Teaching Forces – Misconceptions and how to overcome them

Forces and how to teach them 

A great Newton’s third law experiment to try below – more ideas on my Forces Pinterest page here 

science-playground

One of the many problems faced by physics teachers is that the terminology we use in a very precise way is often used very arbitrarily in the ‘real world’

May the Force - sorry !

May the Force – sorry !

Forces is a bad one;

  • “She forced me to do it”
  • “It was an act of force”
  • A force of nature
  • The armed forces  
  • Possibly the worst of the lot when it comes to confusing the concepts  –“May the Force be with you “ !

The Force?  something we can carry around with us?

Before we start teaching Forces we should look at the common misconceptions  

Probably the biggest single misconception is that when you push or throw an object that there continues to be a force in the direction of motion.  It’s natural and common sense to assume that a driving force is needed to keep an object moving at a steady speed because that is our everyday experience.

When you stop pedalling on a bike you come to  stop. Therefore you must need a force to maintain a constant speed – dont you ? . We live in a world with friction, but as we cant see it often it isnt accounted for.

Carol Davenport @DrDav has written a blog for making the invisible visible, its  for Ks2 but it gives a good overview of what our students should know ( but probably dont !) here

Teach momentum first?

Another issue is that we usually  haven’t taught momentum yet. Should we do that before we teach forces?

I dont do an in depth  quantitative analysis of momentum.  I usually just  ask the question ‘Which would hurt you most if it hit you a beetle or a train?

Students usually respond-  a train, then you point out what would happen if the train was moving really slowly and the beetle really fast? (I once had a Rhinocerous Beetle bounce off my forehead when cycling down a hill – it hurt !!)

So there are 2 properties we need to consider , the mass and how fast it is moving – its velocity. Multiply these two things together and we have momentum.  Momentum is useful for scientists when studying collisions or how difficult it is to stop a moving object.

It is an interesting point to consider as to whether momentum is a more useful property than simply velocity when setting speed limits. Although the debate I had with a police officer who pulled me over on my motorbike for travelling the same velocity as the 4×4 in front of me that had 10 times my mass, was short lived and fruitless.

Videos – Lots of collision videos are around. Im wary of using many of the car crash ones as they may involve fatalities. Get your students to find them 

Bubble soccer – The ultimate momentum experiments?

Stop a train?

Another problem with teaching physics is that students come into our classroom  with a set of belief systems. They think they understand forces and they have models in their heads which sadly are usually wrong.  This research indicates merely telling people the right things may not be effective at all 

In this blog we look at the role of confusion here

So what actually is a Force? 

Its a question few people can accurately answer

Identifying, measuring and representing forces – Misconceptions we may need to deal with 

Pupils often think that:

  • only animate objects can exert a force – thus, if an object is at rest on a table, there are no forces acting on it
  • a rigid solid cannot be compressed or stretched
  • all forces need objects to be in contact to have an effect
  • friction only occurs between solid objects
  • things fall naturally – no forces are involved; barriers stop things falling
  • gravity stops acting when the object hits the ground
  • there is ‘more gravity the higher up you go’ because things dropped from higher up suffer greater damage when they hit the floor
  • mass and weight mean the same thing and they are equal at all times
  • mass and volume mean the same thing
  • gravity only affects heavy things
  • gravity only works one way – the Earth attracts the Moon but the Moon does not attract the Earth
  • Earth’s magnetism and/or spin create gravity
  • astronauts are weightless in an orbiting spacecraft because there is no gravity
  • magnetic field lines are really there – a magnetic field really is a pattern of lines
  • all metals are attracted to a magnet
  • all magnets are made of iron
  • magnetic poles are always at the end of the magnet
  • larger magnets are stronger than smaller magnets
  • all materials that can be magnetised are magnets
  • objects float in water because they’re ‘lighter’ than water or sink because they are heavier; wood always floats and metal always sinks
  • all floating objects float because they have air in them
  • all objects containing air float
  • there is no/less gravity in water
  • power, work, energy and force all mean the same thing.
Forces Simulations – Interlude from reading  you might find some of these useful  
Nice ideas from eChalk here
PhET – here 
Forces and motion – Misconceptions 
Pupils often think that:
  •  if an object is moving there must be a force acting on it
  • if an object is stationary there are no forces acting on it
  • if a force acts on an object it will inevitably move
  • force is a property of an object; an object has force and, when the force ‘runs out’, it stops moving
  • acceleration can only occur in the same direction as an object is moving
  • when dropped in a vacuum, heavier objects will reach the ground first
  • falling objects stay at the same speed as they fall
  • opening a parachute during freefall makes the skydiver go upwards
  • rocket propulsion is due to exhaust gases pushing on something behind the rocket.
  • Pupils often confuse speed, acceleration and velocity; distance–time and speed–time graphs.

