Lesson 1.6 ~ Acceleration Near Earth’s Surface

• Acceleration due to Gravity (→g) occurs when an object is in free fall.
• Physicists have determined the average measure of →g near the surface of the Earth to be; →g = 9.8 m/s² [down]
• Before the 1500s, philosopher Aristotle theorized

  that falling objects travelled at constant speeds,

  and more massive objects fall faster than less

  massive objects.
• Galileo Galilei proposed that objects of different

  mass will accelerate at the same rate when

  falling under the influence of gravity.
• What actually affects the rate of fall is the air

  resistance acting on an object due to its mass and

  surface area.
• Galileo supposedly proved this by dropping a cannon ball and a musket ball of different masses off the leaning tower of Pisa. Both hit the ground at the same time!
• The value of g = 9.8 m/s² assumes that there are no forces other than gravity acting on an object; such as air resistance. Assume air resistance is negligible.
• In real life scenarios involving acceleration due to gravity near the surface of the Earth, there will always be air resistance.
• Air resistance causes objects to accerlate at values less than →g.
• An object undergoes terminal velocity when the force due to air resistance acting on the object is equal to the force of gravity. At this point, the object will fall at a constant velocity and will no longer accelerate.
• Free fall: an object that is moving only due to gravity without any resistance (air)