Open a pencil case and you will find wooden pencils, steel clips, plastic rulers, and rubber erasers, each made of a different material.
Materials differ in how hard they are, how much light passes through them, whether they stick to a magnet, and whether they float.
That is why windows are made of glass that lets light through and erasers of soft rubber: we pick a material whose properties suit the job.
Pick a material to see its four properties side by side, and the lower picture shows whether an object made of it floats or sinks.
Comparing materials
Just the things in a pencil case are made of different materials: a wooden pencil, a steel clip, a plastic ruler, a rubber eraser. Each material differs in how hard it is, how much light gets through, whether it sticks to a magnet, and whether it floats, so when we make something we choose a material with the right properties for the job. Windows are glass because light passes through it, and erasers are rubber because it is soft and treats the paper gently. That is the reason to line up all four properties before choosing a material.
seegongsik.com
Properties by material: hardness, clarity, sticks to a magnet, floats
Pick a material with a button, and the left side shows a square in that material's colour along with the object used in the test. The clearer the material, the more the square lets the background show through, as with glass. On the right, read hardness and clarity from how far each bar is filled, and read sticking to a magnet and floating from O or X. The lower picture puts the same object in water: a floating object sits at the surface with only part of it under water, and a sinking object rests on the bottom.
🔍 Every material is different
①Wood is light and floats, so it is used to build boats and rafts
②Iron is hard and sticks to a magnet, but metals like aluminium and copper do not
③Glass is clear so light passes through, but it breaks easily
④Rubber stretches and shrinks back, so it is used for erasers and gloves
⑤Plastic is light and easy to make into many shapes
Float or sink?
It is easy to think every metal sticks to a magnet, but only a few metals such as iron, nickel, and cobalt do. An aluminium can or a copper wire is metal yet does not stick, which is why the picture uses iron to stand for metal. Rubber does not always float either: a rubber eraser sinks, and a rubber ball floats only because it has air inside. Not everything clear is glass, so naming a material from a single property often goes wrong.
seegongsik.com
Whether an object made of the chosen material floats or sinks in water
💡 Why do things float or sink?
①An object lighter than the same amount of water floats
②An object heavier than the same amount of water sinks
③The wooden block and the plastic bottle cap float, while the iron nail, glass marble, and rubber eraser sink
④An object only a little lighter than water floats almost completely under the surface
Summary
Properties of materials
Material → Hardness + Clarity + Sticks to magnet + Floats
Looking at all four together lets you tell materials apart
When things float
Lighter than the same amount of water → floats / Heavier → sinks
Objects whose weight for the same size (density) is less than water's float
🎯 Key points
①Materials differ in hardness, clarity, sticking to a magnet, and floating
②Only some metals, such as iron, nickel, and cobalt, stick to a magnet
③Objects lighter than the same amount of water float, and heavier ones sink
④We make things from materials whose properties suit the job
⑤Cups of the same shape made of glass, plastic, or paper all have different properties
Examples and Unit Test
Example 1
Among a wooden stick, an iron nail, and a plastic ruler, which one sticks to a magnet?
1
Only some metals, such as iron, nickel, and cobalt, stick to a magnet.
2
Wood and plastic do not stick to a magnet, but a nail made of iron does.
▸ The iron nail
Aluminium and copper are metals but do not stick, so check whether it is iron, not just whether it is metal.
Example 2
What happens to a wooden block and an iron nail when you put them in water?
1
For the same size, an object lighter than water floats and one heavier than water sinks.
2
Wood is lighter than water, so it floats, and iron is much heavier, so it sinks to the bottom.
▸ The wooden block floats, and the iron nail sinks
Pick wood and then iron in the lower picture to see floating and sinking right away.
Unit-test style
Which statement about the properties of materials is correct?
①Every object floats in water
②Iron is hard and sticks to a magnet
③Light cannot pass through glass
④Wood sticks well to a magnet
⑤All materials have the same properties
▸ ② Iron is hard and sticks to a magnet
1
Iron is a hard metal, and it sticks to a magnet.
2
Some objects, like an iron nail or a glass marble, sink (①), glass is clear and lets light through (③), wood does not stick to a magnet (④), and each material has its own properties (⑤).