Acceleration
Forces and Motion

Accumulating changes - Teaching approaches

Classroom Activity for 14-16

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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Where to next?

Acceleration
Forces and Motion

Where to next?

Classroom Activity for 14-16

What the Activity is for

Using accumulations and vectors to predict routes.

The whole apparatus of Newton's second law (dynamics – causes of changes in motion) and kinematics (describing the motion) is about being able to predict motion – for example, well enough to put men on the Moon, or to land a ship at the correct location.

So using calculated vectors to work out where something will be, when it'll be there, and what speed it'll be moving at focus on the core successes of this invented world in mimicking the lived-in world.

What to Prepare

  • an ordered set of vectors, able to be arranged tip to tail by translation, without being rotated (see below)
  • access to the software tool for exploring accumulations, QWA (see below)
  • a diagram of the whole schema of dynamics and kinematics (see below)

What Happens During this Activity

Show the ordered collection of displacement vectors, reviewing what a displacement vector indicates in passing.

Then ask how they can tell where they'll be after each interval, if the vectors predict their route.

Assemble the vectors tip to tail, in order, to predict the path.

Teacher: Now, how are the displacement vectors found?

Review the whole process

  • Velocity telling displacement how to change.
  • Acceleration telling velocity how to change.
  • Forcemass setting the acceleration.

You may choose to use the support sheet to help.

You might then use the interactive tool, QWA, to revise each of the separate stages of accumulation.

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Relative motion and PoV

Acceleration
Forces and Motion

Relative motion and PoV

Classroom Activity for 14-16

What the Activity is for

Here students get to see a process from a second point of view, moving with respect to the first, and so get practice in putting themselves in another's shoes.

The ability to see the situation from several different points of view is essential to developing fluency in describing motion. It's also a very useful precursor to the approach developed in the Physics Narrative of episode 04, although we suggest that you avoid colliding the vehicles here, so avoiding an interaction.

What to Prepare

  • two small video cameras
  • two freely running vehicles
  • a screen to display clips, preferably side by side

What Happens During this Activity

We suggest restarting the relative motions to one line, rather than a plane, or higher dimensions: so run the vehicles either parallel or anti-parallel to one another. In either case there should be relative motion between the two. Mount one video camera on each vehicle pointing at right angles to the motion, so that it will see the other vehicle pass. Pay attention to the backgrounds of both cameras, so that there is something significant to be seen as they scan past. We suggest using a clap or other percussive noise to be captured by the running video cameras, as a means of synchronising the two recordings.

Before showing the clips it's worth asking the students to agree on what the clips will show, expecting them to translate from their point of view.

You might even exploit the Alice, Bob and Charlie routine in the Physics Narrative to discuss the three different points of view.

The experiment might be followed up by other clips from the moving object (there are many posted on the internet, or students may have some, as a result of the spread of sports-cams), and ask the students to describe the motion from a different point of view (note: a description does not have to be restricted to words).

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Analysing motion by hand

Acceleration
Forces and Motion

Analysing motion by hand

Classroom Activity for 14-16

What the Activity is for

Although computer-mediated analysis may dominate your practical work, there is a case for a moderate amount of work close up with the data. For this purpose we recommend the use of offset tables and multiple-exposure photographs. These are simpler to deal with, away from the computer, where high-frame-rate digital cameras have more or less displaced this as a practical measurement technique. Nevertheless, we'd encourage you to demonstrate such an image being made in the laboratory, as perhaps the most direct and simple way to explain how such images come to be.

There is also a physical immediacy to the multiple-exposure photographs, as they present a trace of the motion, visible all at once, so making strong links with the graphical representation that is missing from the step-by-step presentation of the data when using video clips.

What to Prepare

  • a ruler
  • a pencil
  • a rubber
  • some printed prepared grids (see below)

What Happens During this Activity

Introduce the multiple-exposure photographs, perhaps by putting an impressive one on a large screen. Talk through how these tell a story of the motion, and how students could tell the speed between any two (selected) points.

Show the image they are to work on, and bring to their attention the essential scaling factors that connect this representation to the original phenomenon (a measure of length on the image and the interval between the images).

Now introduce the offset sheets, making clear which columns are for the data, and which calculated. Finally set the challenge of producing good displacement–time and velocity–time graphs from the data.

