# 01Exploring motion

Mf01TA of the Motion and force topic
• ## 01 Selecting and developing activitiesMf01TAnugget01 Suggestions

### Based on the Physics Narrative and the Teaching and Learning Issues

Ideas to emphasise here

• choosing a point of view
• focusing on increasing separation between the point of view and the object whose speed your measuring
• show that finding a speed is not simple and straightforward
• explicitly identifying the distance covered, and the length of time taken in order to figure out a speed
• distinguish between spinning on an axis and orbiting another object

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

Strategies for supporting learning

• introduced the idea that relative motion is the only motion, without causing indigestion
• differentiate the ways in which time is used
• telling stories about journeys, relating what's observed to the record that is made
• taking care about the use of arrows – for representing force, direction, and velocity or speed

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

• defining speed without relating it to increasing separation
• getting bogged down in units – e.g. mph, kilometres per hour, furlongs per fortnight

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.

• ## 02 A sequence to develop ideas about fallingMf01TAnugget02 Sequence

### Based on the Physics Narrative and the Teaching and Learning Issues

Falling, and perhaps also rising, are so common as occurrences that you'll perhaps need to make them a bit strange, to draw attention to particular features, in order to make the accounts of falling that you present seem worthwhile. Otherwise the phenomena may just seem to be obvious and not in need of any kind of explanation.

We'd strongly suggest that you restrict the situations you use for such introductory work to one dimension, so straight up and down. That'll mean selecting suitable examples, and so steering the discussion away from topics such as runaway cars and plummeting mountain bikes.

In some cases the way in which the falling happens is there to support enhanced movement in another direction: the advantage to tree seeds in falling slowly is precisely that so they can travel sideways further in the longer time enabled by the slower fall. However we suggest keeping the links at about this kind of level, and not trying to account for the path of the motion in any detail.

To extend the ideas, or even to see how securely children can make the links between the forces and the motion you might like to explore falling upwards, or rising in fluids. Apart from extending the ideas, the phenomena are interesting, often rather beautiful, and have many links.

Meeting reality: valuable experiences

• Dropping things in air: streamlined and irregularly shaped
• Dropping things in water: not into water
• Dropping things in a vacuum – at least a clip
• Rising in fluids, as a kind of inverse falling

A sequence for developing the idea

There are two essential elements interwoven here:

• a description of how the falling thing moves
• An account of why the falling thing has that motion

The end point, perhaps on later studies is to weave these two stories together, relating the changes in motion to the forces acting on the object. For your benefit, here is a summary for falling: in fluids and in a vacuum. In this sequence you'll start to develop the descriptions of the forces acting, and the changes in speeds, without necessarily bringing them together.

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

Here is one sequence for developing the idea:

How things fall

In this activity children assemble a collection of falling things, and start to describe the motion. Seeds look a fertile starting point here, but you might explore falling in all kinds of fluids, and for many kinds of objects.

These can be stories with or without data, but should mostly descriptive, exploring what might be causing the falling at each stage: so a focus on forces.

Falling all over the world

This explores the idea of falling on different continents . Apart from giving opportunities to amass a wide range of interesting examples, you can rather directly address the difficulties of what it means to fall down, as there is a known difficulty with the idea of down. Depicted on a globe, with the gravity arrows added, this can be both interesting and a powerful learning experience.

Cosmic falling

By starting just outside the atmosphere of Earth this activity enables you to tackle the known difficulty that many children are rather persistent in believing that the force of gravity only extends as far as the atmosphere. Extending the pull of gravity to other planets, and the solar system itself therefore provides a helpful corrective to this error. You should be prepared to deflect questions about why Earth does not fall into the Sun.

Falling together

This activity opens up the difficulties of relative motion, and gets to the heart of what it is to say quote{That's moving.} You might use a clip of a skydiver falling, as shot by another skydiver, or do some careful representing and consequent discussion.

