SECTION 3.3 FREE FALL Define acceleration due to gravity. Objectives Define acceleration due to gravity. Solve problems involving objects in free fall.
INTRO Do Heavier objects fall faster than lighter ones? Free Fall – the motion of a body when air resistance is negligible and the motion can be considered due to the force of gravity alone.
ACCELERATION DUE TO GRAVITY Galileo concluded that, neglecting the effect of air, all objects in free fall had the same acceleration. Galileo was the first to show that all objects fall to Earth with a constant Acceleration. As long as Air Resistance can be ignored the acceleration due to gravity is the same for all objects at the same location on Earth. Acceleration Due To Gravity – has a special symbol which is “g”. It is the acceleration of an object in free fall that results from the influence of Earth’s Gravity. Since acceleration is a Vector Quantity “g” must have both magnitude and direction.
ACCELERATION DUE TO GRAVITY We will use up as the positive direction. We will use down as the negative direction. (use for Lab 3) So a Falling Object (Lab 3) has a Negative Velocity. Thus the Acceleration is Negative On the surface of Earth a freely falling object has an acceleration “g” of –9.8 m/s2. Use this for the Accepted value when finding your percent error in Lab 3. Assuming no air resistance all problems involving motion of falling objects can be solved by using the equations developed in this chapter with the acceleration “a” replaced by “g”.
ACCELERATION DUE TO GRAVITY vf = vi + gt vf2 = vi2 + 2gd d = vit + ½ gt2
BALL THROWN UPWARD The ball reaches its max height at the instant of time when its velocity is ZERO. At the top of the flight the Velocity is Zero but Acceleration is still –9.8 m/s2 (gravity). Note: when you throw something up it takes half the time to reach the max height and the other half to fall back to where it started.
FREE FALL RIDES Do Practice Problems p. 74 # 42-46 As motion problems increase in complexity, it becomes increasingly important to keep all the signs consistent. This means that any displacement, velocity, or acceleration that is in the same direction as the one chosen to be positive will be positive. Thus any displacement, velocity, or acceleration that is in the opposite direction as the one chosen to be positive will be Negative. It is important to be consistent with the coordinate system to avoid getting the signs mixed up. Do 3.3 Section Review p. 75 # 47-52