GCSE Science₈₄₆₅

Recall examples of ways in which objects interact: by gravity, electrostatics, magnetism and by contact (including normal contact force and friction), and describe how such examples involve interactions between pairs of objects which produce a force on each object, representing such forces as vectors.

Scalar quantities have magnitude only. Vector quantities have magnitude and an associated direction.

Force is a vector quantity.

A vector quantity may be represented by an arrow. The length of the arrow represents the magnitude, and the direction of the arrow the direction of the vector quantity.

A force is a push or pull that acts on an object due to the interaction with another object. All forces between objects are either:

• contact forces – the objects are physically touching

or

• non-contact forces – the objects are physically separated.

Describe examples of the forces acting on an isolated solid object or system; describe, using free body diagrams, examples where several forces lead to a resultant force on an object and the special case of balanced forces when the resultant force is zero (qualitative only).

A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together. This single force is called the resultant force.

A free body diagram shows the magnitude and direction of the forces acting on an object.

A single force can be resolved into two components acting at right angles to each other. The two component forces together have the same effect as the single force.

WS 1.2, MS 4a, 5a, 5b

Use vector diagrams to illustrate resolution of forces and equilibrium situations and determine the resultant of two forces, to include both magnitude and direction (scale drawings only).

Describe and calculate the changes in energy involved when a system is changed by the work done by forces acting upon it.

Use the relationship between work done, force and distance moved along the line of action of the force, describing the energy transfer involved.

A force does work on an object when the force causes a displacement of the object.

$\mathit{w}\mathit{o}\mathit{r}\mathit{k}\mathit{ }\mathit{d}\mathit{o}\mathit{n}\mathit{e}\mathit{ }\mathsf{=}\mathit{f}\mathit{o}\mathit{r}\mathit{c}\mathit{e}\mathit{ }\mathsf{\times }\mathit{d}\mathit{i}\mathit{s}\mathit{t}\mathit{a}\mathit{n}\mathit{c}\mathit{e}\mathit{ }\mathsf{\left(}\mathit{m}\mathit{o}\mathit{v}\mathit{e}\mathit{d}\mathit{ }\mathit{a}\mathit{l}\mathit{o}\mathit{n}\mathit{g}\mathit{ }\mathit{t}\mathit{h}\mathit{e}\mathit{ }\mathit{l}\mathit{i}\mathit{n}\mathit{e}\mathit{ }\mathit{o}\mathit{f}\mathit{ }\mathit{a}\mathit{c}\mathit{t}\mathit{i}\mathit{o}\mathit{n}\mathit{ }\mathit{o}\mathit{f}\mathit{ }\mathit{t}\mathit{h}\mathit{e}\mathit{ }\mathit{f}\mathit{o}\mathit{r}\mathit{c}\mathit{e}\mathsf{\right)}$

$\mathsf{[}\mathit{ }\mathit{W}\mathit{ }\mathsf{=}\mathit{F}\mathit{ }\mathit{s}\mathit{ }\mathsf{]}$

work done, W , in joules, J

force, F , in newtons, N

distance, s , in metres

One joule of work is done when a force of one newton causes a displacement of one metre.

1 joule = 1 newton-metre

WS 1.2, MS 3b, 3c

Recall and apply this equation to calculate energy transfers.

WS 4.5, MS 1c, 3c

Convert between newton-metres and joules.

Define weight, describe how it is measured and describe the relationship between the weight of that body and the gravitational field strength.

Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth.