Increasing and constant speeds

The difference between seeds and stones might be a natural starting point, but the end point is to describe (qualitatively) the changes in motion during a single fall. Few things fall at the same speed for the whole of their journey.

Slow motion falling

Some careful noticing and recording of simple objects falling through fluids other than air extends the opportunities to notice the changes in speed as the object falls, and to practice describing this change over the fall.

Bubbles

This is something of an interlude, or extension, or reinforcement. The process of falling up, as shown by bubbles in cooking oil, is the mirror of falling, also with variations in speed, and with some really interesting things to notice and record.

Not-falling

Not everything falls, and this activity provides a bridge to thinking about the forces acting on the supported objects.

Forces and falling

This will not be for everyone, but links the description of motion to the varying force acting. Children will meet this again later, so there is no need to squeeze it here.

Falling with ease

In this activity you can explore the idea of a natural motion.

Bigger and faster}

This activity is included in case the suggestion is made that bigger things must fall faster. It may be that you deflect the discussion, using some of the dialogue, rather than running it as a full-fledged activity.

Messages from research and practice: specific tripwires for this idea

The local nature of the idea of down is problematic, as is action at a distance. There are activities to tackle the former, but not the latter, which is probably best left to a later stage.

My speed is not your speed

All motion and therefore all speed is relative. Our everyday talking does not take this into consideration that this does lead difficulties if we're not careful. Be aware and be careful.

The idea of average speed

The idea of average speed can cause difficulty and it's probably worth being aware of this in order to avoid those difficulties rather than trying to address them explicitly at this stage.

Force equals motion: no motion equals no force

Force equals motion: motion equals force

It is early days, but it's worth starting out on the journey of trying to keep force and speed or velocity separate.

Teacher Tip: Force causes a change in motion, not a motion.

Separating ideas of gravity and atmosphere

Since the ideas of gravity, falling and down are inextricably linked and many people tend to associate the force of gravity only with actions on objects inside the atmosphere, this particular difficulty is probably worth tackling head-on. There are activities aimed at working with this difficulty.

Do heavier things fall faster?

There is an almost universal temptation to think that heavier things will fall faster. It's perhaps worth tackling this head-on somewhat later in the sequence.

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

You have to bring together three separate chains of thought, all of which most naturally use arrows to represent what is happening.

• the gravity force acting on an object
• what counts as down for an object
• the speed of the object

Looking through forces spectacles

It requires an act of imagination to re-describe the world in terms of forces acting on objects. This is a process that you only begin here, but it's probably good idea to be aware of the endpoint. This particularly true since we make extensive use of representing gravity forces using arrows.

Describing movement

Arrows are also used to describe motion, and provide a very concise way of doing so, so it's a good idea to keep the arrows rather separate in style.

• speeds can change
• forces change speeds
• what we call down depends on gravity
• gravity is an omnipresent force, found everywhere in the universe
• choosing particular snapshots of a motion is a fruitful way to describe the motion

Teacher Tip: Find out more from the Physics Narrative.

• ## 03 How things fallMf01TAnugget03 Activity

### Look out for falling objects

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

This is a focussing activity, that shows the wide variety of things that fall in the children's everyday environment, and begins to develop a range of descriptions for these falls.

What to prepare

• a frame for collecting lists of kinds of things that fall
• frames for developing different kinds of descriptions of falling

What happens during this activity

Encourage children to collect examples of many different kinds of things that fall and seek to categorise those in ways that make sense to them.

Compare and contrast the different falls, seeking to develop a qualitative or semi-quantitative description of each.

The idea of a semi-quantitative description is useful here: we want to build to talk about more or less speed and more or less force.

You're not after full quantification, with numbers and units: we are after comparing the values of the speed over a journey (in this case a fall) and perhaps, somewhat later, the values of the forces over that same journey.
• ## 04 Stories about fallingMf01TAnugget04 Activity

### What causes a fall? What can change how a fall happens?

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

The purpose of this activity is to begin to ascribe changes in a fall to the forces acting on the object. The forces are identified by hunting down interactions between the object and its environment. Initially we suggest producing two parallel descriptions: one about the forces and one about the speeds or velocities.

