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Circular motion the movement of an object at constant speed around a circle with fixed radius. axis- straight line around which rotation takes place. rotation- object turns around an internal axis. Ex. ice skater revolution- object turns around an external axis. Ex. earth around the sun. Rotational speed Linear speed- distance/time Tangential speed- speed along a circular path. Rotational speed- number of rotation per unit of time. Ex. carousel horses travel at same rotational speed but different tangential speed. Tangential speed- radial distance times the rotational speed. V=rw Centripetal force force that causes an object to follow a circular path. Ex. force holding occupants safely in a rotating carnival ride. Fnet=mv2 r centripetal acceleration always points toward the center of the cicular motion. period(T)=time needed for an object to make one complete revolution. distance traveled= circumference centripetal acceleration equals the velocity squared divided by the radius revolution= distance/circumference

=Universal Gravitation and Mass= - As the mass of either object or both objeect increases, the force of gravitational attraction increases. - Newton's law of universal gravitations applies to all objects. - As the distance of the 2 objects increases, the force of attractions is expotentially smaller.

//__SAMPLE PROBLEM __// Determine the force of gravitational attraction between the Earth (m=5.98 x 10 24 kg) and a 70-kg physics student if the student is standing at sea level, a distance of 6.37 x 10 ﻿6 m from Earth's center.

__SOLUTION: __ F ﻿grav =Gm ﻿1 m ﻿2 /d ﻿2

F= (6.67 x 10 -11 ) (5.98 x 10﻿ 24 ) (70) / (6.37 x 10 6 ) 2 F= 2.79 x 10 16 / 4.06 x 10 13 F= 688N

Grounding
- Touching a body to Earth to eliminate excess charge.