FREE BODY DIAGRAMS AND PROBLEM SOLVING PHYSICS Free
FREE BODY DIAGRAMS AND PROBLEM SOLVING PHYSICS
Free Body Diagrams A pictorial representation of forces acting on an object complete with labels. Consider the box being pulled to the right by a rope across the floor Before we start drawing a FBD, how FBD many forces are acting on the box? a. 1 FA , FT , or T b. 2 Ff , c. Fs , 3 or Fd. K 4 e. 5 F W, Fg N or mg • Weight(W, Fg , or mg) – Always drawn straight down • Normal Force (FN) – A surface force always drawn perpendicular to a surface. • Applied Force (FA , FT , or T) – push or pull as a result of physical contact. Tension: force in ropes and always drawn AWAY from object. • Friction(Ff , Fk , or Fs)Always drawn opposing the motion.
TWO types of Friction n n Static – Friction that keeps an object at rest and prevents it from moving Kinetic – Friction that acts during motion
3 Common Forms of Friction 1. Sliding Friction 2. Rolling Friction 3. Fluid Friction
Sliding Friction occurs when one surface slides across another. Depends on Two Things: 1. Type of Surfaces 2. How hard surfaces are pressed together. F s = µ s FN Fk = µ k. FN
Rolling Friction occurs when one surface rolls across another. Fluid Friction occurs when an object moves through a fluid. Depends on Three Things: 1. Density of the Fluid 2. Surface Area of the Object 3. Speed of the Object
Example #1 a) b) How much does a 0. 25 kg apple weigh? What is the mass of a 15 N toy car?
Example #2 A horizontal net force of 25 N acts on a 12 kg object. What is the acceleration of the object?
Example #3 A 10 -kg box is being pulled across the table to the right at a constant speed with a force of 50 N. a) b) Calculate the Force of Friction Calculate the Normal Force
Example #4 Suppose a 5 kg box is being pulled by a 50 N force at an angle of 30 o above the horizontal. The box accelerates horizontally at 1 m/s 2. a) b) Calculate the Force of Friction Calculate the Normal Force
Example #5 A crane applies a force of 500 N to a 25 kg crate as it is raised into the air. What is the acceleration of the crate?
Example #6 A 1500 N crate is being pushed across a level floor at a constant speed by a force F of 600 N at an angle of 20° below the horizontal. FBD What is the coefficient of kinetic friction between the crate and the floor?
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