What to prepare

• a frame on which to describe the fall
• real objects to walk through a fall

What happens during this activity

Drop something( Choose something interesting, that will not break when it hits the floor). Then walk through the fall very slowly.

Ask for each of three or four stages:

Teacher: What is happening to the movement of (this falling thing) just here?

The three or four stages should be chosen wisely. We'd suggest:

1. just as you release the object
2. a short while after the object is released
3. just before the object hits the floor
4. as the object hits the floor

For each of the falls, we suggest completing a number of different descriptions – written, a cartoon drawing, a simplified diagram with arrows. For each kind of description, we'd suggest trying to draw out the difference between the descriptions of the motion and the causes the motion (that is between the forces and the speeds or velocities). Two parallel frames are useful here.

You might extend this activity by selecting a number of objects which vary in the way they travel through the air, such as:

• a soft toy
• a small stone
• a feather
• a sheet of paper
• a screwed up ball of paper

Alternatively you might provide each of a number of small groups with a pair of dissimilar objects, and a printed copy of the frame. Each group should walk through the fall of both of their objects and agree on descriptions to write on the frame (a shared frame, A3 or larger, helps to promote discussion). The faster-moving groups could the encouraged to compare and contrast the two falls and their descriptions of these falls.

• ## 05 Falling all over the worldMf01TAnugget05 Activity

### Different continent: different down

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

Children often have a very local understanding of the word down. In this simple and short activity we invite them to consider what down might mean for children in different places on this planet.

What to prepare

• a large globe, with the continents clearly marked
• a selection of small plastic toy people
• Some cardboard arrows labelled down, scaled for the people
• - ListItem{some cardboard force arrows labelled gravity
• a small stone
• a means of fixing the figures and arrows to the globe

What happens during this activity

Introduce the globe, and locate an individual toy person (perhaps named for somebody in the class) at your current location. Then build up to an experiment to determine the use of the word down.

Teacher: We're going to do very careful scientific experiment to figure out which way it down.

Teacher: We're going to concentrate on how we think about down. It's just the way things fall when we let them go. Let's try for this stone.

Teacher: So that's our experiment, now let's make a record of that on this globe.

Now reach for a labelled cardboard down arrow, and get someone from the class to add this arrow to the named plastic person.

Now imagine doing exactly the same experiment for a number toy figure on a different continent. First place the figure, and then do the thought experiment. You might make a better the fuss of the idea of a thought experiment, as being something that is done quite often in the sciences when you cannot actually go to a place or set up a situation to explore.

Alternatively, it is possible that you have a classroom link to a school in another country in which case a short video clip of their version of down might enliven the activity.

Teacher Tip: We advise against replacing the physical globe with any virtual representation of it on screen – the real three-dimensionality is important here.

Repeat for several continents, so that you have four or five small plastic figures and down arrows distributed across your globe.

As a next step you might add gravity arrows to each of the figure's locations, giving a reason such as:

Teacher: Gravity is the name that we give the force that makes things fall. wherever we see things falling, we expect to find the force of gravity at work. Things fall down, as we've seen. So the gravity arrows and the down arrows point in the same direction.

Finally you might produce a two-dimensional diagram of your globe, as a summary of what you've been doing.

It might help the transition to this diagram to cast a shadow of your three-dimensional globe and plastic figures on the wall in such a way that you can trace around it. Cunning forward planning will ensure that at least three figures and their arrows appear as clear shadows, and at very different locations on the globe.

• ## 06 Cosmic fallingMf01TAnugget06 Activity

### Down on different planets

What the activity is for

This a part of a suggested sequence:

A repertoire to develop the idea of falling

Here you can explore how the idea of down varies as you move from one planet to another, from one planetary system to another, from one star system to another, or from one galaxy to another. Down depends on the local gravity arrows.

