When two objects interact,
they exert an equal and
opposite force on each
other. (Turn the names
around to check you have
the right forces!)
The downwards force on a
boy due to gravitational
attraction from Earth is equal
and opposite to the upwards
force on Earth due to the
gravitational attraction from
the
If no external forces act,
the total momentum
before a collision is the
same as the total
momentum after a
collision (conservation).
Particles in a
gas move
randomly.
Pressure in gases is
caused by particles
colliding with each
other and the walls
of the container.
Smaller volume or
higher temperature
increase the
pressure as the
particles hit the
container more
frequently.
Pressure = force/area
A rocket pushes hot
gas downwards, so the
gas pushes the rocket
upwards.
E
The highest frequency
radio waves are
microwaves. They are
next to each other in the
EM spectrum
High frequency waves
are used to send
signals to
Geostationary
satellites as they can
penetrate the Earth’s
atmosphere. Low
frequency can be used
for low orbit satellites.
Microwave signals are
sent from a transmitter,
then received and
amplified by the
satellite. Then the signal
is retransmitted to
Earth and picked up by
a receiver.
The ionosphere is
a layer of charged
particles, high in
the atmosphere.
Microwaves between
frequencies of 3GHz and
30GHz are used for
satellite communication
Below 3GHz, the waves are
reflected from the ionosphere
Above 30GHz the
waves are
scattered and
absorbed by the
atmosphere.
Long wavelength
radiowaves diffract around
hills, so have a longer
range.
F
Constructive interference: waves add
together to give a larger
wave;peak+peak or trough + trough;
waves are in phase.
Destructive interference: waves
subtract to give calm water/dark
area; peak + trough; waves
antiphase.
Lasers are used to show
interference, as they are coherent
(waves in phase), with same
wavelength /frequency.
Path difference is an even
number of
half-wavelengths in
constructive interference,
and odd number of half-
wavelengths in destructive
interference
Polarised light has
oscillations only in one plane.