## Thursday, 19 February 2015

### 9.3.1 - Laboratory Activity : Investigating the difference in hardness of an alloy and a pure metal

 Laboratory Activity 9.3.1: Investigating the difference in hardness of an alloy and a pure metal
Aim: To understand the strength and hardness of alloys.
Problem statement: Is the hardness of alloys and pure metal are the same?
Hypothesis: Alloy is harder than pure metal.
Variable:
 » Fixed variable : Height and mass of the weight and the steel ball bearing. » Manipulated variable : Blocks of copper and brass. » Responding variable : Diameter of the dent.

 Material: » Copper block » Brass block Apparatus: » Ruler » 1kg weight » Retort stand » Steel ball bearing » String
Procedure:

The animation below shows the arrangement and the results of the experiment.

 1 A steel ball bearing is taped to a block of copper. 2 The weight is pulled to a height of 50 cm above the ball bearing. 3 The weight is released from the height of 50cm. 4 The diameter of the dent formed on the copper block is measured with a ruler and recorded. 5 Repeat step 1 – step 4 twice by using the different surface to get the average diameter rate. 6 The experiment is repeated by replacing the copper block with brass block.
Results:
 Blocks Test 1 Test 2 Test 3 Average Copper 3.2cm 3.1cm 3.3cm 3.2cm Brass 2.4cm 2.5cm 2.3cm 2.5cm
Discussion:
 ► Pure metal is soft. Therefore, the dent for copper is deeper and the diameter is bigger. ► Alloy is harder. Therefore, the dent for brass is shallow and the diameter is smaller.
Conclusion:
 ► Copper (pure metal) is softer than brass (alloy). ► The hypothesis is accepted.