What they already know

One of my favourite activities is to use a plastic crossbow – you can buy them here

Toy crossbow

put a 1N apple on my head wear safety goggles and ask for a volunteer to shoot the apple off my head on the count of three.

On the count of 2 I stop and ask the class Should they aim straight at the apple, above it or below it?  Virtually every student says above Why?  get them to think for a bit What about if I move further away? They all know you have to aim even higher. So what do you know?  That forces, in this case gravity, change the motion of a body and the longer the force acts for, the greater the change in motion

We can do an analysis on the crossbow bolt to really assess our students understanding of Forces

crossbow powerpoint

The reason for using an apple that weighs 100g is that we can reinforce that it weighs 1 Newton. Then we can ‘show’ a Joule – Throw the apple 1 metre in the air and you have done 1 Joule of work (Work (J) = Force (N) x Distance (m) travelled in the direction of the force) So if we consider a chemical store of energy – such as a packet of biscuits . How many Joules would there be stored in a packet of biscuits ? Get your students to guess – biscuits given to the 3 closest ? They massively underestimate as the answer is often over 2000,000 Joules. So I eat a packet of biscuits and I can throw an apple in the air two million times ! or fire one two thousand kilometres high ! Link to this to power stations and why coal and oil are used as fuels. In reality we cant do this , why not? Relate answers to the ideas that we are massively inefficient at transferring energy – You can burn poo as a fuel source ! We can go cross- curricular with biology and look at that we are homiotherms and hence transfer around 75 Watts of thermal energy . Poikilotherms such as snakes and crocodiles dont need anything like as much food as they dont need to regulate their internal temperature. Cue some gross videos of massive snakes and crocodiles eating things

Analysing graphs 

I find many students struggle to analyse graphs and to see the point. I want them to see that graphs tell stories – See below for one of the ideas I use 

Falling objects 

It is counter intuitive that a feather and a bowling ball would fall at the same rate if there was no drag . Here is Brian Cox

or the Hammer and Feather on the moon – Or discuss  conspiracy theories  here 

Terminal Velocity 

A man and a cat fall out of a plane at the same time. Sketch on the same Velocity – Time graph their motion . Get students to think about what information do they need –  This may help 

Answer below

To be updated

The ubiquitous skydiver

http://www.cyberphysics.co.uk/topics/forces/terminal_velocity.htm

Forces and turning effects – This is for a future blog . How would you deal with these common misconceptions 
Pupils often think that:
  • only equal masses can be balanced on a seesaw
    the pivot has to be between the two forces that are acting
  • forces only cause changes in speed, not direction
  • when a force makes an object travel on a circular path the object must get faster, i.e. the force must cause a change in speed, not just direction
  • cornering objects are forced outwards by a force called centrifugal force.

Forces and pressure – misconceptions and ways of teaching

Pupils often think that:

  • pressure and force are synonymous
  • pressure in liquids and gases can be stronger in one direction than another
  • pressure arises from moving liquids or gases; still gas or liquid cannot exert a pressure
  • moving fluids cause higher pressures
  • liquids rise in a drinking straw because of ‘suction’
  • fluid pressure only acts downward.

