Download P5 Key facts sheets: RAG - North Leamington School

P5 Key facts sheets:
Test Mark:
A: Satellites, Gravity and Circular Motion
Key Fact
Gravity is the universal force of attraction between masses
A satellite is an object that orbits a larger object in space
The Moon remains in orbit around the Earth and the Earth and other planets in orbit around
the Sun due to their gravitational attraction
The height above the Earth’s surface affects the orbit of an artificial satellite: The closer it
is, the faster it orbits.
Some of the applications of artificial satellites include: communications, weather forecasting,
military uses, scientific research, GPS, imaging the earth
Geostationary artificial satellites orbit the Earth once in 24 hours around the equator, remain
in a fixed position above the Earth’s Surface and orbit above the Earth’s equator
Circular motion requires a centripetal force. Gravity provides the centripetal force for orbital
motion
Artificial satellites are continually accelerating towards the Earth due to the Earth’s
gravitational pull, but their tangential motion keeps them moving in an approximately
circular orbit (H)
Artificial satellites in lower orbits travel faster than those in higher orbits because the
gravitational force of the Sun is greater (H)
The orbital period of planets increases the further they are from the Sun. This is in
part because they have further to travel due to a larger radius of orbit, but they also
travel more slowly due to the weaker centripetal/gravitational force of the Sun (H)
A periodic comet speeds up during its orbit around the Sun. The closer it gets, the
faster it moves due to the increasing gravitational force of the Sun. It’s distance from
the Sun varies because it has a highly elliptical orbit (H)
Gravitational force decreases with distance from an object. This is an inverse square law: if
the distance doubles, the force reduces by a factor of 4. If distance triples, force reduces
by a factor of 9 (H)
Ask yourself: Do I understand all of the summary facts? Do I need help? Write any
questions below. . . .
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Test Mark:
P5 Key facts sheet:
B: Vectors and Equations of Motion
Key Fact
Relative speed depends on the direction of movement (in context of two cars travelling on a
straight road)
Direction is not important when measuring speed, speed is a scalar quantity
The difference between scalar and vector quantities: some quantities (eg mass, time) are
scalar (no direction). Some quantities (eg force, velocity, acceleration) direction is important –
these are vectors
Vector sum from vector diagrams of parallel vectors: Where vectors point in the same
direction, add them. Where vectors point in opposite directions, subtract them.
For any journey the distance travelled can be calculated using the equation:
distance, s = average speed (u + v)/2 × time, t
s = (u + v)/2 x t
The equation: v = u + at can be used to calculate final speed, v, only (you need to be able to
rearrange these equations)
Calculating the resultant of two vectors that occur at right angles to each other can be
found using Pythagoras and trigonometry (H) Learn these methods!:
Use the equations v2 = u2 + 2as, s = ut + 1 /2at2 (including change of subject) to find (H):
final velocity, v
initial velocity, u
distance, s
acceleration, a
time, t
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questions below. . . .
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Test Mark:
P5 Key facts sheet:
C: Projectile Motion
Key Fact
The path of an object projected horizontally in the Earth’s gravitational field is curved. This
path is called a trajectory, e.g. a bullet from a gun, a ball being thrown (horizontally)
The shape of this trajectory is parabolic
The range (distance travelled) of a ball struck in sport depends on the launch angle, with an
optimum angle of 45°
Other than air resistance, the only force acting on a ball during flight is gravity
Projectiles have a downward acceleration and this only affects the vertical velocity, not
horizontal velocity
For a projectile in Earth's gravitational field (we normally ignore air resistance)
• there is no acceleration in the horizontal direction (a constant horizontal
velocity)
• the acceleration due to gravity, g, acts in the vertical direction (steadily
increasing vertical velocity)
The horizontal and vertical velocities of a projectile are vectors
The resultant velocity of a projectile is the vector sum of the horizontal and vertical
velocities (H)
For an object projected horizontally:
• the horizontal velocity is unaffected by gravity
• therefore the horizontal velocity is constant
•but, gravity causes the vertical velocity to change (H)
You must practice using the equations of motion (in Item P5b) for an object projected
horizontally above the Earth's surface where the gravitational field is uniform (H)
Ask yourself: Do I understand all of the summary facts? Do I need help? Write any
questions below. . . .
