Science

: Float or Sink

Approach: One to one

Level: Year 8 & year 4

Resources:	3 equal sized cubes:	softwood	marked A
		aluminium	B
		hardwood	C
	3 equal weight cuboids:	brass	marked D
		hardwood	E
		aluminium	F
	laminated card labelled "sink" and "float";
	plasticine, water in container,
	paper towels.

Questions / instructions:
In this activity you are going to find out if blocks float or sink in water.

% responses

1. If we say an object floats, what does it do?
If we say an object sinks, what does it do?

Good description of floating
sinking

87
85

96
91

If the student has no understanding of the terms explain that sinking means going to the bottom and floating means the object will stay at the surface of the water.
I'm going to give you three blocks which are the same size. I want you to tell me if you think they will sink or float in the water. Later you will be able to test them in water.

Give student the block marked A (softwood), and the laminated card.
2. Here is the first block.
Do you think it will sink or float?
Put it in that square on the card.

Predicted float

Give student the block marked B (aluminium).
3. Here is the second block.
Do you think it will sink or float?
Put it in that square on the card.

Predicted sink

Give student the block marked C (hardwood).
4. Here is the third block.
Do you think it will sink or float?
Put it in that square on the card.

Predicted float

5. Now test the blocks by putting them in the water.
    Do A first. Does block A float?
    Does block B float?
    Does block C float?

yes
no
yes

100
100
73

100
99
75

Point to the appropriate blocks as you ask:
6. Why do you think this one sank and this one floated?

Explanation related to density or weight/mass

Here are three more blocks.
This time they all weigh the same,
but have different shapes and sizes.

Give the student blocks
D (brass), E (hardwood), and F (aluminium).
7. Have a look at these three blocks and pick them up. Then tell me which you think will float and which will sink.
Put them in the squares on the card.

Predicted D will sink
E will float
F will sink

98
81
80

97
78
69

Now test the three blocks by putting them in the water. Which float and which sink?

Point to the appropriate blocks as you ask:
8. Why do you think this one sank and this one floated?

Explained as: density
size
material
NB all blocks are the same weight weight

2
10
50
50

16
14
51
35

Put the lump of plasticine in the water as you say:
9. Here is a lump of plasticine. See, it sinks. Do you think you can make it float?
Can you show me?

plasticine floated

Commentary:
Some of the hardwood blocks (C and E) became so waterlogged with repeated use that they sank.

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