Forces Or Trust in the Force LukeAni Forces

Forces Or Trust in the Force Luke/Ani

Forces in General • A Force is a push or pull, an interaction between two bodies • Force is a vector quantity • Adds vectorally (tip to tail) • Can be decomposed into perpendicular components that are independent of one another • Force is measured in Newtons (Kg m/s 2) • 1 Newton ~ ¼ pound

Force Types • Contact forces are forces that require physical contact between the two objects in the interaction. • E. g. Springs, muscular pushes and pulls, friction, normal force, air resistance, ropes, chains • Non-Contact or action at a distance forces do NOT require physical contact between two objects in interaction • E. g. Gravity, Electric and Magnetic Forces, Strong and Weak Nuclear Forces • Forces on object are those things touching it and gravity

Force Definition Direction Magnitude Equation Weight Gravitational force of planet on object Towards center of planet Fweight = mg where g is the gravitational field strength (-9. 8 N/kg near Earth) Spring Force of spring on object In direction opposite spring’s displacement Fspring = -kx where k measures spring stiffness Normal Force Perpendicular force of contact between two surfaces Perpendicular to surfaces contact Never larger than net force in opposite direction Frictional Force Horizontal force of Parallel to surface contact in direction that opposes motion Ffriction =m. Fnormal where mu depends on stickiness of two surfaces Air Resistance Opposite direction of body’s motion Fair resistance = Cv 2 where C depends on shape and mass of object Common Forces contact between two surfaces Force between air molecules and body moving through air

Check Question • What is the weight of 2 kg? a) b) c) d) 2 N 1 N 20 N 0. 2 N

Net Force • Sum of all forces in a linear direction (eg horizontal and vertical). • If net force is NOT zero then object will accelerate in that direction • If net force is equal to zero then object will move with a constant velocity in that direction (eg stay stationary or retain initial velocity)

Examples of Net Force • Stationary box on floor • Mover leaning on stationary box on floor • Mover pushing box on floor at constant velocity • Mover pushing box on floor at constant acceleration • Object falling w/ air resistance

Ropes, Chains, Strings and Equilibrium Problems • Ropes, strings, and chains exert a contact force on other objects called a tension. • Equilibrium Tension Problem has an object suspended by strings, chains and ropes. • Since no acceleration occurs, net force = 0. • Forces in horizontal direction balance • Forces in vertical direction balance • As rope becomes more horizontal the tension in the rope must increase