4.2 Gravity, Normal Force, and Friction | Intro to Free Body Diagrams | General Physics

Chad provides an introduction to three forces that are often encountered in General Physics 1: gravity and weight, the normal force and friction, both static friction and kinetic friction. These forces also provide the material for introducing net force and free body diagrams, a key tool in how to solve physics problems, and several free body diagram examples are incorporated into the lesson with how to draw free body diagrams explained. The universal force of gravity formula is introduced and explained as well as the much simpler formula for the weight of an object near the surface of the earth where the acceleration due to gravity is a fairly constant 9.8m/s^2. Gravity practice problems involving both equations are solved.

Chad then introduces two contact forces, the normal force and friction. Both are defined and described including both static friction and kinetic friction. It is shown that the normal force is the perpendicular component of a contact force, and that the force of friction is proportional to the normal force as well as the coefficient of friction which is dependent upon the nature of the two surfaces interacting.

Chad introduces the classic physics normal force elevator problems which provide a great one dimensional introduction to how to draw free body diagrams and then apply Newton's first and second laws where the sum of the forces in a direction equal zero for an object not moving or moving with constant velocity or where the sum of the forces in a direction equal mass times acceleration for an object experiencing uniform acceleration. Chad finishes the lesson with problems involving drawing free body diagrams in two dimensions including kinetic friction problems and setting up equations using Newton's first and second laws in two dimensions independently.

00:00 Lesson Introduction
00:40 Gravity and Weight
06:22 Gravity Practice Problems
12:31 Normal Force
15:17 Static Friction and Kinetic Friction
19:50 Normal Force Elevator Practice Problems - How to Draw Free Body Diagrams and Net Force
32:51 Friction Practice Problems - Free Body Diagrams in Two Dimensions

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