MECHANICS, MATERIALS & WAVES PHYA2 Revision

for the AQA Unit 2 PHYA2 specification 

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MECANICS 7.1 ­ 8.8
MECHANICS
Scalars and vectors
· A scalar has only magnitude
o mass, temperature, time, length, speed and energy
· Vector quantities have both magnitude and direction
o displacement, force, velocity, acceleration and momentum
· Resultant Vectors
o Magnitude = Pythagoras
o Direction = Trigonometry
· Resolving Vectors
o Horizontal component = F x = F cos
o Vertical component = F v = F sin
Moments
The moment is the turning effect produced by a force:
o Moment of a force about a point (in N m) = force (N) x perpendicular distance from
the force to the point (m)
A couple is the turning effect due to two equal forces acting in the opposite direction:
o Couple (in N m) = magnitude of one force (N) x perpendicular distance between the
two forces in the couple (m)
The principle of moments states that, for an object in equilibrium:
o Sum of the clockwise moments about a point = sum of anti-clockwise moments
about that point.

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Page 2

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The centre of gravity of an object is the point at which its entire weight appears to act
An object will balance if supported at its centre of gravity
A freely suspended object will always come to rest with its centre of gravity directly below
the point of suspension.…read more

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If the object starts off at angle:
1. Resolve the initial velocity into vertical and horizontal components.
2. Use the vertical component to work out how high and long it is in the air for.
3. Use the horizontal component to work out how far it goes whilst it is in the air.
Terminal Velocity
Force of weight is equal to the force of air resistance so there is not net force and there is no
acceleration.…read more

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Velocity time graphs.
The gradient of a velocity time graph tells you the acceleration
The area under a speed time graph tells you the distance travelled
Constant acceleration is shown by a straight line
Decreasing acceleration if shown by a curve decreasing in gradient
Increasing acceleration is shown by a curve increasing in gradient
Mass, weight and centre of gravity
Weight is equal to mass times the force of gravity
Density is equal to mass divided by volume.…read more

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If object 1 exerts a force on object 2, then object 2 exerts an equal and opposite force on
object 1.
Car safety features designed to slow you down:
1. Seatbelts.
2. Airbags.
3. Crumple zones.
4. Safety cages.
Newton's third law Pairs
The two forces in a Newton pair always act on different objects
Each force in a Newton's third law pair must:
Be of the same magnitude, size.
o Act along the same line but in opposite directions.…read more

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Efficiency is equal to the useful energy or power output divided by the total energy or power input.
MATERIALS 11.1 ­ 11.4
MATERIALS
Hooke's Law
States that extension is proportional to force up to the elastic limit
Hooke's law: Force is equal to stiffness constant (k) times the extension (e).
Hooke's law works just as well for compressive as tensile forces
Plastic deformation: is when the material is permanently stretched.…read more

Page 7

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As you increase the tensile force the effect of the stress is to pull atoms apart. Eventually the
stress becomes so large the atom completely separate and the material breaks. On a stress,
strain graph this is the ultimate tensile stress point.
Elastic Strain energy is stored in a stretched material
Before the elastic limit, all the work done in stretching is stored as potential energy in the
material
This stored energy is called elastic strain energy.…read more

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Strong materials have a high breaking stress.
Elastic materials regains original dimensions when the deforming force is removed.
Interpreting stress strain graphs
Materials With a large gradient than another material is said to be stiffer
If the line suddenly stops before curving it means it has broke and therefore is brittle.
Whereas materials that curve undergo ductile flow before they break.
The area under a stress strain graph is the energy stored per unit volume. This area is a useful
measure of toughness.…read more

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Liquid: weigh in a measuring cylinder then minus the mass of the cylinder, then use equation
Irregular solid: Weigh, then immerse in water and measure increase in volume, then use
equation.
WAVES12.1 ­ 12.…read more

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Measuring Waves
Displacement - the distance and direction a particle moves from its equilibrium position.
Amplitude - the maximum displacement of a particle.
Wavelength - the distance between two adjacent vibrating particles.
Period - the time taken for one complete wave to pass a fixed point.
Frequency - the number of waves passing a given point every second.
The relationship between frequency and period is - time = 1/frequency.
The formula for the speed of a wave is -speed = frequency multiplied by wavelength.…read more

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