1.6 Acceleration Near Earth’s Surface 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. 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 simultaneously.

1.6 Acceleration Near Earth’s Surface

1.6 Acceleration Near Earth’s Surface If you accidentally drop your mother’s favourite dish, you will directly (and I suppose indirectly) feel how significant the effect of gravity is. Acceleration due to Gravity ( 𝒈 ) occurs when an object falls freely. It does not depend on the mass of the object. Physicists have determined the average measure of 𝒈 near the surface of the Earth to be 9.8 m/s2 [down]. The value of 9.8 m/s2 assumes that there are no forces other than gravity acting on an object; such as air resistance.

1.6 Acceleration Near Earth’s Surface The value of 𝒈 varies at different locations on the Earth. Its value is based on the object’s distance from the centre of the Earth (radius). The further an object is from the Earth’s centre (higher altitude), the lower the value of 𝒈 . Many of the high-jump, long-jump, and pole vaulting records at the 1968 Olympic Games in Mexico City were broken; attributed in part to the lower value of 𝒈 . The value of 𝒈 is different on other planets and celestial bodies.

1.6 Terminal Velocity In real life scenarios, there will always be air resistance. Air resistance causes objects to accelerate 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. When an object reaches terminal velocity, it will fall at a constant velocity. SP #1,2 p.41 SP #1,2 p.42

1.6 Homework Practice # 1 p.41 Practice # 2 p.42 Questions #3-7 p.43