The weight of an object depends on the gravitational field strength at the point where the object is:

$\mathit{w}\mathit{e}\mathit{i}\mathit{g}\mathit{h}\mathit{t}\mathit{ }\mathsf{=}\mathit{m}\mathit{a}\mathit{s}\mathit{s}\mathit{ }\mathsf{\times }\mathit{g}\mathit{r}\mathit{a}\mathit{v}\mathit{i}\mathit{t}\mathit{a}\mathit{t}\mathit{i}\mathit{o}\mathit{n}\mathit{a}\mathit{l}\mathit{ }\mathit{f}\mathit{i}\mathit{e}\mathit{l}\mathit{d}\mathit{ }\mathit{s}\mathit{t}\mathit{r}\mathit{e}\mathit{n}\mathit{g}\mathit{t}\mathit{h}$

$\mathsf{[}\mathit{ }\mathit{W}\mathit{ }\mathsf{=}\mathit{m}\mathit{ }\mathit{g}\mathit{ }\mathsf{]}$

weight, W , in newtons , N

mass, m , in kilograms, kg

gravitational field strength, g , in newtons per kilogram, N/kg

The weight of an object and the mass of an object are directly proportional.

Weight is measured using a calibrated spring balance (a newtonmeter ).

WS 1.2, MS 3b, 3c

Recall and apply this equation.

In any calculation the value of the gravitational field strength ( g ) will be given.

MS 3a

Understand and use the symbol for proportionality, ∝

Calculate the amounts of energy associated with an object raised above ground level.

An object raised above ground level gains gravitational potential energy

$\mathit{g}\mathsf{.}\mathit{p}\mathsf{.}\mathit{e}\mathsf{.}\mathit{ }\mathsf{=}\mathit{m}\mathit{a}\mathit{s}\mathit{s}\mathit{ }\mathsf{\times }\mathit{g}\mathit{r}\mathit{a}\mathit{v}\mathit{i}\mathit{t}\mathit{a}\mathit{t}\mathit{i}\mathit{o}\mathit{n}\mathit{a}\mathit{l}\mathit{ }\mathit{f}\mathit{i}\mathit{e}\mathit{l}\mathit{d}\mathit{ }\mathit{s}\mathit{t}\mathit{r}\mathit{e}\mathit{n}\mathit{g}\mathit{t}\mathit{h}\mathit{ }\mathsf{\times }\mathit{h}\mathit{e}\mathit{i}\mathit{g}\mathit{h}\mathit{t}$

$$ ${\mathit{E}}_{\mathit{p}}\mathit{ }\mathit{ }\mathsf{=}\mathit{m}\mathit{ }\mathit{g}\mathit{ }\mathit{h}$

gravitational potential energy, E _p , in joules, J

mass, m , in kilograms, kg

gravitational field strength, g , in newtons per kilogram, N/kg

height, h , in metres, m

WS 1.2, MS 3c

Recall and apply this equation to calculate changes in stored energy.

In any calculation the value of the gravitational field strength ( g ) will be given.

Explain, with examples, that to stretch, bend or compress an object, more than one force has to be applied.

Describe the difference between elastic and inelastic distortions caused by stretching forces; describe the relationship between force and extension for a spring and other simple systems; describe the difference between linear and non-linear relationships between force and extension, and calculate a spring constant in linear cases.

An object that has been stretched has been elastically deformed if the object returns to its original length after the forces are removed. An object that does not return to its original length after the forces have been removed has been inelastically deformed.

The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

force = spring constant x extension

[ F = k e ]

force, F, in newtons, N

spring constant, k, in newtons per metre, N/m

extension, e, in metres, m

A force that stretches (or compresses) a spring does work, and elastic potential energy is stored in the spring. Provided the spring does not go past the limit of proportionality the work done on the spring and the elastic potential energy stored are equal.

WS 1.2, MS 3c, 4a, 4b, 4c

Recall and apply this equation

Calculate the amounts of energy associated with a stretched spring.

Elastic potential energy is stored in a stretched spring.

