Force Arrows
Forces and Motion

Finding forces - Teaching approaces

Classroom Activity for 5-11

A Teaching Approach is both a source of advice and an activity that respects both the physics narrative and the teaching and learning issues for a topic.

The following set of resources is not an exhaustive selection, rather it seeks to exemplify. In general there are already many activities available online; you'll want to select from these wisely, and to assemble and evolve your own repertoire that is matched to the needs of your class and the equipment/resources to hand. We hope that the collection here will enable you to think about your own selection process, considering both the physics narrative and the topic-specific teaching and learning issues.

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Selecting and developing activities for finding forces

Force Arrows
Forces and Motion

Selecting and developing activities for finding forces

Classroom Activity for 5-11

Things to think about when selecting and developing activities to aid the teaching of 'finding forces' based on the Physics Narrative and the Teaching Guidance.

Ideas to emphasise here

  • Connect interactions between objects with the idea of a force
  • Adopt consistent conventions about where and how the arrows are drawn
  • Relate floating and sinking to forces, not to rules about displaced fluids
  • Relate 'friction' to the mechanisms of friction
  • Focus on the physical reasons for placing arrows
  • Giving real experiences of forces acting at a distance
  • Exploiting the tangible effects of magnets in regions of space around the magnet
  • Relate electric, magnetic and gravity forces, without conflating them
  • Separate the mass of an object from the force of gravity acting on the object, without being dogmatic

Teacher Tip: Work through the Physics Narratives to find these lines of thinking worked out and then look in the Classroom Activities for some examples of activities.

Strategies for supporting learning

  • Draw on learners' conceptions of their own actions and relate these to force
  • Explore and expose children's ideas of forces
  • Draw out children's everyday ideas about motion and the forces required
  • Introduce children to a new way of seeing – with forces
  • Convince children that inanimate things can push, just like they can
  • Develop the idea that a mechanism underpins the interaction that is replaced by force
  • Convince children that air can exert forces
  • Draw on children's own experience of action at the distance, probably through experiences with magnets
  • Draw on children's experiences, some of which will be vicarious, to establish the reality of gravity in space
  • Explore something of the mystery of action at a distance

Teacher Tip: These are all related to findings about children's ideas from research. The teaching activities will provide some suggestions. So will colleagues, near and far.

Avoid these

  • Drawing arrows next two objects, or near objects, when you intend the force be acting on the object
  • Don't act as if the placing of arrows is obvious and open to a simple inspection
  • Don't refer to forces cancelling out
  • Avoid using complex objects on which forces might be acting (with internally moving parts – bicycles, cars, people.)
  • Using friction as a blanket term, without reference to its physical origins
  • Treating contact forces exerted by inanimate objects as obvious
  • Stating, without sharing the appropriate experiences that give the statements meaning
  • Treating action at a distance as obviously acceptable
  • Acting as if the similarities between the three non-contact forces always have been obvious
  • Over-emphasising the similarities
  • Conflating the terminology and representations for the three different forces

Teacher Tip: These difficulties are distilled from: the research findings; the practice of well-connected teachers with expertise; issues intrinsic to representing the physics well.

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A sequence to develop ideas about friction: grip, slip, drag

Friction
Forces and Motion

A sequence to develop ideas about friction: grip, slip, drag

Classroom Activity for 5-11

Frictional forces are a group of forces that affect movement. They can set things moving (as when you expect your shoe to grip the floor: think about when it does not – icy patches wreak havoc with our expectations of getting going) and these are grip forces. Another set of frictional forces are slip forces: these slow things down as one surface moves past another surface (and both are the surfaces of solids, not fluids). This activity is an exploration of these two kinds of grip forces, to encourage children to think through the detailed mechanisms that underpin these forces and therefore to be able to reason about changes that well increase or decrease the grip or slip force. One reason for focusing on mechanism is that it provides a field guide to help children identify where to expect forces. Another is that this particular focus enables a physical richness to the explanations that afford exploration, rather than simply associating the label friction with the phenomenon that you're looking at.

