Lesson 3 Relationships

Stretching a spring What is the input variable here and what is the outcome variable?

Variables Input variable (What we change.) Outcome variable (What we measure.)

Activity 1 Stretching a spring Hang the spring on a stand. Clamp a ruler or measuring scale behind it so that the bottom of the spring is just at the 0 cm mark on the ruler. Now if the spring is pulled on gently, you can measure how far it stretches.

Activity 1 Stretching a spring Hang a mass hanger on the spring. The mass hanger weighs 100 g. Read off how much stretch this has put on the spring. Write the results in the table on your Notesheet.

Activity 1 Stretching a spring Repeat the process by adding a 100 g mass to the hanger. This new mass is now 200 g (100 g from the hanger plus 100 g mass). Record the new stretch of the spring. Keep adding 100 g masses, one at a time up to a total of 500 g. This will be four masses plus the hanger. Each time you add a mass, record the new stretch in your table.

What variable do you put along the bottom line of the graph paper? Input ( Mass / g ) What variable goes up the side? Outcome ( Stretch / cm )

Plotting the graph Mass / g Stretch/cm Outcome Input

Write a sentence describing what kind of relationship your graph shows. Use the words variable, input and outcome.

If you added two more masses, making the total mass 700 g, what do you think the stretch of the spring would be? How did you decide?

Heating oil When oil is thick it takes a long time for to go through a funnel. When it is thin, it runs through quickly. You can measure the time taken for oil to run through a funnel. The time taken will be a measure of its thickness. The proper word for this is ‘viscosity’.

Heating oil You will find out how fast a steel ball fall through a test tube of oil over a range of temperatures. What will you use to measure temperature? What will you use to measure time?

Heating oil Heat the test tube in a water bath and then measure and record the time for the steel ball to fall through 10cm of oil. Do the experiment at room temperature and then repeat the experiment after heating the oil to about 30°, 40°, 50° and 60°C.

Heating oil Input variable (What we change.) Outcome variable (What we measure.)

Plotting the graph Input variable (What we change.) This goes along the bottom line of the graph. Outcome variable (What we measure.) This goes up the side.

Prediction From your results could you say what shape the graph will be? Now plot your graph. Was your prediction right? How did you make your prediction?

Write a sentence to describe the relationship between variables shown by this graph.

Look at the two graphs. In what ways are the graphs similar? How are the two graphs different? Which graph do you think would give the best predictions of what would happen if you kept increasing the input variables in the investigations? Why?

Thinking Back Could you easily identify the inputs and outcome variables in each activity? Which ones were difficult? Why?

Bridging. What other science activities have you done recently? What were the input and outcome variables? What sort of relationships were there?