$\mathit{e}\mathit{l}\mathit{a}\mathit{s}\mathit{t}\mathit{i}\mathit{c}\mathit{ }\mathit{p}\mathit{o}\mathit{t}\mathit{e}\mathit{n}\mathit{t}\mathit{i}\mathit{a}\mathit{l}\mathit{ }\mathit{e}\mathit{n}\mathit{e}\mathit{r}\mathit{g}\mathit{y}\mathit{ }\mathsf{=}\mathsf{0.5}\mathit{ }\mathsf{\times }\mathit{s}\mathit{p}\mathit{r}\mathit{i}\mathit{n}\mathit{g}\mathit{ }\mathit{c}\mathit{o}\mathit{n}\mathit{s}\mathit{t}\mathit{a}\mathit{n}\mathit{t}\mathit{ }\mathsf{\times }\mathsf{(}\mathit{e}\mathit{x}\mathit{t}\mathit{e}\mathit{n}\mathit{s}\mathit{i}\mathit{o}\mathit{n}{\mathsf{)}}^{\mathsf{2}}$

${\mathsf{[}\mathit{E}}_{\mathit{e}}\mathit{ }\mathit{ }\mathsf{=}\mathit{ }\frac{\mathsf{1}}{\mathsf{2}}\mathit{ }\mathit{k}\mathit{ }{\mathit{e}}^{\mathsf{2}}\mathsf{]}$

(assuming the limit of proportionality has not been exceeded)

elastic potential energy, E _e , in joules, J

spring constant, k , in newtons per metre, N/m

extension, e , in metres, m

WS 1.2, MS 1c, 3c

Calculate the work done in stretching.

MS 3b, 3c

Apply this equation, which is given on the Physics equations sheet.

Describe and compare the nature and arrangement of chemical bonds in ionic compounds, simple molecules, giant covalent structures, and polymers and metals.

There are three types of strong chemical bonds: ionic, covalent and metallic.

For ionic bonding the particles are oppositely charged ions.

For covalent bonding the particles are atoms that share pairs of electrons.

For metallic bonding the particles are atoms that share delocalised electrons.

Ionic bonding occurs in compounds formed from metals combined with non-metals.

Covalent bonding occurs in non-metallic elements and in compounds of non-metals.

Metallic bonding occurs in metallic elements and alloys.

Construct dot and cross diagrams for simple ionic substances.

Deduce the empirical formula of a compound from the relative numbers of atoms present or from a model or diagram and vice versa.

Use the formulae of common ions to deduce the formula of a compound.

When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred. Metal atoms lose electrons to become positively charged ions. Non-metal atoms gain electrons to become negatively charged ions. The ions produced by metals in groups 1 and 2 and by non-metals in groups 6 and 7 have the electronic structure of a noble gas (Group 0).

The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, eg for sodium chloride:

The charge on the ions produced by metals in groups 1 and 2 and by non-metals in groups 6 and 7 relates to the group number of the element in the periodic table.

An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.

The structure of sodium chloride can be represented in the following forms:

Knowledge of the structures of specific ionic compounds other than sodium chloride is not required.

WS 1.2

Draw dot and cross diagrams for ionic compounds formed by metals in groups 1 and 2 with non-metals in groups 6 and 7.

Work out the charge on the ions of metals and non-metals from the group number of the element, limited to the metals in groups 1 and 2, and non-metals in groups 6 and 7.

Describe the limitations of particular representations and models to include dot and cross diagrams, ball and stick models and two- and three-dimensional representations.

MS 4a

Translate data between diagrammatic and numeric forms.

MS 5b

Draw or complete diagrams to represent 2D and 3D forms including two-dimensional representations of 3D structures.

MS 1a

Use arithmetic computation and ratio when determining empirical formulae.

Explain how the bulk properties of materials are related to the different types of bonds they contain, their bond strengths and the ways in which their bonds are arranged, recognising that the atoms themselves do not have these properties.

Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.

These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.

WS 1.2

Use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur.

Use data to predict states of substances under given conditions.

Explain chemical bonding in terms of electrostatic forces and the sharing of electrons.

Construct dot and cross diagrams for simple covalent substances.

Deduce the empirical formula of a compound from the relative numbers of atoms present or from a model or diagram and vice versa.

