Wanganui and Wellington water

This task is about planning a fair test.

Question

soap powder, water from wellington and wanganui
 
Some students wanted to compare tap water from Wanganui and Wellington to find out which makes bubbles more easily with soap powder.
 
a)  Students want to do a "fair test". They need to make sure that all the following are kept the same EXCEPT the:

    • amount of soap powder used

    • number of shakes given to the container with the soap powder and water.

    • temperature of the water.

    • where the water came from.

    • amount of water used.

Question 1Change answer

b)  The students did the experiment twice.
     Why did they do this?