Activity 2. To measure the volume of an irregularly shaped object using an overflow can.
Equipment Overflow can, graduated cylinder, stone, thread, water
Overflow can
Procedure 1. Make sure the overflow can is filled to the brim. 2. Tie the thread around the stone and lower it into the can. 3. Collect the water that overflows into the graduated cylinder. 4. Carefully read the volume in the graduated cylinder. This is equal to the volume of the stone.
Fig. 16 Measuring the volume of a large irregularly shaped object.
27.8 Accuracy and precision
When scientists measure something they usually take more than one reading. When the readings are not all the same, an average may be taken as the correct value. The table here shows three readings of body temperature. The average value was calculated as 37.1o
C. To decide if this
value is correct we must consider the accuracy and precision of the measurements. These were discussed in Chapter 4: Scientific Investigations.
Reading Reading 1
Reading 2 Reading 3 Average
Temperature 36.9o
37.0o 37.4o 37.1o
In the table above the average temperature of 37.1o
C C C C
C may be accurate but the readings are not
very precise because they are all different to each other. We often have many instruments to choose from when making measurements. Choosing the most suitable instrument depends on a number of things including accuracy and precision.
