Kinematics – The study of motion

Questions From Reading Activity?

Objectives  Understand that, within certain limits, the acceleration due to gravity on the surface of the Earth is constant and acts toward the Earth’s center.  Know that the value of the acceleration due to gravity on the surface of the Earth is 9.81 m/s 2

Objectives  Understand how Equations 2-10a to 2-10c can be modified for motion due to gravity as follows:  These equations assume that the acceleration due to gravity is constant and air resistance is negligible.

Objectives  Understand the importance of consistency in choosing a frame of reference and choosing which directions are positive and negative during problem solving.  Solve problems involving free-falling objects.

Video: Force of Gravity

Let’s Experiment

 What did we learn?  Things fall at the same rate = gravitational acceleration is constant  The acceleration is approximately equal to 9.81 m/s 2

Galileo  At a given location on the Earth and in the absence of air resistance, all objects fall with the same constant acceleration.  This is the acceleration due to gravity, g.  g ≈ 9.80 m/s 2 or 32 ft/s 2  The acceleration due to gravity is always toward the center of the earth.

Gravity Varies LocationElevationg New York San Francisco Denver Pike’s Peak Equator North Pole09.832

Gravity Varies  Why does gravity vary?

Gravity Varies  Why does gravity vary?

So What Does This All Mean?

 All of the equations we developed for horizontal motion can be used for vertical motion  Substitute g = 9.80 m/s 2 for a  Change x to y to represent vertical displacement  You now have to decide which direction is positive (up or down) and which is negative  Make sure that your value for g (positive or negative) matches the direction

So What Does This All Mean? Horizontal EquationsVertical Equations

Let’s Try Some Problems

Summary Review  Do you understand that, within certain limits, the acceleration due to gravity on the surface of the Earth is constant and acts toward the Earth’s center?  Do you know that the value of the acceleration due to gravity on the surface of the Earth is 9.81 m/s 2 ?

Summary Review  Do you understand how Equations 2-10a to 2-10c can be modified for motion due to gravity as follows:  These equations assume that the acceleration due to gravity is constant and air resistance is negligible.

Summary Review  Do you understand the importance of consistency in choosing a frame of reference and choosing which directions are positive and negative during problem solving?  Can you solve problems involving free- falling objects?

#32-45 Homework