Notes over Circular Motion

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Notes over Circular Motion. What is circular motion? The motion of things that are traveling in a circle. Notice that this is similar to projectile motion but instead of ...
Notes over Circular Motion What is circular motion? The motion of things that are traveling in a circle. Notice that this is similar to projectile motion but instead of a semi-circle, we are now working with full circles. When objects travel in a circle there is always an axis that they travel about (around). Axis: A straight line around which circular motion takes place There are 2 types of circular motion Rotation and Revolution. •

Rotation: When an object turns about an “internal” axis (an axis located within the body of the object), also called spin Examples: Figure skater doing spins, a football spiraling, the earth on it’s axis, the platform of a carousel



Revolution: when an object turns around an “external” axis (an axis not necessarily connected to the body) Examples: the earth around the sun, the horses on the carousel,

Clearly, when objects are moving, they have a speed. There are two ways that we can measure the speed of an object in circular motion. •

Rotational Speed (Angular Speed): number of rotations per unit of time It is expressed in revolutions per minute RPM



Tangential Speed: is directly proportional to rotational speed and the distance from the axis (kinda like “regular” speed)

What causes something to move or accelerate? A force The force that causes circular motion is called a centripetal force. Centripetal Force: any force that causes a body to move in a circular path or in part of a circular path, such as rounding a corner •

The only force exerted on an object moving in a circular path is directed toward the center of circular motion

There is another term you may have heard called Centrifugal Force. •

Centrifugal Force: name given to a outward-acting force, and it is useful only in a rotating system



It is different from a real force in that there is no interaction (pair of forces), there is no mass out there pulling on it



There is no reaction counterpart to the centrifugal force that is felt, therefore it is not a real force



Fc (Centripetal Force)



ac (centripetal acceleration)



What do you think these mean?



Basically that the object is moving with circular motion but still accelerating and still has a force keeping it moving.



New formulas for your Formula Sheet Quantity Unit Formula Centripetal Force N Fc = mac 2 Centripetal Acceleration m/s ac= v2/r r is the radius of the circle



Example: A 0.25 kg mass is attached to a 1.00 m length of string. The mass is moving in a horizontal circle at a speed of 15.0 m/s. What is the centripetal force acting on the mass? How much acceleration does the object have?