When atoms share pairs of electrons they form covalent bonds. These bonds between atoms are strong.

Covalently bonded substances may consist of small molecules.

Some covalently bonded substances have very large molecules, such as polymers.

Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.

The covalent bonds in molecules and giant structures can be represented in the following forms:

Polymers can be represented in the form:

where n is a large number.

WS 1.2

Recognise substances as small molecules, polymers or giant structures from diagrams showing their bonding.

Draw dot and cross diagrams for the molecules of hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia and methane.

Represent the covalent bonds in small molecules, in the repeating units of polymers and in part of giant covalent structures, using a line to represent a single bond.

Describe the limitations of particular representations and models to include dot and cross diagrams, ball and stick models and two- and three-dimensional representations.

MS 5b

Draw or complete diagrams to represent 2D and 3D forms including two-dimensional representations of 3D molecules.

MS 1a

Use arithmetic computation and ratio when determining empirical formulae.

Explain how the bulk properties of materials are related to the different types of bonds they contain, their bond strengths in relation to intermolecular forces and the ways in which their bonds are arranged, recognising that the atoms themselves do not have these properties.

Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points.

These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.

These substances do not conduct electricity because the molecules do not have an overall electric charge.

Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

Substances that consist of giant covalent structures are solids with very high melting points. All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures.

WS 1.2

Use the idea that intermolecular forces are weak compared with covalent bonds to explain the bulk properties of molecular substances.

Use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur.

Recognise polymers from diagrams showing their bonding.

Recognise giant covalent structures from diagrams showing their bonding.

Use data to predict states of substances under given conditions.

Explain chemical bonding in terms of electrostatic forces and the sharing of electrons.

Metals consist of giant structures of atoms arranged in a regular pattern.

The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds. The bonding in metals may be represented in the following form:

MS 5b

Draw or complete diagrams to represent 2D and 3D forms including two-dimensional representations of 3D structures.

Explain how the bulk properties of materials are related to the different types of bonds they contain, their bond strengths and the ways in which their bonds are arranged, recognising that the atoms themselves do not have these properties.

Metals have giant structures of atoms with strong metallic bonding. This means that most metals have high melting and boiling points.

The layers of atoms in a metal crystal can slide over each other. This means metals can be bent and shaped.

Pure metals are too soft for many uses and so are mixed with other metals to make alloys.

The different sizes of atoms in an alloy distort the crystal structure, making alloys harder than pure metals.

Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal.

WS 1.2

Use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur.

Use data to predict states of substances under given conditions.

Describe the attraction and repulsion between unlike and like poles for permanent magnets and describe the difference between permanent and induced magnets.

The poles of a magnet are the places where the magnetic forces are strongest. When two magnets are brought close together they exert a force on each other. Attraction and repulsion between two magnetic poles are examples of non-contact force.

A permanent magnet produces its own magnetic field. An induced magnet is a material that becomes a magnet when it is placed in a magnetic field. Induced magnetism always causes a force of attraction. When removed from the magnetic field an induced magnet loses most/all of its magnetism quickly.

Describe the characteristics of the magnetic field of a magnet, showing how strength and direction change from one point to another.

The region around a magnet where a force acts on another magnet or on a magnetic material (iron, steel, cobalt and nickel) is called the magnetic field.

The force between a magnet and a magnetic material is always one of attraction.

The strength of the magnetic field depends on the distance from the magnet. The field is strongest at the poles of the magnet.

The direction of the magnetic field at any point is given by the direction of the force that would act on another north pole placed at that point. The direction of a magnetic field line is from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet.

WS 2.2

Draw the magnetic field pattern of a bar magnet and describe how to plot the magnetic field pattern using a compass.

Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.

A magnetic compass contains a small bar magnet. The Earth has a magnetic field. The compass needle points in the direction of the Earth’s magnetic field.