 

The misconceptions are taken from there

Transforming Technology with a Single Device for Free – Plickers

Many schools still have a no mobile phone policy for students or lack 1:1 devices, but there are a few things that can be used if the teacher has a or phone/tablet. One of the simplest of these is Plickers which is a way of collating multiple choice responses from students. Its free and brilliant

  1. Students are given a unique barcode ( a paper plicker )
  2. The teacher asks a multiple choice question (these can be set up beforehand or used on the fly)
  3. The students show their answer by holding up their paper plicker – the orientation of the plicker allows them to choose ABCD
  4. The teacher scans the class with their phone
  5. A bar chart of responses is immediately produced on the phone and if you have wifi/3G on a linked computer as well – It will work on your phone without any signal so dodgy wifi is not a problem
  6. Reports of responses are stored on the plickers website so progress (or not ) can be demonstrated

More detail

The teacher prints out plicker cards which have a number on them and 4 letters. They act like a QR code in that when they are held up and scanned with the camera on the phone/tablet the number of the card is recorded  as well as the response of that card A to D depending on the orient

plicker-codeation of the card when the student holds it up. The letters are written small so that the other students cant see what each person is choosing. Often with mini whiteboards students will look at others responses before making theirs. You can get your students to write the letters on the back of their cards if they have any disability or for younger students

The teacher then scans the class

0c8c3b21.PlickersSplash2

It records multiple cards at once and a rescan will not mess up your results as it only records the individual cards once. You can set the orientation of your phone but dont change it . Without thinking I rotated my phone from portrait to landscape and wondered why everyone thought the answer was C when it was A

plickers pic

Results are shown on your device and if you have wifi on the website as well

plickers bar

On the plickers website classes can be set up and the cards assigned to students. The student then sticks the card in their book/planner  so that at any time we have an instant way of assessing what the class is thinking. Reports are saved on the website so  progress (if any is made) can be demonstrated.

Plickers_report plick report

A video overview

A nice slideshare tutorial is here

  • Plickers in PE here  PE teachers might want to laminate cards to take out with them

 

 

 

 

Three Act Science – Alternative approaches to Science Teaching

Three act science is based on the work of Dan Meyer see his TED Talk here  who created three act maths in order to get students to think about and engage in maths – rather than simply follow sets of processes in order to get the ‘right’ answer.

Dan felt that his students had the following issues

Meyer students lack

 

Any science teacher will recognise these as the same problems we face. Students wait for us to help them and give up if we don’t,  We think they’ve nailed it at the end of the lesson only to find that at the start of the next lesson they are mystified when you mention the concept again. If an exam  question is worded slightly differently to the ones they have practiced they are completely flummoxed. They ask us to prepare them for exactly what will come up in the exam and blame us if it doesn’t.

Professor Guy Claxton in his latest book Educating Ruby   has the idea of seven Cs that give us a good starting point on what we want to our students to be enterprising, friendly, moral and imaginitive. These are :

Curious – Have a natural interest

Collaborative – Be able to be part of a team

Communicators – Effectively put their point across

Creative – Produce new and interesting ideas and material

Committed – Not need any external drivers or rewards

Confident – Be prepared to present and defend opinions

Craftmanship – Pride in their work and being the best that they can be

Three act science aims to help develop these skills  not just exam decoding. Irrespective of your teaching style – be it traditional or progressive these ideas add value to learning. It also fits in perfectly to strategies such as the South Australian Learning to Learn  which I feel hits all the things I’d want an education system to be

The principles of three act science are:

Act 1: the hook

This is a demonstration or video that is either counter intuitive or creates curiosity. The aim is to get the students engaged in deep thinking either in order to explain what they think will happen or why it happened.

An example is this one. What order will the cartons fall over in?

To take this a stage further we can ask students to make a prediction – The work of Professor Mazur implies this is essential.  We also should  create a degree of confusion  – see another blog I wrote  here  or the original here 

An effective way of assessing learning and ideas is to ask students to put their left right or both hands up to indicate their choice. So for example for the cartons above. If you think the last carton to fall over is the full one on your left, raise your left hand. If you think its the half full in the middle raise both hands. If its the empty one on your right raise your right hand. Now keep your hand/s up , go and find someone who disagrees with you and tell them why they are wrong.

We now go and listen to the ideas and misconceptions and articulate them to the class. What we are trying to do here is to use visible thinking  . The simple premise being that if we want our students to think like scientists we need to model that thinking for them. We are also drawing attention to misconceptions and getting students to think about them. The effectiveness of this strategy is outlined in the Dr Derek Muller aka Veritasium in his doctorate research – Full research papers here

Another strategy to add thinking at this point is  WMHI?  This is simply asking the question What Might Happen If …. ?  and get the students to continue – the boxes were lighter/heavier , sand was used instead of water ….  then they can work it out or try it out.

