Holt Physics Chapter 4 Section 4 Pages 141-148 Everyday Forces Holt Physics Chapter 4 Section 4 Pages 141-148

Everyday Forces Weight – the magnitude of the force of gravity acting on an object

Fg = mg * Mass ≠ Weight Everyday Forces Fg = force due to gravity (in Newtons) m = mass of object (in kilograms) g = acceleration due to gravity (-9.81 m/s2) * Mass ≠ Weight

Everyday Forces Normal Force – (Fn) – a contact force exerted by one object on another in a direction perpendicular to the surface of contact. On a horizontal surface, Fn = mg

Everyday Forces Normal force diagrams-

Everyday Forces Frictional Forces – Contact forces which oppose applied forces These are the surfaces in contact at a microscopic level.

Everyday Forces 1. Static friction - (Fs) - force exerted on a motionless object by the environment to resist an external force attempting to cause a change in motion

Everyday Forces 2. Kinetic friction – (Fk) – force exerted on a moving object that opposes motion

Everyday Forces * Fk < Fs due to surface adhesion between two surfaces in contact Coefficient of friction (μ) – a ratio of frictional force to normal force between two objects

Coefficient of Friction The coefficient of friction is a ratio of force of friction to the normal force acting between two objects. This completely depends on the objects in contact. Different experimental values have been calculated based on the materials in contact (page 144: table 4-2)

Coefficient of Friction Equations Coefficient of static friction μs = Fs,max Fn Coefficient of kinetic friction μk = Fk

Everyday Forces 3. Air resistance is a form of friction  as velocity increases so does air resistance