# Credit

This unit is worth 90 UMS, which equates to 30% of the AS credit or 15% of the A2 credit.

# Assessment

It is examined by a single 60-mark 1 hour written exam in either January or May/June.

# Content

## Module 1 : Motion

*This module provides knowledge and understanding of key ideas used to describe the motion of objects. The module is essential in the understanding of safety features of cars covered in the* Forces in Action *module. It also provides students with opportunities to develop both analytical and experimental skills. The motion of a variety of objects can be analysed using graphical, ICT or data-logging techniques. The work of Galileo on falling objects can be used to illustrate how scientific ideas are modified and also the tentative nature of scientific knowledge.*

**Physical quantities and units**

*Candidates should be able to:*

- explain that some physical quantities consist of a numerical magnitude and a unit;
- use correctly the named units listed in this specification as appropriate;
- use correctly the following prefixes and their symbols to indicate decimal sub-multiples or multiples of units: pico (p), nano (n), micro (μ), milli (m), centi (c), kilo (k), mega (M), giga (G), tera (T);
- make suitable estimates of physical quantities included within this specification.

**Scalars and vectors**

*Candidates should be able to:*

- define scalar and vector quantities and give examples;
- draw and use a vector triangle to determine the resultant of two coplanar vectors such as displacement, velocity and force;
- calculate the resultant of two perpendicular vectors such as displacement, velocity and force;
- resolve a vector such as displacement, velocity and force into two perpendicular components.

**Kinematics**

*Candidates should be able to:*

- define displacement, instantaneous speed, average speed, velocity and acceleration;
- select and use the relationships average speed = distance / time, acceleration = change in velocity /time to solve problems;
- apply graphical methods to represent displacement, speed, velocity and acceleration;
- determine velocity from the gradient of a displacement against time graph;
- determine displacement from the area under a velocity against time graph;
- determine acceleration from the gradient of a velocity against time graph.

**Linear motion**

*Candidates should be able to:*

- derive the equations of motion for constant acceleration in a straight line from a velocity against time graph;
- Select and use the equations of motion for constant acceleration in a straight line:

v = u + at

s = $\frac{1}{2}$(u + v)t

s = ut + $\frac{1}{2}$at^{2} and

v^{2} = u^{2} + 2as ;

- apply the equations for constant acceleration in a straight line, including the motion of bodies falling in the Earth’s uniform gravitational field without air resistance;
- explain how experiments carried out by Galileo overturned Aristotle’s ideas of motion;
- describe an experiment to determine the acceleration of free fall g using a falling body;
- apply the equations of constant acceleration to describe and explain the motion of an object due to a uniform velocity in one direction and a constant acceleration in a perpendicular direction.

## Module 2 : Forces in Motion

*What happens when several forces act on an object? This important question is of paramount importance to a civil engineer building a bridge or to a car designer aiming to break the world speed record. The material covered in this and the earlier module on motion is used to understand the safety features and navigation systems (GPS) used in modern cars. There are opportunities for students to appreciate societal benefits from scientific innovations. The work of Newton on the motion of objects can be used to illustrate how scientific ideas need to be modified and also the tentative nature of scientific knowledge.*

**Force**

*Candidates should be able to:*

- Solve problems using the relationship: net force = mass × acceleration (F = ma) appreciating that acceleration and the net force are always in the same direction;
- define the newton;
- apply the equations for constant acceleration and F = ma to analyse the motion of objects;
- recall that according to the special theory of relativity, F = ma cannot be used for a particle travelling at very high speeds because its mass increases.

**Non-linear motion**

*Candidates should be able to:*

- explain that an object travelling in a fluid experiences a resistive or a frictional force known as drag;
- state the factors that affect the magnitude of the drag force;
- determine the acceleration of an object in the presence of drag;
- state that the weight of an object is the gravitational force acting on the object;
- select and use the relationship: weight = mass × acceleration of free fall (W = mg);
- describe the motion of bodies falling in a uniform gravitational field with drag;
- use and explain the term terminal velocity.

**Equilibrium**

*Candidates should be able to:*

- draw and use a triangle of forces to represent the equilibrium of three forces acting at a point in an object;
- state that the centre of gravity of an object is a point where the entire weight of an object appears to act;
- describe a simple experiment to determine the centre of gravity of an object;
- explain that a couple is a pair of forces that tends to produce rotation only;
- define and apply the torque of a couple;
- define and apply the moment of force;
- explain that both the net force and net moment on an extended object in equilibrium is zero;
- apply the principle of moments to solve problems, including the human forearm;
- select and use the equation for density: ρ = m/V;
- select and use the equation for pressure p = F/A where F is the force normal to the area A.

**Car safety**

*Candidates should be able to:*

- define thinking distance, braking distance and stopping distance;
- analyse and solve problems using the terms thinking distance, braking distance and stopping distance;
- describe the factors that affect thinking distance and braking distance;
- describe and explain how air bags, seat belts and crumple zones in cars reduce impact forces in accidents;
- describe how air bags work, including the triggering mechanism;
- describe how the trilateration technique is used in GPS (global positioning system) for cars.

## Module 3 : Work and Energy

*Words like energy, power and work have very precise interpretation in physics. In this module the important link between work and energy is explored. The important principle of conservation of energy is applied to a range of situations including a rollercoaster. All around us we have building structures under tension or compression. Such forces alter the shape and dimensions of objects. If the force per unit area for a particular material exceeds a certain value, then there is a danger of the material breaking apart and this is the last thing an engineer would want. Using the appropriate materials in construction is important. In this module we explore the properties of materials.*

**Work and conservation of energy**

*Candidates should be able to:*

- define work done by a force;
- define the joule;
- calculate the work done by a force using W = Fx and W = Fx cos θ;
- state the principle of conservation of energy;
- describe examples of energy in different forms, its conversion and conservation, and apply the principle of energy conservation to simple examples;
- apply the idea that work done is equal to the transfer of energy to solve problems.

**Kinetic and potential energies**

*Candidates should be able to:*

- select and apply the equation for kinetic energy E = $\frac{1}{2}$mv
^{2}; - apply the definition of work done to derive the equation for the change in gravitational potential energy;
- select and apply the equation for the change in gravitational potential energy near the Earth’s surface E
_{p}= mgh; - analyse problems where there is an exchange between gravitational potential energy and kinetic energy;
- apply the principle of conservation of energy to determine the speed of an object falling in the Earth’s gravitational field.

**Power**

*Candidates should be able to:*

- define power as the rate of work done;
- define the watt;
- calculate power when solving problems;
- state that the efficiency of a device is always less than 100% because of heat losses;
- select and apply the relationship for efficiency: efficiency = $\frac{useful output energy}{total input energy}$ × 100%;
- interpret and construct Sankey diagrams.

**Behaviour of springs and materials**

*Candidates should be able to:*

- describe how deformation is caused by a force in one dimension and can be tensile or compressive;
- describe the behaviour of springs and wires in terms of force, extension, elastic limit, Hooke’s law and the force constant (ie force per unit extension or compression);
- select and apply the equation F = kx, where k is the force constant of the spring or the wire;
- determine the area under a force against extension (or compression) graph to find the work done by the force;
- select and use the equations for elastic potential energy: E = $\frac{1}{2}$Fx and E = $\frac{1}{2}$kx
^{2}; - define and use the terms stress, strain, Young modulus and ultimate tensile strength (breaking stress);
- describe an experiment to determine the Young modulus of a metal in the form of a wire;
- define the terms elastic deformation and plastic deformation of a material;
- describe the shapes of the stress against strain graphs for typical ductile, brittle and polymeric materials.

# Past exam questions

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