Act 2: The explore

So we have started an engaging activity, now is the time to explore and develop problem solving skills. What do we need to know in order to find out. What information have I got?  How might this link to other things I have learned or seen before?  (You could link this to SOLO taxonomy  here though David Didau has some advice on using it more for planning than the students here ) What value if any do the other student ideas have ? Could my initial beliefs be wrong? (surely not – confirmation bias is very powerful!)

We can also take it a step further – So for the cartons  if they all think the half full is the most stable – at what stage does reducing the amount of fluid from half full make it become less stable ie what is the point of maximum stability ?

Act 3: The reveal

We might want to use the Zeigarnik effect – basically  we lose interest in the cartons when we know what the answer is. We continue to think about incomplete activities so dont rush to do the reveal.

Want to know the answer to the cartons? Try it yourself = or look for the clue in the first video

There will be a whole series of three act science activities launched on a new youtube channel threeactscience and coolscistuff – So please watch this space

Please contribute any ideas or thoughts in the comments section

 

 

 

Put the Glory back into your classroom – Humanising the education system

As a scientist I am a great believer in research. There is some fantastic and informative research around but I have one great worry. As we strive towards efficiency I think we may be losing something possibly more important – The Glory of the Ride

Zen Dog

Are you the teacher you wanted to be? The one who took the students on amazing journeys and instilled lifelong learning and a passion for your subject?

Or have you been turned into a destination focussed, pass the exams, bogged down in a curriculum parody of your ideal?

Efficiency can come at a cost. I went to swimming race training as a child. We pounded up and down, used deliberate practice. It was hard, but efficient.

It has been very useful to me . I’m a beach lifeguard, kayak instructor and as a surfer it may even have saved my life.

So whats the problem?

Well I never swim for pleasure – purely a purpose. Would never dream of swimming for no reason

I worry that our students will never consider learning to be a pleasure, simply something you do fora purpose.

So how can we put the glory back into your classroom?

Watch this space for the follow up blog

Motivating the Lower achievers – Humanising the Education system – Ipsative Assessment

Think about something that you have little talent for. Now imagine that you spend your days continually assessed on that area that you lack talent in.  You are constantly compared to your peers and shown how poor you are.

I love singing, but sadly have very little talent, not helped by congenital hearing loss. I wasn’t aware of my lack of ability, choosing to ignore the negative comments until I used the playstation game Singstar that brutally and quantitatively confirmed how bad I was.  Did this motivate me to try harder ?  It did briefly , although it was more about trying to find a song I could sing (Clash Should I stay or should I go! ) but being trashed by everyone soon lost its appeal and now I don’t sing any more in public. Which is no great loss to the world, but it is to me.

The thought that singing ability could be what the education system values allows me to empathise with the lower achievers. Of spending my days singing in front of others and however hard I try most other people are better than me. I may have other talents (I may be deluded here) but these are not recognised. My only value is my singing, the good singers are celebrated and their superiority over me quantified and celebrated.. This carries on for 11 years until in relief I leave an education system that has utterly failed and humiliated me.

This is how many lower achievers spend their school life. You are really not very good and if you put lots of effort in you probably still wont be . You can argue for a growth mindset at this point (which I believe in to a point)   or take the view that we are telling penguins that they might be able to fly if they flap their wings really hard (reality also has a place )

Research from the EPPI in 2002 has found that Summative assessment, so loved by those who are good at it and who also run the system  can be highly motivating to some higher achievers , but damaging to many others with the lower achievers particularly vulnerable.

The current widespread use of summative assessment and tests is supported by a range of arguments. The points made include that not only do tests indicate standards to be aimed for and enable these standards to be monitored, but that they also raise standards. Proponents claim that tests cause students, as well as teachers and schools, to put more effort into their work on account of the rewards and penalties that can be applied on the basis of the results of tests. In opposition to these arguments is the claim that increase in scores is mainly the consequence of familiarization with the tests and of teaching directed specifically towards answering the questions, rather than developing the skills and knowledge intended in the curriculum. It is argued that tests motivate only some students and increase the gap between higher and lower achieving students; moreover, tests motivate even the highest achieving students towards performance goals rather than to learning goals, as required for continuing learning.

What were the findings ?

