# CIRCULAR MOTION PES 1000 PHYSICS IN EVERYDAY LIFE CIRCULAR MOTION PES 1000 PHYSICS IN EVERYDAY LIFE UNIFORM CIRCULAR MOTION For an object moving on a circle at constant speed The speed is constant, but the direction is not Acceleration is a change in velocity, but speed is constant The change in velocity is only in its direction Therefore, the acceleration is toward the center (centripetal) Centripetal Force is a label for whatever force is causing the path to curve If the centripetal force is removed, the ball travels in a straight line tangent to the circle at the point of release Fcent acent

EXAMPLES Ball on a string Centripetal force is from the string Moon in orbit Centripetal force is from gravity Car on a flat, circular road Centripetal force is from friction of tires on the road Airplane on a circular path Centripetal force is from part of the lift when the plane banks into the turn BANKING PLANE OR BANKED ROAD Flift

The airplane must bank inward toward the center of its turn The force of lift tilts inward The inward part of the lift is centripetal It is the cause of the inward acceleration Flift (inward) acent acent FG The road is banked inward toward the center of the curving road

Part of the normal force is inward Part of the friction is also inward The sum of these parts is centripetal They are the cause of the inward acceleration FG acent acent Ff Finward FN

CENTRIPETAL VS. CENTRIFUGAL FORCE Centripetal force: Acts on the ball Acts inward Centrifugal force: Acts on the string holder Acts outward (fugal means to flee) It is the equal and opposite reaction (Newtons Third Law) to the centripetal force

It is felt because of the inertia of the ball which opposed the inward acceleration Fcentripetal Fcentrifugal WHAT DOES CENTRIPETAL FORCE DEPEND m=mass ON? The centripetal force depends on: v=speed The mass of the turning object more mass requires more force The speed of the turning object A faster object requires more force The radius of the curved path The smaller the circle, the more force is required

Fcentripetal The formula to find the force is this: Fcent = m*v2/r r=radius GENERAL CURVILINEAR MOTION So far, we have examined motion in 1-D along a line, and motion with uniform speed in a circle atangent If the motion is more complicated, we just look at a moment in time as the object moves along a curvilinear path with varying speed. At this instant: You can draw a circle that just touches the curve. Uniform circular motion describes the circular

motion around this circle at the speed at this instant. Part of the total acceleration is centripetal. Motion in 1-D describes the motion along the path. The rest of the total acceleration is along the path (tangent) You can do this at any point along the path acent v=speed radius radius atangent acent v=speed SIMULATIONS The 2-D Motion and Ladybug Revolution simulations let you experiment with circular motion The can be found here:

https://phet.colorado.edu/en/simulation/legacy/motion-2d https://phet.colorado.edu/en/simulation/legacy/rotation Lets play with the simulations: (You may need to install Java script in your browser: https://java.com/en/download/ ) CONCLUSIONS Uniform Circular Motion describes motion on a circle at constant speed Since velocity is changing direction, there must be force and therefore acceleration toward the center Centripetal force is the central force on the turning object and centrifugal force is the reaction force on the object causing the turning Many types of forces can be centripetal Combining motion in 1-D and uniform circular motion can describe more general types of motion