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P5 Key facts sheet:
D: Collisions, momentum and gases
Key Fact
Newton’s Third Law: every action has an equal and opposite reaction
Everyday examples of collisions include sporting examples (kicking a ball, or hitting a gold
ball) and car collisions
When an object collides with another object or two bodies interact, the two objects exert an
equal and opposite force on each other (Newton III)
Opposite reactions in static (non-moving) situations include the interaction between you and
the Earth: You pull the Earth towards you; you are also pulled equally towards the Earth due
to gravity
Gases exert a pressure on the walls of their container. In a space rocket, the force pushing
the particles backwards equals the force pushing the rocket forwards
Changes in volume or temperature produce a change in pressure in a gas. Increasing the
volume of a container with the same amount of gas reduces pressure; increasing the
temperature of a gas increases pressure as the particles have more kinetic energy
Pressure can be explained in terms of (H):
• the change of momentum of the particles striking the walls creating a force
• the frequency of collisions with the walls of the container increasing
For large scale rockets used to lift satellites into the Earth’s orbit, sufficient force is
created to lift the rocket by (H):
• using a large number of particles of exhaust gas
• the particles must be moving at high speeds to generate large forces (H)
The principle of conservation of momentum can be used to describe the collision between
two objects moving in the same direction, for collisions when the colliding objects
coalesce (join together) using the equation (H):
m1 u1 + m2 u2 = (m1 + m2) v
Momentum is a property that is always conserved and can be used to explain:
• explosions
• recoil
• rocket propulsion (H) (you need to be able to explain this!)
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questions below. . . .
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P5 Key facts sheet:
E: Satellite Communication
Key Fact
Different frequency waves are used for low orbit satellites (relatively lower frequency) and
geostationary satellites (relatively higher frequency)
Some radio waves (e.g. long wavelength) are reflected by part of the Earth’s upper
atmosphere
Some radio waves (e.g. short wavelength) and microwaves pass through the Earth’s
atmosphere
Information can be transmitted using microwaves to orbiting artificial satellites and then
retransmitted back to Earth or to other satellites
Electromagnetic waves with different frequencies behave differently in the atmosphere:
• below 30 MHz are reflected by the ionosphere
• above 30 GHz, rain, dust and other atmospheric effects reduce the strength of
the signal due to absorption and scattering
• between 30 MHz and 30 GHz can pass through the Earth’s atmosphere
Radio waves have a very long wavelength and can ‘spread’ around large objects. This is called
diffraction. It enables radio signals to be received by people living in hilly areas, as the waves
will diffract around the hills.
Satellite transmitting and receiving dishes need very careful alignment:
• the size of a satellite communication dish is many times the microwave
wavelength
• this produces little diffraction hence a narrow beam that does not spread
out
• this means the receiving dish and satellite need exact alignment (H)
The amount of diffraction of a wave depends upon the size of the gap and the
wavelength of the wave. The conditions of maximum diffraction are when a wave passes
through a gap most similar in size to its wavelength (H)
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questions below. . . .
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P5 Key facts sheet:
F: Nature of Waves
Key Fact
Interference occurs when two waves overlap. When waves overlap there are areas where the
waves add together and areas where the waves subtract from each other
The effect of interference on waves can be observed in sound (two speakers), light
(diffraction through 2 slits) and water (2 waves on a ripple tank).
You need to be able to describe the interference of two waves, using one of the above
examples, in terms of reinforcement and cancellation of the waves
Coherent waves sources are needed to produce a stable interference pattern. For light, this
means you need a monochromatic (one wavelength) source
Light travels in straight lines. Evidence to support this includes e.g. shadows and eclipses
All electromagnetic waves are transverse
Light diffracts through a single slit and double slits. In both cases a fringe pattern is
produced (look this up in your revision guide).The interference patterns produced are
evidence of the wave nature of light.