Evidence of impact – Remember this was from 2002

Between them, the identified studies considered a number of the component aspects of motivation, but none considered all. The following main findings emerged from studies providing high-weight evidence:

• After the introduction of the National Curriculum Tests in England, lowachieving pupils had lower self-esteem than higher-achieving pupils,whilst beforehand there was no correlation between self-esteem and achievement.

• When passing tests is high stakes, teachers adopt a teaching style which emphasises transmission teaching of knowledge, thereby favouring those students who prefer to learn in this way and disadvantaging and lowering the self-esteem of those who prefer more active and creative learning experiences.

• Repeated practice tests reinforce the low self-image of the lower achieving students.

• Tests can influence teachers’ classroom assessment which may be interpreted by students as purely summative, regardless of the teacher’s intentions, possibly as a result of teachers’ over-concern with performance rather than process.

• Students are aware of a performance ethos in the classroom and that the tests give only a narrow view of what they can do.

• Students dislike high-stakes tests, show high levels of test anxiety (particularly girls) and prefer other forms of assessment.

• Teachers have a key role in supporting students to put effort into their learning activities.

• Feedback on assessments has an important role in determining further learning. Students are influenced by feedback from earlier performance on similar tasks in relation to the effort they invest in further tasks.

• Teacher feedback that is ego-involving rather than task-involving can influence the effort students put into further learning and their orientation towards performance rather than learning goals.

• High-stakes assessment can create a classroom climate in which transmission teaching and highly structured activities predominate and which favour only those students with certain learning dispositions.

• High-stakes tests can become the rationale for all that is done in classrooms, permeating teacher-initiated assessment interactions.

• Goal orientations are linked to effort and self-efficacy.

• Teacher collegiality is important in creating an assessment ethos that supports students’ feelings of self-efficacy and effort.

• An education system that puts great emphasis on evaluation produces students with strong extrinsic orientation towards grades and social status.

It would appear that the more importance we put on summative assessment the more likely our education system is to become;

  • A narrow, what gets tested gets taught, system
  • Focussed on performance rather than learning with all the damage that this entails
  • A qualification system rather than an education system
  • Highly divisive with those exam decoders motivated by success and those without this arguably arbitrary skill
  • One that only values those high performers and there is evidence these high achievers at school do not continue into society as high achievers in life  (link to blog)
  • One that dismally fails and alienates many students who leave feeling they have no value and have had their school years wasted

Does these sound depressingly familiar?

Formative assessment (see blog here for ideas ) has developed hugely where students are told what they need to do to improve, however this for some has only limited value. Would I be motivated to sing in public if after tuition I went from being appalling to pretty awful? Probably not. The system has inherently damaged many of these students and caused them to withdraw from putting in effort. You can only be humiliated if you have appeared to have tried. Want to keep your self esteem? Then don’t participate, show you don’t care or deliberately under perform to demonstrate your contempt for the system.

It doesn’t matter how good your formative assessment is if your students cant see the point in improving and are still measured against their peers.

Enter Ipstative Assessment

Rather than comparing yourself to the world, you look at creating personal bests. I am a cyclist and if I compared myself to Chris Hoy or Bradley Wiggins I could never feel good about myself. I am however motivated to improve my best times and that has sufficient value to not care how far behind the others I a would be.

This is the fundamental principle behind appositive testing. Research has been limited to distance learners but the results encouraging here http://eprints.ioe.ac.uk/6744/1/Hughes2011Towards353.pdf  and workshop files here 

You mark progress rather than simply products. Bringing in formative assessment in order to improve their appositive mark.

To give a measured grade a students work is compared to a previous piece of work

If a student has improved from 50% to 60% they would get an ipsative mark of 10%

The focus is on improvement and being the best that you can be hence everyone can make progress

The research which was the effects on distance learners looks highly encouraging and it makes sense as a human being.

I can find limited evidence of it being used in classrooms so please get in touch if it has been trialled and any thoughts on it

Advice on watching the eclipse for students and schools

26th_oped_TimeZone_1218919e

Eclipses are a relatively rare event and are fantastic learning opportunities  – a timetable is available here  for the next ones . The one on March 20th follows this path

path720

A really useful booklet can be downloaded from the Royal Astronomical Society here (Thanks to Alistair Gittner)

Safety is of paramount importance so please ensure that students are given this advice

Viewing a solar eclipse is potentially hazardous and should only be attempted with caution. You should never, ever – under any circumstances – look directly at the Sun!  – Even when it is partially covered and might not look very bright

Sunglasses will NOT protect your eyes from potential permanent damage from looking at the Sun.