Forces are best represented with labelled arrows, of different lengths to show different values, and we'd suggest that you make extensive use of these as physical labels on things, as this makes it clear that forces are acting on objects, with some effect on the motion of the object. That's where all this discussion about forces is heading in the the long term.

There is a third member of the frictional group of forces, that is not dealt with here: drag. Drag is the force exerted by a fluid (a liquid or a gas) as the object moves through the fluid, and you may well meet particular examples described as air resistance or water resistance. The mechanisms underpinning these interactions are complicated – even more complicated than grip and slip. And even more so if it's something like a boat that moves at the interface between two fluids (water and air). So here we'd suggest being very clear in your own mind that you're only dealing with frictional forces between solids.

Meeting reality: valuable experiences

  • Trying to lift slippery objects
  • Starting and stopping moving on more or less slippery surfaces

A sequence for developing the idea

The idea of friction is often rather vague, and used as a word to avoid explaining, rather than to thinking in some detail about the mechanisms at work. This sequence encourages you to be much more explicit, so allowing children access to a much richer understanding. Such detailed and careful thinking and representing provides them with a starting point for asking much more interesting and much more fruitful questions.

Teacher Tip: The ideas are developed in the Physics Narrative.

Practice labelling things isolated from their environment, with forces to represent interactions with the environment, using cardboard arrows.

Discussion about instances


Explore children's starting ideas about forces by discussing everyday situations.

Cardboard arrows


Helping children to identify forces and give them a language to describe forces. Exploring pupil's ideas – and making them explicit – is a central feature of this introductory work.

Looking through forces spectacles


Set an everyday task that depends on frictional forces – for example lifting a tin.

Lifting a tin


Introduce the grip and slip force arrows with a pair scrubbing brushes. Relate surface roughness to the ordering of the grip and slip arrows.

Visualising what happens at surfaces for grip and slip


Pull on the slippy and grippy puppets pressed on everyday surfaces.

Ordering slip or grip forces


Describe the experiences of the pull by labelling with slip or grip force arrows of different lengths.

Everyday grip and slip


Pulling with a standard force

Getting a feeling for a one newton force


Stop something moving over with grippy and slippy puppets.

Braking uses slip forces


Messages from research and practice: specific tripwires for this idea

Children have plenty of experience of pushing and pulling things to change their location. But they have rather fewer experiences of acting to change the motion of things, because frictional forces are so pervasive. Give something a shove, and it might move a bit, but it will then very likely come to a halt: the location has been changed, but the motion has not been (except in the short term). There are two significant challenges here. The first is that once you've analysed the world carefully enough, force changes motion, and not location. The second is that children need to generalise their idea of agency, so that they can imagine the world as a place where many different things in the environment can exert forces, and not just human pushes and pulls.

Prior ideas to re-activate and build on

  • Forces are represented by arrows
  • Forces are like children's pushes and pulls

A key element of making ideas about frictional forces worth teaching is to go well beyond labelling something as to do with friction: drilling down into the physical mechanisms, imagining the interactions between the thing and its environment that provide these frictional forces. It's a good plan to expect to work towards some detailed descriptions of how things are, through sketches, words and physical experiences, rather than stopping as soon as the word friction is reached.

Teacher: Well, here we have a stone sliding across ice. It stops after a while…

Abi: I know, it's friction, miss.

Teacher: Yes, but what's rubbing against what: where do we need to put the arrow?

Dave: The bottom of the stone's rubbing on the ice.

Teacher: And the arrow?

Alex: It's a slip arrow, the slip force.

Teacher: A long arrow, for a big force?

Abi: No, no, no. It's a short one.

Geoff: Because the ice is smooth.

Abi: So it's only a small slip force, and the stone takes a long time to stop.

In many cases the explicit link to the reason for expecting there to be a frictional force there at all, and the resultant effect on motion, are best drawn out, so that any difficulties can be made explicit.

The challenges and difficulties are explored in the Teaching and Learning Issues strand – here is an essential selection:

Forces are a part of the imagined world of the physicist and so you cannot see them, however powerful the telescope or microscope. You do have to re-describe the lived-in world in a new and rather special way.