All e-m waves are transverse waves and therefore can be plane polarised
Explanations of the nature of light have changed over time, with some scientists describing
light as waves, and some scientists describing light as particles. Reflection of light can easily
be described by a particle model (like a ball bouncing off a surface)
The particle theory of light is not universally accepted, because diffraction, polarisation and
interference patterns are better explained using a wave model
Interference patterns: Constructive interference occurs when two waves are in phase (crest
meets crest). Destructive interference occurs when two waves are in anti-phase (crest meets
trough) (H)
The number of half wavelengths in the path difference for two waves from the same source
relates to the type of interference caused (H):
• Constructive Interference: path difference = nλ
• Destructive interference: path difference = (n + ½)λ
(n = 0,1,2 etc)
Coherent wave sources have the same frequency, they have a constant phase difference &
the same amplitude (H)
Polarisation is used in Polaroid filters and sunglasses. Light from some substances (e.g. water
or snow) is partly polarised in parallel to the surface it is reflecting from (e.g. horizontally).
Polaroid filters in this case will be vertically polarised to block out the horizontally polarised
light (H)
Wave theory of light has surpassed particle theory, as the evidence base has changed over
time from things like Young’s Double Slit Experiment (H)
Ask yourself: Do I understand all of the summary facts? Do I need help? Write any
questions below. . . .
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Test Mark:
P5 Key facts sheet:
G: Refraction of Waves
Key Fact
Refraction involves a change in direction of a wave due to the wave passing from one medium
into another
A ray of light travelling from air into glass has an angle of incidence usually greater than the
angle of refraction, because light refracts towards the normal when it enters a medium of
higher density
Refraction occurs at the boundary between two media: when the wave speed decreases the
wave bends towards the normal; when the wave speed increases the wave bends away from the
normal
Refractive index is a measure of the amount of refraction after a boundary
Refractive index = c ÷ v (where c = speed of light in a vacuum, v = speed of light in the
medium. e.g. glass)
Dispersion happens when light is refracted. This is where refraction splits light into all the
spectral colours and the amount of refraction for each colour depends on its wavelength
The amount of bending (refraction) increases with greater change of wave speed and
refractive index
Dispersion can be explained in terms of spectral colours having different wave speeds in
different media but the same speeds in a vacuum
Some, or all, of a light ray can be reflected when travelling from glass, or water, to air.
There are many uses of Total Internal Reflection (TIR), including: optical fibres; binoculars;
reflectors and cat’s eyes on the road and road signs
Light incident on a glass/air surface: will refract when the angle of incidence is less than the
critical angle; will refract at 90° when angle of incidence is equal to critical angle; will TIR
when the angle of incidence is above the critical angle
Different media (e.g. glass, air, water, diamond) have different critical angles
Refractive index = c ÷ v. This will require the use of standard form notation (e.g. 3 x
1 08 m/s) and/or a scientific notation calculator. (H)
Dispersion occurs because spectral colours have a different speed in glass (if a glass
prism is being used), and different refractive indices; blue light having a greater
refractive index than red light so blue bends the most (H)
The larger the refractive index, the smaller the critical angle. This is why diamonds
sparkle so much – more light is totally internally reflected! (H)
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questions below. . . .
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Test Mark:
P5 Key facts sheet:
H: Optics
Key Fact
Convex lenses are also called converging lenses. They are fat in the middle & thin at the edge
Light incident on a convex lens parallel to the axis will converge/focus at the focal point
The focal length of a convex lens is measured from the centre of the lens to the focal point
‘fat’ lenses have short focal lengths and ‘thin’ lenses have long focal lengths
The effect of a convex lens on a diverging beam of light is that it will focus the light at a
point behind the focal point:
This diagram shows the
light diverging (spreading
out)
Key terms:
Convex lenses produce real images on a screen
Revise your ray diagrams to show how a convex lens produces a real image on film and screen
respectively (A suitable diagram may be required or given)!
Convex lenses are used: in cameras; in projectors; in some spectacles; as a magnifying glass
Images produced by cameras and projectors are focused by changing the distance between
the lens and the screen. This depends on how far away the object is – you need to revise this
magnification = image size ÷ object size
Real images: are inverted and can be projected on to a screen (H)
Virtual images: are upright and cannot be projected onto a screen (H)
Revise how to find the position and size of the real image formed by a convex lens by
drawing suitable ray diagrams (H)!
Including a change of subject: magnification = image size ÷ object size (H)
Ask yourself: Do I understand all of the summary facts? Do I need help? Write any
questions below. . . .
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