### Revision videos

#### 3.2.1 Mechanics

**Scalars and vectors**

The addition of vectors by calculation or scale drawing. Calculations will be limited to two perpendicular vectors.

The resolution of vectors into two components at right angles to each other; examples should include the components of forces along and perpendicular to an inclined plane.

Conditions for equilibrium for two or three coplanar forces acting at a point; problems may be solved either by using resolved forces or by using a closed triangle.

**Moments**

Moment of a force about a point defined as force × perpendicular distance from the point to the line of action of the force; torque.

Couple of a pair of equal and opposite forces defined as force × perpendicular distance between the lines of action of the forces.

The principle of moments and its applications in simple balanced situations.

Centre of mass; calculations of the position of the centre of mass of a regular lamina are not expected.

**Motion along a straight line**

Displacement, speed, velocity and acceleration.

,

Representation by graphical methods of uniform and non-uniform acceleration; interpretation of velocity-time and displacement-time graphs for uniform and non-uniform acceleration; significance of areas and gradients.

Equations for uniform acceleration;

Acceleration due to gravity, *g*; detailed experimental methods of measuring *g* are

not required.

Terminal speed.

**Projectile motion**

Independence of vertical and horizontal motion; problems will be soluble from first principles. The memorising of projectile equations is not required.

**Newton’s laws of motion**

Knowledge and application of the three laws of motion in appropriate situations.

For constant mass, .

**Work, energy and power**

**Conservation of energy**

Principle of conservation of energy, applied to examples involving gravitational potential energy, kinetic energy and work done against resistive forces.

#### 3.2.2 Materials

**Bulk properties of solids
**Density

Hooke’s law, elastic limit, experimental investigations.

Tensile strain and tensile stress.

Elastic strain energy, breaking stress.

Derivation of

Description of plastic behaviour, fracture and brittleness; interpretation of simple stress-strain curves.

**The Young modulus**

One simple method of measurement.

Use of stress-strain graphs to find the Young modulus.

#### 3.2.3 Waves

**Progressive Waves**

Oscillation of the particles of the medium; amplitude, frequency, wavelength,

speed, phase, path difference.

**Longitudinal and transverse waves**

Characteristics and examples, including sound and electromagnetic waves.

Polarisation as evidence for the nature of transverse waves; applications e.g. Polaroid sunglasses, aerial alignment for transmitter and receiver.

**Refraction at a plane surface**

Refractive index of a substance s,

Candidates are not expected to recall methods for determining refractive indices.

Law of refraction for a boundary between two different substances of refractive indices and in the form

Total internal reflection including calculations of the critical angle at a boundary between a substance of refractive index and a substance of lesser refractive index or air;

Simple treatment of fibre optics including function of the cladding with lower refractive index around central core limited to step index only; application to communications.

**Superposition of waves, stationary waves
**The formation of stationary waves by two waves of the same frequency travelling in opposite directions; no mathematical treatment required.

Simple graphical representation of stationary waves, nodes and antinodes on strings.

**Interference
**The concept of path difference and coherence

The laser as a source of coherent monochromatic light used to demonstrate interference and diffraction; comparison with non-laser light; awareness of safety issues.

Candidates will not be required to describe how a laser works.

Requirements of two source and single source double-slit systems for the production of fringes.

The appearance of the interference fringes produced by a double slit system,

, where *s* is the slit separation

**Diffraction**

Appearance of the diffraction pattern from a single slit.

The plane transmission diffraction grating at normal incidence; optical details of the spectrometer will not be required.

Derivation of , where *n* is the order number.

Applications; e.g. to spectral analysis of light from stars.