Chapter 7 Rotational Motion & Law of Gravity Section 7-3 Causes of Circular Motion

Force that Maintains Circular Motion Is:  The net force on an object directed toward the center of the object’s circular path.  Necessary for circular motion.  Measured in SI units of Newtons (N)  F c

Figure 7-10 : When a ball is whirled in a circle, a force directed toward the center of the ball’s circular path acts on it.

Formulas for F c  F c = mv t 2 / r Force that maintains circular motion = mass x (tangential speed) 2 / distance to axisForce that maintains circular motion = mass x (tangential speed) 2 / distance to axis  F c = mrω 2 Force that maintains circular motion = mass x distance to axis x (angular speed) 2Force that maintains circular motion = mass x distance to axis x (angular speed) 2

Practice Problem  Pg. 261 Sample 7H

Newton’s Universal Law of Gravitation  Gravitational force is a field force that always exists between two masses, regardless of the medium that separates them.  Gravitational force (F g ) depends on the distance between two masses.  The force between two masses decreases as the masses move farther apart.

Formula for F g  F g = G m 1 m 2 / r 2  Gravitational Force = Constant x mass 1 x mass 2 / (distance between center of masses) 2  G is a universal constant = x Units = N ∙ m 2 / kg 2Units = N ∙ m 2 / kg 2

Practice Problem  Pg. 264 Sample 7I

Assignment  Practice 7H pg. 261 #1-4  Practice 7I pg. 265 # 1-3