MATERIALS AND THEIR PROPERTIES • Let us look closely at your book. • Does the paper bend easily, or is it stiff and hard to bend? • Can you see through it? • • You can use many words to describe your book. • Each word you use to describe an object is a physical property. • A physical property is anything you can observe about an object or substance using your senses of sight, touch, taste, smell and hearing. • Hardness • One physical property of a material is how hard or soft it is. this is called hardness. • A hard material will not be easily scratched or dented. • You can test the hardness of a material by scratching it with a nail. • • Magnetic • Some objects are attracted to magnets. This property is called magnetic. • Most objects that are magnetic are made of iron. • Iron is a type of metal. • Flexibility • Some materials bend when you apply a force to them. • Flexible materials return to their original shape when you stop applying the force. • Materials that are not flexible do not return to their original shape - they may also break when bent. • Flexibility is about how much a material can be bent without breaking and its ability to return • to its original shape. • • Can you think of reasons why some objects are made of flexible materials and others are not flexible? • Floating and sinking • • Take a ping pong ball and place it in a container of water. • What happens to the ball? • Does it stay at the top of the water or does it fall to the bottom? • • Some objects, like the ping pong ball, stay at the top, or float, when they are placed in water. • others, like a golf ball, fall to the bottom, or sink, when they are placed in water. • Whether an object floats or sinks depends on: • The material it is made of • Its shape • How much air it has in it • • Metal boats float because of its shape • • Cork floats because of the material it is made of. • • Life saver floats because it has air added to it. • Transparency • The girl in the picture is wearing safety goggles. • They protect her eyes when she is doing science experiments. • Goggles are made of metal would still protect her eyes, but she could not see through them. • • The plastic goggles are transparent. • Transparent means that light can pass through them easily. • Things that light cannot pass through are called opaque. • Some materials allow only some light to pass through them. They are translucent. • • How are transparent materials different from translucent materials? • Strength • • Imagine you are rock climbing with your friends. • You have never tried its before, but your friend assures you its safe. • He hands you a piece of cotton thread and asks you to tie it around your waste for safety. • How safe would you feel? • • The strength of a material is how much it can be pressed together or pulled apart without breaking. • • Cotton thread is not a strong material, it breaks easily. • It certainly would not be a good idea to rock climb with cotton thread. • • Rock climbers need equipment that is very strong. • They use metal clips and thick ropes.
