4.2b Notes

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 the ball forward Horizontal motion Gravity accelerates the ball downward Vertical motion Gravity exerts unbalanced force on the ball Changes direction of ball from simply forward to forward & down Ball appears to travel in a curve

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 Acceleration Acceleration toward the center of a curved or circular path

Centripetal Force Object entering a curve Object going around a curve Speed doesn’t change Acceleration does change because direction changes Object going around a curve Change of direction/velocity is toward center of curve

Centripetal Force The net force exerted toward the center of a curved path According to the second law of motion, The direction of the net force is in the same direction as the centripetal acceleration toward the center of the curved path

Centripetal Force & Traction If a car is 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