This will be time-consuming, and you'll need to check with your mathematics-teaching colleagues, to see what their graph-plotting skills are like. It's probable that extracting and processing the data are the key activities here, so you may wish to use computational support for the plotting phase. However, we'd not recommend using a spreadsheet to process the data unless you can reproduce the offset cells of the support sheet. We think that these are important to keep track of the intervals.

Resources

Download the support sheet / student worksheet for this activity.

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GPS-enabled stories of motion

Acceleration
Forces and Motion

GPS-enabled stories of motion

Classroom Activity for 14-16

What the Activity is for

Many students will probably be carrying a GPS with them embedded in a mobile phone or other electronic device. These can be explored, together with freely available visualisation tools to bring some stores of everyday motion into their physics classroom. Depending on your class and personal style, you might offer a reward for the most interesting track.

What to Prepare

  • a set of GPX tracks downloaded from the students' mobile devices (You might provide a small library of GPX files for those who cannot make their own tracks – there are many such files on the internet, often placed there by runners, cyclists, or explorers.)
  • one large screen or many small screens
  • access to gpsvisualaiser.com, or equivalent

What Happens During this Activity

You can, of course, use this either as a teacher-focused activity with a large screen, and a single computer, or a student-focused activity, where students use the visualisation tools for themselves. Since at least some of the tools are freely available on the internet, you might even ask students to process their tracks before class starts.

The range of things that students might consider will need to be adapted to the local environment. In a rural school located in undulating countryside, where some are known to cycle, a sample challenge might be:

Teacher: Can you show me some graphs that link the gradient of the hill to the speed you cycle at, on the way to school? Is your average speed higher on the way home?

But the emphasis ought to be on producing an illuminating trace, with some creative thinking going into the motions and into the displays. The best ones, suitably annotated, ought to be worthy of some wall space for a few weeks following the activity.

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Graphical stories of motion

Acceleration
Forces and Motion

Graphical stories of motion

Classroom Activity for 14-16

What the Activity is for

Students can walk-out target graphs, and so obtain a real understanding of what the story behind the graph is. The translation is between the graphical and the physical. The same technology also allows variations, as it's the act of translation that provides the key to understanding: you can phone a friend and have them reconstruct a graph just from a verbal description, walk out a graph just from the verbal description or walk out a graph from a set of vectors. Tune the translation to suit the class and what you want them to learn. In all cases the screen and display can provide a common reference point for the discussion. In this activity it's the graph that is the core representation.

What to Prepare

  • a motion sensor and display
  • a series of graphs to mimic, or other instructions

What Happens During this Activity

Here is one variation. Set up the motion sensor, directed at a space where there will be few stray reflections (important for those sensors that emit and detect pulses of radiation), and load up a target graph. Invite a student forward to walk-out the graph, using their torso as the target for the sensor and therefore the object whose motion is graphed.

Teacher: I'd like you to see if you can walk as this graph shows, to make another graph exactly like this one.

We'd expect you to need to use several prepared graphs, each with several students, to establish the pattern that you're focusing on through your choice of graph.

There are alternatives, some of which might be used as follow up.

Teacher: Here's a graph. Get your friend to redraw the graph, without showing it to them. Imagine you're phoning the friend.

Teacher: Here are a set of vectors, showing how the velocity changes. Walk out the graph of the motion shown by these vectors.

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Formative questions

Force
Forces and Motion

Formative questions

Classroom Activity for 14-16

What the Activity is for

Select some questions that can be used to explore students' understandings of these rather difficult ideas. Because the shift from the idea that force causes motion to force causes a change in motion is hard, it's worth selecting questions that promote discussion of this very particular point.

There are many questions available on this topic, and in a variety of formats, from discussion about instances, through predict, observe, explain, to multiple choice in two and three step formats (first step – answer; second step – reason; third step – confidence). Many have been developed from research projects, and extensively trialled.

The questions should be selected to help learning, so for their formative value, rather than to make summative judgements.

What to Prepare

  • printed copies of the questions

What Happens During this Activity

Students might be set some preparatory work, but the essence is to get a discussion going, and so allow space to fully explore the ideas. You'll need to create an environment where it's acceptable to make mistakes and engage in exploratory talk in order to ensure that they have got a grip on the ideas, and that you have the chance to find out where they are still uncertain.

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