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### Free Fall

Motion Notes Day 4

Galileo Galilei

1564 - 1642

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

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

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

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

Free Fall – an object thrown downward

a = g = -9.8 m/s2

Initial velocity ≠ 0

With upward being positive, initial velocity will be negative

Vi= (-)

a = g

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

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?

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?

Practice

A baseball is thrown up vertically with a velocity of 12 m/s.

a. What is the maximum height the baseball reaches?

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

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)

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!!!

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.

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.

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

The area under the graph represents displacement ( is changing. Changing velocity is called ACCELERRATION.Δd).

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