There are significant links between this activity and the activity Falling all over the world which can be exploited.

What to prepare

• large spectacular images of clearly separated astronomical objects, perhaps shown using a data projector
• a selection of small plastic toy people – astronauts, if possible
• Some cardboard arrows labelled down, scaled for the people
• some cardboard force arrows labelled gravity
• Balls of different diameters to model planets

What happens during this activity

Teacher: If she dropped something, which way would it fall?

Then build on the answers to add a down arrow at this location. Move the astronaut around the astronomical object, repeating the question and discussions to leave a trail of down arrows around the astronomical object, at a variety of locations surrounding the object, at a number of distances from the centre.

As a next step you might add gravity arrows to each of the figure's locations, giving a reason such as:

Teacher: Gravity is the name that we give the force that makes things fall. Wherever we see things falling, we expect to find the force of gravity at work. Things fall down, as we've seen. So the gravity arrows and the down arrows point in the same direction.

We'd suggest repeating this for a number of distinctive astronomical objects, from planets, through asteroids, to the stars and moons.

At several stages you might add in a three-dimensional model using one of the balls and a number of astronomical figures. It all depends on how well you think the transition between the three-dimensional and two-dimensional is progressing.

As a summary of the whole exercise you might produce a two-dimensional diagram, where the central object is deliberately labelled as a number of astronomical objects explicitly. Surround this with a number of pairs of down and gravity arrows. Add astronomical figures as observers if that seems to make this thought experiments more concrete.

You might supplement this activity with some video clips of people dropping things in space: just make sure the people and the camera are not falling as well to avoid conceptual difficulties.
• ## 07 Falling togetherMf01TAnugget07 Activity

### Who is falling now?

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

The idea here is a bit subtle: we are working with the ideas that falling is simply a kind of motion, and that all motions are relative. So falling itself is relational. In particular if two things are both falling together, then there really is no relative motion. This is no different from being unsurprised to find that your passenger in the car is still beside you after several miles of journey: you are moving together – moving past the scenery, but not moving past each other.

What to prepare

• two soft toys
• a chair, ladder or balcony to give you a free-fall distance of around 2 metre

What happens during this activity

Start by telling a story about the two soft toys going on a journey, just walking across the table top, or through the undergrowth, or across the lawn. If they walk together, hand-in-hand, or side-by-side, then they're travelling at the same speed: they don't move apart or separate.

Then switch the kind of journey to one where they are falling, perhaps a kind of controlled falling in a lift to start off with. Again emphasise that they fall together – there is no relative motion.

Develop this to put them in free fall. Talk through their journey again from the point of view of first one and then the other. What will each one see? If technology permits you might equip one with a small video camera to record a fall. Practice will be essential, so that you do get a clear video of the other toy falling beside the first one.

You might supplement this with videos taken by skydivers, as they fall together.

To take it further, look for such a video where one skydiver opens his parachute. This really drives home the idea that motion is relative – the camerawoman keeps on falling, the other appears to shoot upwards – but of course that's just the relative motion in action.

With practice and for a bit of fun, you might manage to reproduce this with your soft toys and video camera.
• ## 08 Increasing and constant speedsMf01TAnugget08 Activity

### Same speed: changing speed

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

Here we revisit the walk-throughs of falling that were carried out earlier, with a careful emphasis on noticing the changing speed.

What to prepare

• a dandelion seed, or downy feather
• a frame for recording the speeds over the fall

What happens during this activity

Drop the Seed or Feather, and ask for a careful description of how it moves. Focus on the vertical movement – just the falling.

As before, split the motion into several stages.

1. just as the feather or seed is released
2. just after the feather or seed is released
3. a long time after the feather or seed is released
4. a very long time after the feather or seed is released

In this case would suggest that you avoid including the collision of the feather of the ground.

The idea behind choosing a feather or seed is that it very clearly speeds up and then drifts down at a more or less constant speed for the remainder of the fall. You could verify this, at least approximately, by making regular marks on a whiteboard past which the feather or seed falls. For the majority of the journey these will be evenly spaced, showing a constant speed.

