Transcript Lesson 11 Orbital motion

Do now!
• Mr Porter is giving you the “contents”
sheet for this topic. He will be collecting
your folders in next Friday 13th (!) and he
expects them all to be complete and in the
correct order – or else!
Satellites
How far could you kick a 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
Woof!
(help)
Gravity
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!
Gravity
The force that
keeps an
object moving
in a circle is
called the
centripetal
force (here
provided by
gravity)
Other examples
Earth’s
gravitational
attraction on moon
Uniform Circular Motion
• This describes an object going around a
circle at constant speed
Direction of centripetal
acceleration/force
Change in velocity
VB
VA
VB
VA
VA + change in velocity = VB
The change in velocity (and thus the
acceleration) is directed towards the centre of
the circle.
Uniform circular motion
The centripetal acceleration/force is always directed
towards the centre of the circle
Centripetal force/acceleration
velocity
Not uniform velocity
• It is important to remember that though the
speed is constant, the direction is
changing all the time, so the velocity is
changing.
Uniform speed ≠ uniform velocity
How big is the centripetal
acceleration?
a=
2
v
r
where a is the centripetal acceleration (m.s-2), r is
the radius of the circle (m), and v is the constant
speed (m.s-1).
How big is the centripetal force?
F=
2
mv
r
from F = ma (Newton’s 2nd law)
Centripetal Force - The Real Force
Note!
• There is no such thing as centrifugal force!
(at least not until you get to university!)
CENTRIFUGAL
Types of orbits
Geostationary
The satellite orbits once every 24 hours, so appears to
stay above the same point on the earth’s surface
Looking from
above the North
pole
Geostationary
Useful for communications satellites. Also for weather
over one area.
Polar
Satellite orbits over the poles
Polar
Useful for mapping and remote sensing when the whole
of the earth’s surface needs to be studied
Some famous satellites
Sputnik
th
(4
October 1957)
Sputnik
•
•
•
•
•
•
th
(4
October 1957)
Russian
84 kg, 58cm diameter
800km above the earth
30 000km/h
Orbited every 90 mins
Fell after 92 days
Sputnik 2 (a month later)
Sputnik 2 (a month later)
• 450 kg
• Carried a dog! (Laika)
• Laika is believed to have died from
overheating in the cabin a few hours after
launch
It’s a dogs life.
Hubble Space telescope
Hubble Space telescope
• Launched in 1990
• 13.1m long
• Doesn’t have to see through the earth’s
atmosphere
That’s it!
Can you try some questions now?
Read pages 119
to 126.
Choose four
questions to
answer, one very
easy, one easy,
one medium and
one hard.