I can't see a force – so it isn't there


The conflation of force and motion is well documented in the research. There are good reasons to believe children have experiences in the lived-in world that reinforce these kinds of confusions.

Force equals motion: no motion equals no force


Force equals motion: motion equals force


Air seems very thin, and so it seems more or less unbelievable that it could exert a significant force on moving objects.

Air resistance – how can it work?


Teacher Tip: Avoid arguing from the effect to the implied cause, so don't use: The stone takes a long time to slow down, so the slip force must have been small.

Teacher Tip: These challenges and some suggestions for working with them are more fully explained in the Teaching and Learning Issues.

Representing and reasoning: doing physics

Re-describing the world in terms of forces acting on objects needs imagination. Since forces cannot be seen, even with the most powerful microscope or telescope, and are not obviously just there, it is worth emphasising this imaginative aspect. Thoughtful and precise drawing of diagrams representing different forces using arrows is, at the same time, both fruitful and requiring significant work.

Using ideas about friction is all about seeing the world through forces spectacles.

Looking through forces spectacles


In general we're concerned with identifying and labelling a force.

Let's talk forces


In the case of frictional forces, a force in which is exerted by one surface on another.

Friction


Children have a number of different ideas about forces. Research shows that many are both persistent and incorrect, particularly with respect to the effect on motion. This connection is particularly important for friction, which sometimes reduces motion, and sometimes enables it. We suggest that it's important to distinguish between the two, with a label for each:

  • Grip for getting things going, where there is no movement between the surfaces, and nothing gets warmed.
  • Slip for slowing things down, where there is warming.

These labels link well with everyday ideas of surfaces being slippy (there is very likely to be movement between the surfaces) or grippy(it's much less likely that there is movement).

To identify the forces you need to pay attention to the surfaces between which there might be movements.

The focus here is on one surface sliding over another, and not on moving through fluids, which results in drag. Drag is a much more complicated member of the forces which are grouped together under the frictional label, and is best dealt with separately (perhaps when you're working on air resistance or water resistance).

Teacher Tip: Keep in your mind that drag is rather different from grip or slip, even though all three are grouped as frictional forces.

This activity provides some physical experiences, that provide a hands-on experience to get children's minds-on in exploring the act of seeing the world through forces spectacles. This re-imagining, seeing through (special) forces spectacles is really important, as forces are not the kind of things you can see with conventional sight, even with a magnifying glass.

Friction


Teacher Tip: Grip and Slip, or even friction are always forces, so it's a really good idea to have to hand a small collection of force arrows, of three different sizes, to label different situations in front of you, or perhaps invite children to do so.

The physics ideas are explored in more detail in the Physics Narrative – here is an essential selection:

You have to re-imagine the world to re-describe it with forces: the forces spectacles are one way to identify and label this process of modelling.

Looking through forces spectacles


It is possible to build rather complicated descriptions rather easily. The idea in physics is to keep things simple.

Keeping it simple: modelling


If you'd like a quick reminder, or prefer your arguments graphically, you might also want to check:

An interactive diagram showing the process of looking through forces spectacles.

Re-imagining the world


An interactive diagram showing the process of re-imagining a held bag of shopping as seen through forces spectacles.

Modelling a simple situation


An interactive diagram showing how you can re-describe pushing a box in terms of grip and slip forces.

Pushing, grip and slip


Teacher Tip: Remember the key long term learning outcome here is that the force acting RightArrow change in motion. Here you're making a start by identifying the forces acting on an object. Much later children will need to learn how to combine these forces into a single force.

The main ideas to have to hand at all times

  • Grip accounts both for getting going and for preventing movement
  • Slip accounts for slowing down, when surfaces move past each other
  • Drag accounts for slowing down, when moving through a fluid

Teacher Tip: Find out more from the Physics Narrative.

Building this into other activities

Thinking about the difficulties of moving one surface over another provides plenty of opportunity for connections with other areas. There are many practical implications.