As a summary of the discussion about the motion of this object, we suggest producing a large frame, with written descriptions of the speed and arrows to show the speed at each of the four stages.
• ## 09 Slow motion fallingMf01TAnugget09 Activity

### Arrested falling

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

This is a compare and contrast activity. Compare the fall of the seeds that have evolved to fall slowly with those that have not. As we already have a description of motion for the slow falling seeds, you might reasonably expect the faster falling seeds to show the same pattern, even though our eyes are not up to the task (although a high-speed camera is).

What to prepare

• sycamore seeds
• dandelion seeds
• a dried pea or bean, as a seed that does not float
• a frame for recording the speeds over the fall

What happens during this activity

Drop the dandelion seed, and summarise its motion over the four stages, drawing on the previous activity. We'd suggest here focusing on a description using arrows rather than words.

Drop the sycamore seed, and produce a summary of its motion. Its journey time is somewhat shorter, given that you have dropped it the same height, so the speeds will all be somewhat larger. You will need to develop the idea that the arrows will all be a bit longer through discussion, perhaps drawing on everyday journeys closer to home. the idea is essentially simple – that longer arrows lead to a shorter journey time: you cover more metres in each second.

Now might be the time to do a bit of predicting. Produce the bean seed and ask:

Teacher: We've got the patterns for the sycamore seeds and the dandelion seeds. What will the pattern look like for this been seed? In what ways will be different from the other two seeds?

You will need to run some discussion in order to develop the idea that the pattern is the same, but though there is some systematic variation across the seeds. Being able to line up all three completed frames will help you to establish the pattern, and to see the variation.

• ## 10 BubblesMf01TAnugget10 Activity

### Rising – the same physics as falling?

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

Here you are going to extend the description of motion that you have evolved for falling to things that rise. SO this is something of a reinforcement activity, showing how the ideas can be reused in a describing a new process.

What to prepare

• some cooling oil in a clear tall container
• a means of introducing bottles to the bottom of the cooking oil
• a Cartesian diver
• small stones, that fall through the oil
• a frame for recording the speeds over the fall or rise

What happens during this activity

Start by dropping the stones in the oil. Revisit the falling frames to record the changes in speed as the stone falls, again over the four stages:

1. just as the stone is released
2. just after the stone is released
3. a long time after the stone is released
4. just before the stone reaches the bottom

Make bubbles, and then ask for suggestions for completing the frames for the bubbles. We suggest the following four phases of such frames, as then the pattern will be directly comparable with the falling stones:

1. just as the bubble is released
2. just after the bubble is released
3. a long time after the bubble is released
4. just before the bubble reaches the top

Now complete the frames and compare the patterns. You should be able to flip one pattern to get another. The movement of rising bubbles are just the opposite of falling stones.

We'd suggest leaving the reason why this is the case as open at the moment – interesting, but not worth pursuing at the moment.

As an extension, you might consider using the Cartesian diver, which allows both rising and falling, and can therefore show both motions. You should avoid the temptation to explain how the Cartesian diver works – here it just provides a convenient process to study.
• ## 11 Not-fallingMf01TAnugget11 Activity

### Preventing falling

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

Here we start to look at forces that can oppose the gravity force and so prevent falling. This is a very simple quick introduction, and could be optional, but does open up the possibility of discussing some of the variation in speed over a fall.

What to prepare

• a soft toy, or other object to focus on
• some string
• some weak elastic
• some soft foam
• some cardboard gravity arrows
• some cardboard support arrows

What happens during this activity

Start by dropping the soft toy, this time focusing on the force of gravity that causes the falling. Building on this start, now open up a new question:

Teacher: How can we stop the soft toy falling?

Move the discussion towards providing some support for the soft toy: later these will be formalised as support forces, but that is a step beyond what you should aim to achieve here.

