Some Particular Forces Weight = mg (direction: downward) mass 9.8 m/s2 Free body diagram: mg Mass and weight are not the same thing! Mass is an intrinsic property of an object Weight depends on the value of gravity

The Support()Force Fs= support force S F = 0, since at rest mg Any object in contact with a surface experiences a support force (Fs) perpendicular to that surface In the picture above: Fs = mg But this is not always the case!…….

Solve Unknowns Determine the magnitude of the forces acting on the 2 kg masses at rest below. ∑Fx = 0 and ∑Fy = 0 mg = 20 N FN = 20 N Solve Unknowns ∑Fy = 0 FN - mg = 0 FN = mg = 20 N

Examine the following diagrams and write 2-3 facts and figures about them… Understand this page and you have…

Tension (T) – force applied by a string or rope Ex: 5 N T = 5 N We say “the tension in the string is 5 N” The tension is the same throughout a string, even when it passes over pulleys: T

Ex: A person pulls a crate across the ice with a rope Find the horizontal acceleration of the crate. 15 N m=35 kg 30

Static friction (fs) – keeps objects from moving Friction (f) – a force that opposes motion between two surfaces in contact motion (or attempted motion) friction Two types of friction: Static friction (fs) – keeps objects from moving Kinetic friction (fk) – opposes motion while moving Both depend on: Surfaces in contact Amount of normal force (FN)

Heat energy is always produced. Friction is a force. It occurs when two surfaces rub together. Heat energy is always produced.

Friction always opposes motion. Drag Thrust

Streamlining objects can reduce this effect.