Laws Isaac Newton u2022...

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Newton’s Laws
Isaac Newton Came up with 3 Laws of Motion explains work by Galileo and Kepler published in Mathematical Principles of Natural Philosophy in 1687 Discovered that white light was composed of many colors all mixed together. Invented new math calculus binomial expansion theorem
What is Force? A force is a push or pull on an object. Forces cause an object to accelerate To speed up To slow down To change direction
Newton’s First Law (Law of Inertia) A body in motion stays in motion at constant velocity A body at rest stays at rest unless acted upon by a net external force.
Implications of Newton’s 1 st Law If there is zero net force on a body ٫ no acceleration ٫ constant velocity it can not turn, it can not speed up, it can not slow down.
What is Zero Net Force? Even though there are forces on the book, they are balanced. Therefore, there is no net force on the book. Σ F = 0 Physics A book rests on a table. Gravity pulls down on the book. F G The table pushes up on the book. F Table
Zero Net Force Forces on the piano: F floor F g F push F friction Vertical forces balance → no net force ∑F y =0 Horizontal forces balance → no net force! ∑F x =0
“Normal” force The “normal force” is the name of the force of a surface pushing back on an object. The normal force is always perpendicular a surface. A person standing on the floor has a normal force of the floor pushing upward. A person leaning against the wall has a normal force of the wall pushing back. A cup of coffee sitting on a table has a normal force of the table pushing back (upward) on it. There is NO normal force on a balloon floating in the air!
Diagrams Draw a force diagram (a free body diagram ) for a book sitting on a table. N F g Physics N F g
Mass and Inertia Chemists: mass is the amount of “stuff” or “matter” a substance has. Physicists: mass is the same thing as inertia , which is the ability of a body to resist acceleration by a net force. m = symbol for mass unit: kg (kilogram)
Mass and Weight Many people think mass and weight are the same thing. They are not. Mass is inertia , or resistance to acceleration. Weight (W) can be defined as the force due to gravitation attraction (F g ) . W = F g = mg
Weight Weight = force due to gravity = F g F g = mg can be used when “g” is known g = 9.8 m/s 2 (on the surface of the earth) measured in N (Newtons)
Weight problem