2.4 Acceleration of Bodies Due to Gravity Free Fall Objects fall at a uniform rate due to gravity. This is called free fall or acceleration due to gravity. In free fall situations air resistance is ignored. The warm up activity on page 64 demonstrated this when the paper is placed on top of the book. Air resistance is effectively removed during the fall for the piece of paper. Symbol for Acceleration Due to Gravity The symbol g is given for acceleration due to gravity Value of g on Earth The value of g on Earth and used for our purposes is 9.81 m/s2 Text Page 64

2.4 Acceleration of Bodies Due to Gravity Projectiles Projectile Motion Projective motion refers to any object moving through the atmosphere under the influence of gravity. In Physics 11 only projectile motion in the vertical, or up and down, direction will be considered. A Note about that Pesky Negative Sign Some books and websites state g is -9.81 m/s2. Other times g is 9.81 m/s2. Both are correct given the situation. If the objects motion is both up and down, direction has to be considered because acceleration is a vector measurement. Usually up is positive and down is negative. So in this situation g is -9.81 m/s2. When the object is going up or down only, then we can call that direction positive and g is 9.81 m/s2. You could use g as -9.81 m/s2 and you would get the same answer. It’s just easier to use a positive number. Text Pages 66 - 67

2.4 Acceleration of Bodies Due to Gravity Projectiles - 2 Text Pages 66 - 67 You should be able to visualize and describe the motion of a ball leaving your hand, going up in the air and coming back down into your hand. Why is the acceleration of the ball 9.81 m/s2 at the highest point of the ball’s trip (Point B)?

2.4 Acceleration of Bodies Due to Gravity Key Questions In this section, you should understand how to solve the following key questions. Page 66 – Practice Problems 2.4.1: #2 Page 67 – Quick Check: #1 Page 68 – 2.4 Review Questions: #2