gravity

1. GRAVITY
• Near the surface of the Earth, all objects will accelerate down
at the same rate if there are no other forces acting on them
besides gravity
• The acceleration due to gravity is:
or g = 9.8 m/s2
]
down
[
m/s
8
.
9 2

g

( This applies even when the object is moving up)
a
v
v
a
It also applies
when an object
stops for an instant
at the peak of its
flight.
a
at the same rate
• The acceleration is the same regardless of the mass of the
object
regardless of the
mass of the object

2. • The value of “g” is slightly different in different locations
 g decreases as you go higher in altitude
(e.g. Mt Everest: 9.79 m/s2)
 g is less near the equator and increases as you move
towards either pole (North pole: 9.83 m/s2)
• The acceleration due to gravity is different on other planets
or moons
 on moon gmoon = 1.6 m/s2
 on Jupiter gJupiter = 24.8 m/s2
• The maximum acceleration humans can handle without
serious damage is about 30g (30 x g)
• Astronauts experience about 3g at liftoff

3. Terminal Velocity
• air resistance tries to slow down objects as they move
through the air
• air resistance increases as things go faster
• when an object is dropped, it accelerates down, but air
resistance causes the acceleration to decrease as the
object speeds up
v=0
a=9.8 v
a<9.8
v
a<<9.8
v
a = 0
• eventually the air resistance is so big that it balances
the influence of gravity and
• the velocity stays constant after that  the
the acceleration is zero
terminal velocity

4. Acceleration at beginning = slope = 9.8 m/s2
• For a person, the terminal velocity is about 200 km/h
• the terminal velocity depends on the amount of surface area
that is pushing through the air, as well as the shape of the
object, its density, and the density of the air
Terminal speed = 50 m/s