Language and understanding in Physics

Acknowledgements:Brian McKittrick, Kim FalloonHelen McDonald & Geoff Davies

Force

• Forces are pushes and pulls• Forces cause objects to speed up, slow down, change direction,

remain stationary and change shape• Many forces can act on an object simultaneously• Forces acting on an object can be added together – the net

force as a mathematical quantity, not a physical quantity• The net force is identical in size to the product mass of object

and acceleration of object • The net force acting on an object = , that is forces are

associated with momentum and kinetic energy changes, which when combined with conservation rules lead to transfers and transformations of these commodities

• In contemporary physics force is not a significant parameter, but rather an outcome of statistical averaging of field interactions.

• Force as a word used to describe the transfer of particles associated with a field

A: 1 kg

B: 2 kg

C: 3 kg

earth

Forces and objects How many vertical forces act on objects A, B and C respectively?

table

On A On B On C

By A _ 10 N down

0 N

By B 10 N up

_ 30 N down

By C 0 N 30 N up

_

Forces and objects

• Object B moving to the right at a constant speed is pulled to the right by a horizontal force

• Object B accelerates to the right is pulled to the right by a horizontal force

mass

• Mass is a measure of the amount of “stuff” a body is made of

• Mass describes the amount of inertia an object has and hence the kinematic response an object has to a net force

• Mass describes the strength of a gravitational field around an object

• Mass describes the energy content of an object• Why does inertial mass yield the same numerical value as

gravitational mass?• What might happen if there were mass with a negative

signature and that momentum p = • Maybe equal amounts being created at the start of this

current universe? Is space/time the real antimatter?

weight

• The weight of an object is the force of gravity acting on it

• Does an apple weigh as much as the earth?• What is meant by apparent weight?

Electricity – charge and motion

• The mean speed of a free electrons in thermal equilibrium is given by . In a room temperature conductor free electrons have a mean speed of 1.1 × 105 m s-1. The drift velocity of an typical electric current is of order 10-2

m s-1; this differs by a factor of 107. How do we talk of an electric current in this light?

• The mean speed due to thermal motion results in electrons having a mean kinetic energy of 0.03 eV at room temperature.

• Potential difference – the energy gained or lost per coulomb of charge – an open ended discussion about

• Does charge have to pass through a cell to gain potential energy?

• General circuit theorems – conservation of charge leading to current conservation at a node, conservation of energy transfer leading sum of potential around a closed loop equalling zero.

Fields

• What is a field and how is it used in secondary school physics?

• http://en.wikipedia.org/wiki/Classical_field_theory

• What are examples of fields? In what sense are they real?

• Can a field store potential energy? How does this description stand with the language used to describe lifting a mass in a gravitational field?

light

• What language do we use when describing diffraction and interference?

• How do we deal with the particle model for light – the photon – for some interactions and retain a wave model of light for propagation?

• How do we resolve G. I. Taylor’s experiment circa 1900’s?• Is there a consistent language for use in modern physics?• What would a candle look like to a group of observers if it

emitted electromagnetic radiation at a rate of 1 photon per second?

inside the nucleus

• What is the nucleus composed of? • Is it reasonable to think of the nucleus as being composed

in individual protons and neutrons? Both the proton and the neutron are modelled as being composed of 3 quarks.

• A free neutron has a half-life against beta decay of about 10 minutes.

energy, kinetic and potential

momentum

An unbalanced force acting on an object over a displacement gives rise to a change in the kinetic energy of the object.

A net force acting on an object over a period of time gives rise to a change in the momentum of the object.

What is the difference in the meaning of the words “unbalanced” and “net”?

energy, kinetic and potential

An unbalanced force acting on an object over a displacement gives rise to a change in the kinetic energy of the object.

Student explanations and descriptions

• The momentum of the car caused the brick wall to break

• The passenger flew through the windscreen because of the accident

• When the starters gun went off, I pushed myself forward• The force of the moving ball propelled it through the air• The cell supplied energy to the charge as it passed

through the cell• I can see my feet standing in front of the mirror• The electricity moved around the circuit at the speed of

light

task instruction

Term  

Definition Typical learning examples

Analyse Identify components, elements, constituent parts of the whole and identify the relationships between them

Consider presented information and clarify concepts and knowledge; use qualitative and quantitative methods to distinguish between components (words, tables, labelled diagrams, calculations, graphs); recognise patterns; identify and relate implications; graphical analysis 

Apply 

Use knowledge (ideas, formulae, principles, theories, laws, models, techniques) in a new situation or context 

Propose a solution or response to a problem or issue; show steps; use algebraic and/or graphical methods as appropriate 

Calculate 

Use mathematical formulae and modelling to solve quantitative problems 

Solve numerical problems by using formulae and mathematical processes; find the numerical value of an unknown variable or constant 

Compare 

Identify the similarities and differences between two or more objects or processes

List, tabulate or use a graphic organizer to identifysimilarities and differences

Describe 

Communicate the characteristics and features of an event, object, procedure or process

Use written or visual representations to communicatecharacteristics or features

Design 

Create a plan, object, model, system, simulation or set of procedures to suit a particular purpose ;

Combine knowledge, skills, materials and processesto develop a solution to a problem

Determine 

Find out, based on reasoning, observations and information

Recognise a quantity (often without the use ofcalculations); interpolate; extrapolate; estimate

Evaluate 

Make reasoned judgments or decisions on given or collected information, based on established criteria

Assess the merit (strengths and limitations) of ideas, processes or procedures and reach a conclusion; validate evidence; choose from options based on reasoned arguments 

Explain 

Make clear; account for the reason for something or the relationship between cause and effect; state why and/or how 

Provide reasons mechanisms and outcomes, incorporate quantitative data as appropriate 

Identify 

Recognise particular elements of a whole or part; select from a number of possibilities; select relevant information or aspects of key ideas

Recognise and name/label a specific object, element, component or underlying principle or concept; label/annotate components of a system, model or diagram 

Interpret 

Take a form of information and make conceptual meaning from it 

Derive meaning from information presented in multimodal texts (for example, written, aural and diagrammatic), tables, images and graphical formats 

Model Reproduce conceptual understandings and principles; physical structures and systems

Construct a visual, physical, algebraic or graphicalrepresentation of concepts, principles or processes 

References

• Physics questions without numbers, Dick Gunstone and Richard White, Faculty of Education, Monash University, 2012

• Physics 1 and 2, Halliday and Resnick, Wiley 1966• http://en.wikipedia.org/wiki/Classical_field_theory