4.2b Notes Writing the YELLOW
Objectives Explain why objects that are thrown follow a curved path. Compare circular motion with motion in a straight line.
Projectile Motion Thrown objects don’t travel in straight lines, they curve downward because of gravity http://img.sparknotes.com/content/testprep/bookimgs/sat2/physics/0012/projectile.gif
Horizontal & Vertical Motion When you throw a ball, your hand exerts a force pushing ball forward Horizontal motion Gravity accelerations ball downward Vertical motion Gravity exerts unbalanced force on ball Changes direction to forward & downward Ball appears to travel in a curve
Horizontal and Vertical Distance Throwing and dropping a ball from the same height Both travel in same vertical distance Thrown ball travels more horizontal distance Click image to view movie
Centripetal Force Object entering a curve Object going around a curve Speed doesn’t change Acceleration does because direction changes Object going around a curve Change of direction of velocity is toward center of curve
Centripetal Acceleration Acceleration toward the center of a curved or circular path
Centripetal Force The net force exerted toward the center of a curved path According to the second law of motion, when an object has centripetal acceleration, the direction of the net force on the object must be toward the center of the curved path
Centripetal Force & Traction Car traveling around a curve, centripetal force must be acting on the car to keep it moving in a curved path This centripetal force is the frictional force, or the traction, between the tires and the road surface
Centripetal Force & Traction Anything that moves in a circle is doing so because a centripetal force is accelerating it toward the center
Gravity = Centripetal Force When whirling an object tied to a string above your head, the string exerts a centripetal force on the object that keeps it moving in a circular path. In the same way, Earth’s gravity exerts a centripetal force on the Moon that keeps it moving in a nearly circular orbit.
In-Class Assignment 4.2 Reinforcement WKT