  • Transportation over land was much easier once stopped just dragging things(and started using rollers, wheels, ball bearings, lubricants)
  • Woven cloth is held together by the grip force exerted by warp on weft and by the grip force exerted by weft on warp
  • Knots rely on grip forces
  • Grip forces are reduced by lubrication: cooking oil on the hands reduces the chance of lifting that tin

You could invite children to write an invented story about the differing adventures of the puppet people slippy and grippy in their own world. Varying the world or how slippy or grippy they are allows many different ideas to be explored. Such counter-factual explorations are particularly good for exploring children's ideas.

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Discussion about instances

Force
Forces and Motion | Electricity and Magnetism

Discussion about instances

Classroom Activity for 5-11 11-14

What the Activity is for

Making up your own cases.

The purpose of this activity is to get children thinking and talking about where, and on what, forces might act in some everyday situations.

What to Prepare

  • copies of interesting scenarios, populated with your own images and starters

What Happens During this Activity

Groups of three working around a screen are best. You could, of course, just print out the completed instances.

There are some further examples here:

A rocket in the ground


A broken tree trunk


A car on the drive


A thrown object


You could, of course, prepare your own, by adapting this:

InsertCMR{MfBuildYourOwnDIPSupportCMRS}

You can get started here:

Build your own


Faster groups, or those revisiting the topic for revision, could be invited to make up their own examples using the tool.

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Cardboard arrows

Force
Forces and Motion | Electricity and Magnetism

Cardboard arrows

Classroom Activity for 5-11 11-14

What the Activity is for

The purpose of this activity is to help children to identify forces and give them a language to describe forces. Exploring pupil's ideas – and making them explicit – is a central feature of this introductory work.

What to Prepare

A circus of stations where forces can be identified, adapted to your own circumstances, for example:

  • a cup on a table
  • a mass hanging on a string
  • a floating block
  • a shoe on a slope
  • some foam under a heavy book
  • a stretched spring
  • something leaning against the wall
  • something on a weighing machine

Some force arrows:

  • enough force arrows, cut from sturdy card, to give several per group (see below)

Safety note: Be aware of the hazards of slipping and tripping. Don't use anything heavy enough to cause injury if it falls. Stretched out springs may cause injury if they fly back.

What Happens During this Activity

Pupils are invited to visit the circus stations in groups of three or four. They have to use their arrows to identify where there are forces acting and to explain to others in their group:

  • What exerts the force?
  • What kind of force is acting?
  • What is the force is acting on?
  • Where shall we place the arrows to show the force?

Paying attention to the interactions of the children will allow you to monitor the thinking which is going down a Wrong Track and to identify correct ideas to reinforce at a later stage, perhaps during a whole class discussion about each station.

You are likely to find opportunities to guide children on the exact positions of the force arrows and to encourage children to articulate the language of forces:

Teacher: Well done Martin, there is a force acting on the shoe in this direction. What is the name of this force?

Martin: err…friction, no, wait a minute…grip

Teacher: Good…now what's exerting the force?

As a spin-off from this activity you might be able to revisit each station to consider any sets of forces which seem to add to a resultant of zero. (Most stations are likely to be in equilibrium).

Resources

Download a copy of the force arrows to use with this activity.

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Looking through forces spectacles

Force
Forces and Motion | Electricity and Magnetism

Looking through forces spectacles - an activity

Classroom Activity for 5-11 11-14

What the Activity is for

Helping students to see the world in a new way.

The purpose of this activity is for children to make simplified drawings of each of the stations in the circus and to draw in the forces acting on the different objects.

What to Prepare

A set of stations to show forces in action. For example:

  • a cup on the table
  • a mass hanging on a string
  • a floating block
  • a shoe on a slope
  • some foam under a heavy book
  • a stretched spring
  • something leaning against the wall
  • something on a weighing machine

For this activity you might use the same circus of stations as for the Cardboard Arrows activity.

