WEIGHTLESSNESS AND ORBITAL MOTION
© Simon Porter 2007

CONCLUSION QUESTIONS 1-5

CONCLUSION QUESTIONS 6-10

WEIGHTLESSNESS
Weightlessness – free from the effects
of gravity (Zero g)
A sensation experienced by an individual
when there are no contact forces acting on
that individual.
An example is
when in a state
of free-fall.
Gravity and Inertia CREATE sensation of
Weightlessness

ELEVATOR FUN!

WEIGHTLESSNESS
So there is a force of gravity on the astronaut, but no reaction
force from the floor so the astronaut feels weightless.
© Simon Porter 2007
YouTube
- flying
dog
YouTube
- Greg
Olsen -
Drinking
water on
the ISS
YouTube -
Zero G
Puke Bag

DRINKING WATER – ISS (GREG OLSEN)

ORBITAL MOTION
 A result of the combination of an objects forward inertia and the
downward pull of gravity.

ORBITING SATELLITES
•Since Earth is
CURVED, objects
with enough
inertia will stay in a
state of freefall,
orbiting
Earth, creating the
sensation of
weightlessness.

KEEPING THE WORLD SAFE FROM
MR. HASTINGS DOG!
From a table, medium kick.

HOW FAR CAN YOU KICK A DOG?
Gravity

HARDER KICK?

HARDER KICK
Gravity

SMALL CANNON?
Woof!
(help)

SMALL CANNON
Gravity
Woof!
(help)

BIGGER CANNON?

BIGGER CANNON
Gravity
Gravity

EVEN BIGGER CANNON?

EVEN BIGGER CANNON
Gravity
Gravity
Gravity

VERY BIG CANNON?

VERY BIG CANNON
Gravity

HUMUNGOUS CANNON?

DOG IN ORBIT!
The dog is
now in orbit!
(assuming no
air resistance
of course)

DOG IN ORBIT!
The dog is
falling towards
the earth, but
never gets
there!

DOGS IN ORBIT!
The force that
keeps an
object moving
in a circle is
called the
centripetal
force (here
provided by
gravity)
Gravity

Inertia and gravity combine to keep Earth
in orbit around the sun and the moon in
orbit around the Earth.
A combination of gravity and inertia keeps
the moon in orbit around the Earth.
WHY DO EARTH AND THE MOON
REMAIN IN THEIR ORBITS?
If there were no gravity, inertia would cause
the moon to travel in a straight line. If only
gravity existed, the earth would be pulled into
the sun.

DESCRIBE WHY AN ASTRONAUT WOULD
FEEL WEIGHTLESS.

DRAW A DIAGRAM OF EARTH ORBITING
THE SUN (LABEL FORCE ARROWS)