Orbits
Objectives: (i) analyse circular orbits in an inverse square law
field by relating the gravitational force to the centripetal
acceleration it causes;
(j) define and use the period of an object describing a circle;
(k) derive the equation T2 = 4 π2 x r3
GM
from first
principles;
(l) select and apply the equation T2 = 4 π2 x r3
GM
for
planets and satellites (natural and artificial);
(m) select and apply Kepler’s third law T 2 = k r 3 to solve
problems;
(n) define geostationary orbit of a satellite and state the uses
of such satellites.
Outcomes
ALL MUST
Be able to define the period of an object describing a circle.
Be able to look at data like period, radius, gravitational field strength, to
relate gravitational force to acceleration.
Be able to define a geostationary orbit of a satellite and state the uses of
such satellites.
MOST SHOULD
Be able to select and apply Kepler’s third law T 2 = k r 3 to solve problems
in different situations.
Be able to select and apply the equation T2 = 4 π2 x r3
GM
correctly for planets and satellites (natural and artificial);
SOME COULD
Be able to derive the equation T2 = 4 π2 x r3
GM
from first principles;
1.Gravity
17th Century England…
A man sits in an orchard
and ponders the universe…
Why do things
always fall
downwards and
never upwards?
Why do the
planets orbit
around the sun?
Why does the
moon orbit
around the
earth?
Of course there
must be an
invisible force
that acts between
all things!
The force is
GRAVITY
Gravity is an attractive, non-contact force that
acts between all objects.
The bigger the object the greater the force of
gravity.
The further the objects are from each other the
less the force of gravity.
The further the objects are from each other the
less the force of gravity.
2. Orbits
Cannon Simulator
• http://jersey.uoregon.edu/vlab/Cannon/