  • starter sheet, Looking through forces spectacles: Where are the forces?, which explains the task, gives an example and then offers children a framework for their own work (see below)

What Happens During this Activity

Pupils might be taken through the first example as a whole class. The main point to make being that the modelling process is aimed at producing a simplified sketch of the real situation at each station. The skill is to observe, think and then draw. Forces can be added as a last stage.

Resources

Download the support sheet / student worksheet for this activity.

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Lifting a tin

Friction
Forces and Motion | Electricity and Magnetism

Lifting a tin

Classroom Activity for 5-11

What the Activity is for

This lifting slippery objects activity helps children describe the world by:

  • recognising that grip forces are essential to completing some everyday tasks
  • recognising that grip forces vary as the surfaces vary

What to Prepare

  • friction hand puppet pairs: slippy and grippy (grippy can be made of reversed leather, slippy of parachute nylon – see what materials are to hand)
  • some large diameter tins or plastic bottles to lift – glass jars are tempting, but are just a disaster waiting to happen

What Happens During this Activity

Lift the tin by placing hands, whether encased in friction gloves or not, on either side of the tin, so that there are clearly surfaces in contact. Repeat for tins of different mass, and with different surfaces. Set it as a challenge, evolving with the discussion by using varying friction puppets

Teacher: Who can lift this tin?

Teacher: Now let's try changing who is doing the lifting: my little friend slippy will help us.

Emphasise, through discussion and diagram and active labelling with the cardboard arrows, that there is a grip force between the tin and the hand or glove, and that this can be large enough to lift the tin, or not.

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Visualising what happens at surfaces for grip and slip

Friction
Forces and Motion | Electricity and Magnetism

Visualising what happens at surfaces for grip and slip

Classroom Activity for 5-11

What the Activity is for

To help children describe the world by:

  • recognising that sliding rough surfaces past each other has a warming effect
  • recognising that grip forces vary as the surfaces vary

What to Prepare

  • friction hand puppet pairs: slippy and grippy (grippy can be made of reversed leather, slippy of parachute nylon – see what materials are to hand)
  • a varied collection of flat surfaces: carpet tiles, hardboard, linoleum
  • a pair of nail brushes

What Happens During this Activity

Model two surfaces slipping past each other using a pair of scrubbing brushes, with the long bristles lightly engaged, so that they are able to ping past each other as you move the brushes along. Draw attention to the pinging bristles. Ask how to prevent the surfaces sliding (push the brushes together more). Now you'll have grip and not slip. Draw attention to the lack of pinging in the bristles. Make links between the pinging and lack of pinging and expecting to feel something different. Allow the children to pull a friction puppet over a surface that's rough enough so that they feel warmth. Elicit this feeling by questioning, and link to the pinging.

Relate this to lifting the tin, feeling warmth when slip forces are at work, but not when grip forces are at work.

Teacher Tip: Slip forces are dissipative and warm things up. Grip forces are not, and don't warm things up.

You might go further by leading a discussion on phenomena where there is warming, and where not. This could be linked back to the hunt for slip and grip forces.

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Ordering slip or grip forces

Friction
Forces and Motion | Electricity and Magnetism

Ordering slip or grip forces

Classroom Activity for 5-11

What the Activity is for

To help children describe the world by:

  • relating physical experience of exerting force to representing that force with arrows
  • connecting the roughness of the surface to the size of the force

What to Prepare

  • friction hand puppet pairs: slippy and grippy (grippy can be made of reversed leather, slippy of parachute nylon – see what materials are to hand)
  • three pairs of rectangles of sandpaper, we'd suggest 400, 240, 120 grade
  • some large diameter tins or plastic bottles to lift – glass jars are tempting, but are just a disaster waiting to happen

What Happens During this Activity

Invite children to drag the matched pieces of sandpaper over each other, and label them with the three slip forces. Encourage the children to relate their labelling to the roughness of the surfaces, ascertained by rubbing their finger over the sandpaper and perhaps inspection of the surface by using a magnifying glass. You could profitably relate this to the roughness of the finger puppets. It's important to make links to the warming effect of the slip force, and this is something that can be felt rather well when you drag the grip or slip puppet over most surfaces.