Even worse is looking directly at the sun through binoculars or a telescope, though these can be used safely to project an image onto a card.

Safe ways are outlined below from NASA

sun-eclipse-viewing-120509b-02

Eclipse glasses can be bought ( in bulk ) from here   but quickly to guarantee delivery in time

A box pinhole projector can be very effective – although you may look a little strange ! Instructions are here  A photo or video could be taken by a phone from inside the box

pinholeprojection

 

Want to photograph the eclipse ?

There is a very useful article here   Dont destroy your cameras sensor – Use an appropriate filter !

Want to use your mobile phone? It will probably be a waste of time as you will see only a tiny blob. You can take a photograph from the objective of a telescope , but the telescope should be filtered to prevent damage to the cameras sensor . The photo below was taken by  Dean Regas  here

solar

There are some useful resources with videos on how to build pinhole cameras etc  here

Shoe Box Pinhole camera

I like this Pringle Can viewer here

can_up_down

Please add any more useful sites /videos and tips in the comment section

 

 

 

 

Confusion vs Clarity – Great teachers who beat themselves up and poor ones who think they are great

We like clarity – defined as clearness or lucidity as to perception or understanding; freedom from indistinctness or ambiguity. So surely this is what we as educators should be aiming for. Brief succinct and to the point and our students are happy.

Confusion on the other hand is something unpleasant and to be avoided says conventional wisdom.  This may be true for superficial tasks such as rote memorising, but there is mounting evidence that confusion promotes learning at a deeper level of comprehension.

Science is different than most subjects in that most students enter our classrooms with a preconceived notion of scientific concepts . Their minds are not a blank slate (sadly as that would be easier) but a mass of beliefs, many of which are wrong.

If we use the classic teaching idea of showing a demonstration and then having a discussion about what they have seen, that must be effective. 

demo-observe-discuss

It would appear not, from research from Eric Mazur,the Harvard physics education researcher that we are better off not doing the demonstration at all unless you get them to predict an outcome first. If only the demo is viewed you tend to remember it in a way that confirms your belief rather than the reality. This is a common fallacy that we remember things as they really are. Making the prediction seems to force us to realise that we got it wrong and hence more likely to change our minds. The social discussion afterward seems to have no direct effect on their performance although longer term benefits were not evaluated. Nor was peer instruction used which would have been interesting.

Dr Derek Muller – with the youtube channel Veritasium exploits this improved performance with his videos that deliberately confuse  Great Youtube Channel

Students prefer not to be confused and far prefer teachers who give clear explanations,  .  Is this always a good thing?  Mazur tried an on-line test on several topics, where he asked students a couple of hard questions (novel situations, things they hadn’t faced previously), and then a meta-question, “Did you know what you were doing on those questions?”  Mazur and his colleagues then coded that last question for “confusion” or “no confusion,” and compared that to performance on the first two problems.

confusion-learning

Again the results are counter intuitive. The confused students actually perform way better than the ones who are not. Which probably means that the students who are happiest with their teachers are the poorer performers – (this has huge ramifications for fee paying schools who want their teachers to be popular )

For teachers we may be faced with the choice of being popular and ineffective, or unpopular and effective!

Not only are students poor at judging how effective their teachers are they also according to Mazur are very poor at predicting their own performance.

This could be partly down to the Dunning-Kruger effect where people have a tendency to overrate their own ability. This is usually down to ignorance rather than arrogance. In virtually every survey done more than 50% of people judge themselves as being better than average attractiveness, intelligence and ability as a driver. Perversely the least competent are the ones most likely to overrate themselves and the highest performers underrate themselves.

S_psp7761121fig2a

Perceived logical reasoning ability and test performance as a function of actual test performance

An article here outlines Dunning – Kruger effect and there’s a detailed blog here 

Add all these things together and you can have very popular poor performing teachers who think they are great as they lack the analytical skills to see their failings and unpopular, but  high performing teachers who beat themselves up. It can be a cruel, unfair  world!

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I will be launching a new YouTube Channel to support this so please watch this space