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.
» 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.

» Copper block
» Brass block

» Ruler
» 1kg weight
» Retort stand
» Steel ball bearing
» String

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.
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

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.

Copper (pure metal) is softer than brass (alloy).

The hypothesis is accepted.

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