Download Unit 1 - Motion in a Straight Line

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