
Mechanics

Mechanics is the study of forces, energy and motion. In this module you will build on your work at GCSE and learn how to apply advanced mathematical techniques such as trigonometry and quadratic equations in order to solve problems. You will study the forces on objects that are not moving and are in equilibrium and you will also learn how to use the equations the describe objects that are moving with a constant acceleration. The ideas that you will learn in this module are fundamental to most advanced physics, and you will need to understand this in order to fully understand some of the Year 13 modules.

This is a very practical module; you will develop a lot of key skills such as how to reduce uncertainties through careful use and set-up of equipment. Most of the subjects within the module can be demonstrated with a practical. You can find links to most of the practical worksheets on this page. The module contains only one CAP, Finding g by freefall.

What you need to know

Below you can read exactly what AQA want you to know for this module. You can also find the relevant section from the specification on each page of this site. You should be aware of both what you need to know, and (just as importantly) what you DO NOT need to know. It is also important to remember that you need to be able to apply these statements to a wide range of different contexts, so you must practise this by attempting lots of different questions and reading around the subject.

3.4.1.1 Scalars and vectors

Nature of scalars and vectors.

Examples should include:
velocity/speed, mass, force/weight, acceleration, displacement/distance.

Addition of vectors by calculation or scale drawing.

Calculations will be limited to two vectors at right angles.

Scale drawings may involve vectors at angles other than 90°.

Resolution of vectors into two components at right angles to each other.

Examples should include components of forces along and perpendicular to an inclined plane.

Problems may be solved either by the use of resolved forces or the use of a closed triangle.

Conditions for equilibrium for two or three coplanar forces acting at a point. Appreciation of the meaning of equilibrium in the context of an object at rest or moving with constant velocity.

3.4.1.2 Moments

Moment of a force about a point.

Moment defined as:

force × perpendicular distance from the point to the line of action of the force.

Couple as a pair of equal and opposite coplanar forces.

Moment of couple defined as:

force × perpendicular distance between the lines of action of the forces.

Principle of moments.

Centre of mass.

Knowledge that the position of the centre of mass of uniform regular solid is at its centre.

3.4.1.3 Motion along a straight line

Displacement, speed, velocity, acceleration.

$$v=\frac{\Delta s}{\Delta t}$$ $$a=\frac{\Delta v}{\Delta t}$$

Calculations may include average and instantaneous speeds and velocities.

Representation by graphical methods of uniform and nonuniform acceleration.

Significance of areas of velocity–time and acceleration–time graphs and gradients of displacement–time and velocity–time graphs for uniform and non-uniform acceleration eg graphs for motion of bouncing ball.

Equations for uniform acceleration:

$$v=u+at$$ $$s=\frac{u+v}{2}t$$ $$s=ut+\frac{1}{2}at^{2}$$ $$v^{2}=u^{2}+2as$$

Acceleration due to gravity, g.

3.4.1.4 Projectile motion

Independent effect of motion in horizontal and vertical directions of a uniform gravitational field. Problems will be solvable using the equations of uniform acceleration.

Qualitative treatment of friction.

Distinctions between static and dynamic friction will not be tested.

Qualitative treatment of lift and drag forces.

Terminal speed.

Knowledge that air resistance increases with speed.

Qualitative understanding of the effect of air resistance on the trajectory of a projectile and on the factors that affect the maximum speed of a vehicle.

3.4.1.5 Newton’s laws of motion

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

$F = ma$ for situations where the mass is constant.

3.4.1.6 Momentum

$momentum=mass\times velocity$

Conservation of linear momentum.

Principle applied quantitatively to problems in one dimension.

Force as the rate of change of momentum,

$$F=\frac{\Delta \left (mv\right )}{\Delta t}$$

Impulse = change in momentum

$F\Delta t=\Delta mv$, where $F$ is constant.

Significance of the area under a force–time graph.

Quantitative questions may be set on forces that vary with time. Impact forces are related to contact times (eg kicking a football, crumple zones, packaging).

Elastic and inelastic collisions; explosions.

Appreciation of momentum conservation issues in the context of ethical transport design.

3.4.1.7 Work, energy and power

Energy transferred, $W=F\cos \theta$

rate of doing work = rate of energy transfer,$P=\frac{\Delta W}{\Delta t}=Fv$

Quantitative questions may be set on variable forces.

Significance of the area under a force–displacement graph.

$$\small efficiency=\frac{useful\: output\: power}{input\:power}$$

Efficiency can be expressed as a percentage.

3.4.1.8 Conservation of energy

Principle of conservation of energy.

$\Delta E_{p}=mg\Delta h$ and $E_{k}=\frac{1}{2}mv^{2}$

Quantitative and qualitative application of energy conservation to examples involving gravitational potential energy, kinetic energy, and work done against resistive forces.