Lesson 1: Controlling forces

Learning objectives

For students to:

  • investigate forces and structures
  • understand the importance of wearing a seat belt
  • design, produce, use and modify a crash-test.

Resources

Additional materials may be required if the students undertake a more open-ended investigation or the production of more sophisticated crash test simulators.

Curriculum

Links to Science - 1.1, 1.4, 2.1, 2.2, 2.3, 3.1, 4a, 4c

Links to Design Technology - 1.1, 1.3, 1.4, 2a-h, 3b, 3c

Time

60 minutes for simple, directed investigation using pre-prepared materials.

Option is to extend the activity into an open-ended investigation which may take 2 or 3 lessons as required.


Seat belts and safety starter - 15 minutes

  • At the start of your lesson, get your class thinking about their current use of seat belts. Ask them to vote, using a show of hands, to indicate whether or not they use seat belts always, most of the time or never.
  • An optional spreadsheet (XLS 50KB) - new window is available which allows the votes to be entered quickly and viewed graphically. (The spreadsheet is locked so that users can change only the numbers of votes in each category. To customise the spreadsheet, first remove the protection (Tools menu) using the password seat belt.)
  • Ask whether their answers vary depending on whether they are in the front or the back of the car. What if there are two others on the back seat?
  • Explore responses in other typical situations - a short trip of under a few minutes, when travelling in a school coach or minibus, when in a taxi, or on a bus (school minibuses should have seat belts but public transport buses don't - this could prompt the discussion as to why not).
  • Finally, ask students to put their hands up again to show who still thinks they always wear a seat belt?
  • Do the adults that students travel with always wear seat belts?

Crash test video - 15 minutes

  • Show the short video clip, Seat belts and child restraints, which includes Transport Research Laboratory footage of belted and unbelted crash test dummies. Although it uses dummies, the video is still quite graphic and teachers should preview it to check the video's suitability for their group.
  • Teachers may wish to consider using a road safety campaign video, Three strikes (seat belts). This shows the shocking consequences for a driver who is in a collision but not wearing a seat belt. Teachers should preview this before using it with a class. (Please note that two versions of the video are available – pre and post watershed. We recommend you show the pre watershed version for this age group.)

Practical investigation: testing the effects of seat belts - 30 minutes

  • The activity shows the need to construct models where a real-life scenario is not possible. In this case, the models are far removed from real life but are intended to illustrate the principle.
  • This practical investigation can be expanded to fit the time and resources available. It also provides a good opportunity for collaboration between Science and Design & Technology departments in a cross-curricular approach. Teachers should perform a full risk assessment of this practical activity before undertaking it in class.
  • The activity gives students the opportunity to explore a range of approaches and to refine their methods in the light of test results.
  • Students have to design and build a crash test. This will include a 'vehicle' that will contain 'passengers' that can be restrained or not (to simulate seat belts or none). The vehicle is then used to simulate a collision with and without restraints. The investigation allows students to think creatively to devise a way of performing the crash tests that will give reliable and repeatable results.

Some suggested approaches are outlined below and student sheets are provided. If time and resources are available, students should be encouraged to take these as starting points and develop their own methods as they gain experience of performing the tests:

Crash test dummy

Students make a crash test dummy using plasticine.

The dummy in the vehicle will need to be deformable in an impact. The students must also be able to see and measure any deformation. A suitable material to make such a dummy would be plasticine, which will remain deformed after the impact. A simple cylinder could be made and formed as if seated in a vehicle. If time allows, use a more life-like form produced and seated in the vehicle.

Crash test vehicle

It may be possible to buy suitable toy vehicles but these will need to be robust enough to withstand the crash testing.

Alternatively, a simple test vehicle could be a rigid plastic sandwich box into which the dummy can be placed. A fixed cube provides a 'seat' for the dummy.

For the Design & Technology curriculum, students could be challenged to make different vehicles and test rigs.

The test could be extended to look at how vehicle design, such as crumple zones and energy-absorbent materials, can be used to help keep occupants safer.

Crash test

The vehicle and occupant need to be propelled into a solid surface. A simple way to achieve this is to slide the vehicle down an inclined ramp into a perpendicular surface. The angle of the ramp needs to be sufficient to give a considerable impact. Increasing the angle of the ramp will increase the speed of the impact.

Students may be extended by making calculations of the energy involved in the collisions using the formula:

Potential Energy (Joules) = mass of vehicle and passenger (kg) x vertical fall height (m) x 10 (m/s²)

Note that this is an estimation as energy will be lost to friction and the value of gravity has been rounded to 10m/s². Such a calculation would allow comparisons with the kinetic energy of real vehicles at different impact velocities.

Kinetic energy (Joules) = ½ x vehicle mass (kg) x velocity² (m/s)

Typical mass of a small car is 1000kg and 30mph = 13.4m/s

If a ramp is not available, the vehicle could be launched horizontally along the floor into a vertical barrier. A launcher can be improvised by stretching an elastic band between two legs of a stool. The elastic band is pulled back before the vehicle is 'loaded' and released. Using a force meter to pull the elastic band back set distances allows the force of the launcher to be estimated.

Restraint or no restraints

Students should perform several crash tests to investigate the effects of the 'passenger' being held with restraints or not restrained at all.

Their vehicle design will dictate the restraints that are used. In their simplest form, these could be thin strips of strong adhesive tape to represent the seat belt materials. The effectiveness of several configurations could be tested:

  • Three point restraint:
Three point restraint
  • Four point restraint:
Four point restraint
  • Lap belt (2 point restraint):
Two point restraint

Recording, analysing and presenting results

The investigation offers opportunities to record the results in a range of ways.

Students can measure the depth of indentations in the plasticine dummy and link these to the force and energy transfers in the impacts.

Using dataloggers, such as light gates or motion sensors, will allow accurate data to be collected on the velocity at impact and the accelerations involved. Teachers may wish this to extend into a mathematical analysis of the energy transfers.

Video cameras may be used to record the impact so that they can be reviewed in slow motion or to gather images used as part of a presentation of results.

Activity sheets

Two differentiated activity sheets are provided.

Controlling forces activity sheet 1 (PDF 240KB) - new window simply poses the open question that students need to investigate. It gives some outline guidance but encourages students to think creatively to investigate the problem.

Controlling forces activity sheet 2 (PDF 310KB) - new window gives a more detailed approach and a tabulated results sheet. It therefore offers more support for students.