The endpoint of this discussion is simply to suggest that there could be forces which oppose the gravity force. These forces arise from the physical environment. It is useful to have a physical environment which distorts in order to provide the force, so we'd suggest starting with supporting this toy by using soft foam or by using weak elastic.

It is a further leap of the imagination to see the string as distorting to exert a force (a tension force), or to see the tabletop or floor as distorting to exert a force(a compression force). That is a step which may or may not prove useful for you to take.

The situation where there is no change in speed, because there is no speed at any time, is a special case of equilibrium: the forces acting on soft toy add up to zero.
• ## 12 Forces and fallingMf01TAnugget12 Activity

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

There you can see the universality of gravity: there will be force arrows on all falling objects.

What to prepare

• a wide variety of objects to drop (avoid anything fragile)
• a set of cardboard gravity arrows

What happens during this activity

Drop the objects one at the time, and walk through their falling journey. Choose any point on this walk-through other than the beginning or the end of the journey.

For each of the objects in turn, run a discussion such that the endpoint is adding a gravity force arrow to the object. Ensure that you have plenty of gravity force arrows so that at the end of the activity you can have an array of objects, displayed to show the gravity arrows on the objects at some stage during a fall (perhaps deliberately at various stages of the fall).
• ## 13 Falling with easeMf01TAnugget13 Activity

### Natural motion

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

Here you can make the point that an constrained free fall is similar to just floating along in a current (and perhaps to just drifting along in outer space). It's all kind of natural motion.

What to prepare

• images of pairs of objects falling
• images of pairs of objects floating in a current

What happens during this activity

Compare and contrast the images drawing on earlier work on relative motion to explore the idea of what might be an natural motion: that is something which objects to do by themselves when left alone in the environment.

This idea of a natural motion is a central one to develop later. Here it's just worth opening up the questions. It cuts to the core of understanding the universe as Newton did rather than as Aristotle did. And there's plenty of evidence that many people reason as Aristotle did in everyday life (because that's a successful way to reason), but fail to flip to reasoning like Newton did when engaging in more formal thinking in the sciences. Imagining motion with no forces acting turns out to be hard work, and to produce counter-intuitive results.
• ## 14 Bigger and fasterMf01TAnugget14 Activity

### Do heavier objects fall faster?

This a part of a suggested sequence:

A repertoire to develop the idea of falling

What the activity is for

The purpose of this activity is to challenge the commonly held, but mistaken, idea that heavier objects necessarily fall faster than lighter objects. The detailed reasoning is for the future, but a start on establishing some thinking along the right lines can be made now.

What to prepare

• two blocks of wood, one at least double the mass of the other
• two items of soft fruit – we'd suggest a melon and a peach
• a chair, ladder or balcony to give you a free-fall distance of at least 2 metre (more is better, but messier)

What happens during this activity

Encourage children to predict which of two blocks will hit the ground first when released together from the same height. Allowing children to feel the different masses before release is important. Encouraging a dialogue about which of the two is being pulled with a greater force is also important.

It is likely that a range of predictions will emerge from the class. Invite children to share their reasoning for these predictions before they see the event.

Safety note: Take care when dropping heavy objects. Bouncing masses can be dangerous, as indeed can be falling ones. Two blocks of wood, about 200 gram and 800 gram, will do the trick and will not be adversely affected by wind resistance over a fall of a few metres.

Dropping a melon and a peach together from a significant height (a second floor window is likely to prove suitable) will provide memorable proof that the mass of an object makes no difference to the rate of fall.

You should be aware of the mess which will be created by this demonstration. This can be minimised by placing a large plastic sheet on the ground. You also need to be aware of the fact that from too small a height the fruits will remain intact (no sensational explosion), while if they are dropped from too great a height air resistance might become significant and the two will not reach the ground simultaneously. The moral here is that practice makes perfect. This is certainly one of those demonstrations that makes physics fun and simply unforgettable!

You might follow this up with a discussion around interesting images, perhaps like this one:

A warning sign

•