The Earth’s magnetic field is probably caused by movements in the liquid, iron-rich part of the outer core of the Earth. The slow changes to the positions of the magnetic north and south poles, and the way that the field reverses its direction from time to time, show that the magnetism of the core is dynamic and not static. The intervals between reversals are not uniform. The last reversal happened about 800,000 years ago.

WS 1.3

Explain why the data needed to answer a scientific question, in a given context, may not be available because of matters of scale and complexity.

Describe how to show that a current can create a magnetic effect and describe the directions of the magnetic field around a conducting wire.

When a current flows through a conducting wire a magnetic field is produced around the wire. The shape of the magnetic field can be seen as a series of concentric circles in a plane perpendicular to the wire. The direction of these field lines depends on the direction of the current.

WS 1.2, 3.1

Draw the magnetic field pattern for a straight wire carrying a current (showing the direction of the field).

WS 1.2

Use the 'right-hand grip rule' to predict the direction of the field.

Recall that the strength of the field depends on the current and the distance from the conductor, and explain how solenoid arrangements can enhance the magnetic effect.

The strength of the magnetic field depends on the current through the wire and the distance from the wire.

Shaping a wire to form a solenoid increases the strength of the magnetic field created by a current through the wire. The magnetic field inside a solenoid is strong and uniform.

The magnetic field around a solenoid has a similar shape to that of a bar magnet. Adding an iron core increases the magnetic field strength of a solenoid. An electromagnet is a solenoid with an iron core.

WS 3.1

Draw the magnetic field pattern for a solenoid carrying a current (showing the direction of the field).

WS 1.4

Compare the advantages and disadvantages of permanent and electromagnets for particular uses.

Describe how a magnet and a current-carrying conductor exert a force on one another and show that Fleming’s left-hand rule represents the relative orientations of the force, the conductor and the magnetic field.

When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other. This is called the motor effect.

The direction of the force on the conductor is reversed if either the direction of the current or the direction of the magnetic field is reversed.

WS 1.2

Use Fleming’s left-hand rule to predict the direction of the force on a conductor.

Apply the equation that links the force on a conductor to the magnetic flux density, the current and the length of conductor to calculate the forces involved.

The size of the force on the conductor depends on:

• the magnetic flux density
• the current in the conductor
• the length of conductor in the magnetic field.

For a conductor at right angles to a magnetic field and carrying a current:

$\mathit{f}\mathit{o}\mathit{r}\mathit{c}\mathit{e}\mathit{ }\mathsf{=}\mathit{m}\mathit{a}\mathit{g}\mathit{n}\mathit{e}\mathit{t}\mathit{i}\mathit{c}\mathit{ }\mathit{f}\mathit{l}\mathit{u}\mathit{x}\mathit{ }\mathit{d}\mathit{e}\mathit{n}\mathit{s}\mathit{i}\mathit{t}\mathit{y}\mathit{ }\mathsf{\times }\mathit{c}\mathit{u}\mathit{r}\mathit{r}\mathit{e}\mathit{n}\mathit{t}\mathit{ }\mathsf{\times }\mathit{l}\mathit{e}\mathit{n}\mathit{g}\mathit{t}\mathit{h}$ $$

$\mathsf{[}\mathit{F}\mathit{ }\mathsf{=}\mathit{B}\mathit{ }\mathit{I}\mathit{ }\mathrm{l}\mathsf{}\mathsf{]}$

force, F , in newtons, N

magnetic flux density, B , in tesla, T

current, I , in amperes, A (amp is acceptable for ampere)

length, l , in metres, m

MS 3c

Apply this equation, which is given on the Physics equations sheet.

WS 3.3

Carry out and represent mathematical and statistical analysis.

Explain how this force is used to cause rotation in electric motors.

A simple electric motor consists of a rectangular coil of wire that is free to turn in the magnetic field of a permanent magnet. A commutator reverses the direction of the current every half turn, to allow the rotation to continue.

WS 1.2

Apply Fleming’s left-hand rule to a simple electric motor.

WS 1.4

Explain everyday and technological applications of science.