NSW Syllabuses

# STEM Stage 2 - Activity 3

#### Description of activity

Students design and make a simple object that will allow them to investigate how the stretch of a rubber band will affect the distance it can travel (a rubber-band launcher). Students collect and record data to determine the relationship between these two factors.

This activity will take approximately 1 hour.

#### Context

Force can be defined as a push, a pull or a twist. A force acting on an object will result in a change in movement – starting, stopping or changing direction. This activity allows students to determine the relationship between the size of a force applied to an object and the distance that object will travel.

#### Outcomes

Skills

ST2-4WS investigates their questions and predictions by analysing collected data, suggesting explanations for their findings, and communicating and reflecting on the processes undertaken
ST2-5WT applies a design process and uses a range of tools, equipment, materials and techniques to produce solutions that address specific design criteria
MA2-1WM uses appropriate terminology to describe, and symbols to represent, mathematical ideas
MA2-3WM checks the accuracy of a statement and explains the reasoning used

Knowledge and understanding

ST2-7PW describes everyday interactions between objects that result from contact and non-contact forces
MA2-9MG measures, records, compares and estimates lengths, distances and perimeters in metres, centimetres and millimetres, and measures, compares and records temperatures
MA2-18SP selects appropriate methods to collect data, and constructs, compares, interprets and evaluates data displays, including tables, picture graphs and column graphs
INS2.3 makes positive contributions in group activities
PSS2.5 uses a range of problem-solving strategies

#### Resources

• Rubber bands
• Ruler, metre rule or tape measure
• Markers, eg sticky dots, small plastic discs
• Safety goggles or sunglasses

#### Work, health and safety

Check relevant Work, health and safety guidelines.
Students wear a pair of safety goggles or sunglasses to protect their eyes.

#### Evidence of work for assessment purposes

• Written procedure describing how the experiment was carried out
• Labelled photo(s) or diagram of the rubber-band launcher
• Data expressed in a table and column or picture graph
• Statement describing the relationship, if any, between the forces applied and the distance travelled

#### STEM teaching and learning activities

See suggestions concerning student involvement in practical activities.

Students may get excited at the prospect of launching rubber bands at people. It should be emphasised that a Safety Officer can be made responsible to make sure that everyone in their group behaves and does not put anyone in the group or in another group in danger. As everyone can be the Safety Officer for at least part of the time, everyone is responsible.

• Students design and make a piece of equipment that can measure the extension of a rubber-band, after stretching, and then launch it.
• Students plan a fair test that will provide data linking how far a rubber band is stretched and the distance it travels.
• Students determine how much the rubber band will be stretched. This will depend on the size and strength of the rubber band. For example, students may stretch the rubber band by one cm, launch it and then measure and record the distance the rubber band travelled. Increasing the stretch by another one cm and repeating the event; keep doing this until it will not stretch any more without breaking. Students should aim for a minimum of five different amounts of stretch length.
• Each student in the group takes a turn at each role. In this experiment this may mean that one experimenter will carry out the experiment at one-cm extension, two-cm extension, three-cm extension etc. The others perform their assigned tasks. Once the initial data has been collected, students swap roles and collect a new set of the same data. This not only ensures that each student plays an active part in the experiment and learns every role, but it also gathers several sets of the same data that can be averaged and reduces the effect of differences between experimenters and readings.

• The class may not have studied averages or arithmetic means yet, but it is a way of getting a middle value and overcoming individual differences. The technique of repeating trials and taking the average should be common practice whenever recording values in an experiment.
• Students transfer the 'averaged' data from the table into a column graph or pictograph. From this, students should be able to see the relationship between stretch and distance travelled.
• Discuss the results and the relationship they indicate.

#### Vocabulary list

Average – or arithmetic mean of a list of numbers is the sum of the data values divided by the number of numbers in the list
Elastic – the ability to return to the original shape or size after being stretched
Launch – to start or set in motion
Trial – a test or examination of evidence

#### Key inquiry questions

What is a rubber-band launcher?
The two requirements of this piece of equipment are that it can launch a rubber band when the rubber band is pulled back/stretched and that the amount of pull back/extension/size of rubber band can be measured. Probably the simplest way is to place the rubber band on the end of a ruler, pull back on the rubber band, measure how far it extends and let go.

How will you make this a fair test?
When students plan a fair test they ensure that:

• only one thing is changed – in this case how far the rubber band is stretched
• one thing is measured – in this case the distance the rubber band travels
• all other factors remain constant/the same – in this case:
• where the experiment is done, to eliminate the effect of wind
• the angle at which the rubber band is launched
• the way it is launched
• the point from which the landed rubber band is measured
• the part of the landed rubber band that is measured each time it is measured.
• If these, and possibly more, factors are not controlled the results obtained will not be reliable.

The following statements outline some common preconceived ideas that many students hold, which are scientifically inaccurate and may impede student understanding.

Objects stop moving because they run out of energy
Just as a force is needed to start motion, a force is also needed to stop motion. We used energy to stretch the rubber band. This energy provided the rubber band with a level of force that can be converted back into movement. As the rubber band is released this stored energy is converted into motion (kinetic) energy, but the force of gravity (drawing the rubber band to the ground) and frictional forces (caused by air resistance) act in directions that will oppose the force that was applied. Thus the rubber band will slow down and drop to the earth.

Force and energy are the same thing
The terms 'force' and 'energy' refer to different concepts. In the context of this experiment, energy is used to stretch the rubber band. This energy is transformed into potential energy in the rubber band and a force is present because the rubber band has been stretched.

Notes on safety
Clearly, safety is an important issue. Teachers are best placed to determine any restrictions or modifications that may need to be implemented. Some teachers may extend the activity by posing a task for students to design a safe method or 'range' in which to carry out the experiment.

#### Adjustments for the diversity of learners

Focusing on group work will help address and enhance the PDHPE outcomes INS2.3; PSS2.5

For those students who are able, plot a line graph. This will make the relationship between the amount of stretch and the distance travelled clearer.

#### Review

In this STEM activity your students have explored the concepts of forces and energy. Understanding these concepts is essential for their future studies in Physics, Chemistry and Technology. Force and energy are the foundation of Newton's Three Laws of Motion and the First Law of Thermodynamics which states that: energy is neither created nor destroyed, only changed from one form to another.

Students' practical experiences in designing equipment, planning and carrying out an experiment, collecting, recording and interpreting data develop skills essential for success in any Science, Mathematics or Technology course as they enable students to gather data accurately, analyse that data and make informed decisions based on this data.