1. Free Fall
Motion Notes Day 4

2. Galileo Galilei
Galileo formulated the laws that govern the motion of objects in free fall 2

3. Free Fall
All objects moving under the influence of gravity only are said to be in free fall
Free fall does not depend on the object’s original motion
All objects falling near the earth’s surface fall with a constant acceleration
The acceleration is called the acceleration due to gravity, and indicated by g 3

4. Acceleration due to Gravity
Symbolized by g
g = -9.8 m/s2
g is always directed downward
toward the center of the earth
Ignoring air resistance and assuming g doesn’t vary with altitude over short vertical distances, free fall is constantly accelerated motion 4

5. Free Fall – an object dropped
Initial velocity is zero
Let up be positive
Use the kinematic equations
Acceleration is g = -9.8 m/s2
vi= 0
a = g 5

6. Free Fall – an object thrown downward
Vi= (-)
a = g
a = g = -9.8 m/s2
Initial velocity ≠ 0
With upward being positive, initial velocity will be negative 6

7. Free Fall – an object thrown upward
a = g = -9.8 m/s2
Initial velocity ≠ 0
With upward being positive, initial velocity will be positive
final velocity = 0
Vi= (+)
a = g 7

8. Free Fall - Example
If a rock is dropped from a building, and it takes 18 seconds to reach the ground, how tall is the building? 8

9. Practice A baseball is thrown up vertically with a velocity of 12 m/s.
a. What is the maximum height the baseball reaches?
b. How long does it take to reach max height?
c. What is the velocity when it hits the ground?

10. Practice A baseball is thrown up vertically with a velocity of 12 m/s.
a. What is the maximum height the baseball reaches?
Practice

11. Practice A baseball is thrown up vertically with a velocity of 12 m/s.
a. d= 7.3 m (We can use this now!!)
b. How long does it take to reach max height?
Practice

12. Practice A baseball is thrown up vertically with a velocity of 12 m/s.
a. d= -7.3 m (negative because falling!!)
b. t= 1.22s (We can use this now!!)
c. What is the velocity when it hits the ground? (Now we assume falling with Vi = 0)
Practice

13. Homework Complete 1-16 on 1D Kinematics Worksheet
Answers will be posted on Website!!!
Tomorrow and Friday we will review graphing
Quiz Friday
Motion Test Thursday, Sept 12!!!

14. Position-time graphs show how the position of an object changes over time.
So, the slope of a d/t graph tells us the VELOCITY of the object.

15. Velocity-time graphs show how the velocity of an object changes over time.
So, the slope of a d/t graph tells us the ACCELERATION of the object.

16. The slope is constantly changing, so that means the velocity is changing. Changing velocity is called ACCELERRATION.

17. The area under the graph represents displacement (Δd).17