Chapter 6 Circular Motion and Other Applications of

Chapter 6 Circular Motion and Other Applications of Newton’s Laws

Uniform Circular Motion n A force, Fr , is directed toward the center of the circle This force is associated with an acceleration, ac Applying Newton’s Second Law along the radial direction gives

Uniform Circular Motion, cont n n n A force causing a centripetal acceleration acts toward the center of the circle It causes a change in the direction of the velocity vector If the force vanishes, the object would move in a straight-line path tangent to the circle

Centripetal Force n The force causing the centripetal acceleration is sometimes called the centripetal force n n This is not a new force, it is a new role for a force It is a force acting in the role of a force that causes a circular motion

Forces that causes centripetal acceleration We are familiar with different types of forces such as Gravity, friction, normal forces and tension etc. Should we add centripetal forces in this list? Answer: No, It is not new kind of force. A common mistake in the free body diagram is to draw all usual forces and then to add another vector for the centripetal force. But it is not a separate force---it is simply one or more familiar forces that causes circular motion

Examples Motion of the earth around the sun: Gravitational force An Object sitting on rotating turn table: Friction force The rock whirled horizontally on the end of string: string Tension in the For an amusement-park Patron pressed against the inner wall of rapidly rotating room: normal force exerted by the wall

Conical Pendulum n n The object is in equilibrium in the vertical direction and undergoes uniform circular motion in the horizontal direction v is independent of m

The conical Pendulum

Motion in a Horizontal Circle n n The speed at which the object moves depends on the mass of the object and the tension in the cord The centripetal force is supplied by the tension

How fast can it spin The force cause to the centripetal acceleration is the tension in the string

Horizontal (Flat) Curve n n n The force of static friction supplies the centripetal force The maximum speed at which the car can negotiate the curve is Note, this does not depend on the mass of the car

What is the maximum speed of the car? The static friction force enable the car to move round the circular path

Banked Curve n n These are designed with friction equaling zero There is a component of the normal force that supplies the centripetal force

The Bank Exit Ramp

Loop-the-Loop n n This is an example of a vertical circle At the bottom of the loop (b), the upward force experienced by the object is greater than its weight

Loop-the-Loop, Part 2 n At the top of the circle (c), the force exerted on the object is less than its weight