Now repeat with the grip arrows. Here the trick is to order the sandpaper pairs by which are best at preventing relative movement. You can relate this to many examples where we do not want things to slide past each other: getting cars going – its best if the tire does not slip on the road. similarly for walking: you don't want the sole of the shoe to slide over the pavement.And for lifting tins, you don't want movement between the surface of the tin, and your hand.

We'd suggest not using more than three matched pairs of sandpaper surfaces, and not mixing and matching the surfaces, as this makes the labeling harder to do. However children could be allowed to explore by themselves, but may have to invent their own labelling arrows. They might find it hard to discriminate reliably, but so long as they are reasoning about the surfaces, and are moderate in their expectations, such explorations are likely to be worthwhile.

Up next

Everyday grip and slip

Friction
Forces and Motion | Electricity and Magnetism

Everyday grip and slip

Classroom Activity for 5-11

What the Activity is for

To help children describe the world by:

  • mixing and matching surfaces to see the effects on grip and slip
  • reasoning about the roughnesses of surfaces and the slip or grip forces

What to Prepare

  • friction hand puppet pairs: slippy and grippy (grippy can be made of reversed leather, slippy of parachute nylon – see what materials are to hand)
  • a varied collection of flat surfaces: carpet tiles, hardboard, linoleum

What Happens During this Activity

Drag a friction hand puppet over a variety of surfaces, and place them in order, according to the slip force experienced. Children might draw up a chart using slip force arrows of different lengths : prefer these to verbal descriptions or numbers.

You might extend this by trying out shoes with different sole designs on different surfaces. Again we'd suggest a report that used slip or grip arrows, depending on the experiment done (remember that slip is all about reducing movement between surfaces, grip is all about preventing movement between surfaces – and so is essential in allowing you to walk).

Teacher Tip: We'd suggest avoiding anything with wheels, as there are significant slip forces at the bearings (that's why these are often oiled and contain special bits of engineering, such as ball bearings) and these are very hard to analyse.

Up next

Getting a feeling for a one newton force

Force
Forces and Motion | Electricity and Magnetism

Getting a feeling for a one newton force

Classroom Activity for 5-11

What the Activity is for

To help children describe the world by acquiring a feeling for what a one newton slip force feels like.

What to Prepare

  • one newton force apparatus ( a 100 g apple, hidden in a box, that can be raised or lowered by string running over a pulley)
  • A cardboard force arrow, labelled 1 newton, attached ot the end of the string

What Happens During this Activity

You might rather lightly introduce the idea that the length of the force arrows is measured in newtons (depending on whether you've used this measure before), and use an everyday example so that children get a feel for the size of a one newton slip force. It happens that about half a cup full of tea, pushed across a desk, results in a slip force of about one newton. You might also have something suitably heavy in the classroom that pulling it across the floor results in a slip force of 10 newton – you'll need to try this out to find something.

Up next

Braking uses slip forces

Friction
Forces and Motion | Electricity and Magnetism

Braking uses slip forces

Classroom Activity for 5-11

What the Activity is for

To help children describe the world by:

  • emphasising that slip forces result in warming
  • recognising that mechanical braking relies on slip forces

What to Prepare

  • friction hand puppet pairs: slippy and grippy
  • a spinning disk to slow down

Teacher Tip: To check if the disk is appropriate, try spinning it up, then slowing it down with the slippy puppet: it should take more than 20 rotations. For the grippy puppet, it should be less than 2 rotations.

What Happens During this Activity

It may be that a discussion about bike brakes is the best way in, but this will depend on whether the children have and use bicycles. in other cases you may be better off with an image of formula one car brakes glowing. The link to the warming that's felt when slowing down a spinning disk with the hand gloves should be made. You'll need to experiment with the speed and surface in order to ensure that hands do not get burnt, but that the disk can be brought to a halt in a reasonable time (a few seconds).

Teacher Tip: You might stimulate a discussion about the results of braking using grip forces, or how braking is achieved using drag forces.

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