1. 4.2b Notes

2. Objectives Explain why objects that are thrown follow a curved path.
Compare circular motion with motion in a straight line.

3. Projectile Motion
Thrown objects don’t travel in straight lines, they curve downward because of gravity

4. 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

5. 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

6. Centripetal Acceleration
Acceleration toward the center of a curved or circular path

7. 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

8. 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

9. 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

10. Centripetal Force & Traction
Anything that moves in a circle is doing so because a centripetal force is accelerating it toward the center

11. 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.

12. In-Class Assignment
4.2 Reinforcement WKT