UNIT 12 (NATURAL SCIENCE 4º)

UNIT 12

THINGS: WHAT THEY ARE LIKE AND HOW THEY CHANGE

v WHAT ARE THINGS MADE OF?

·         MATTER

Matter is everything which occupies space and has a weight, or mass.

Matter can be in one of these states:

-          Solid: usually have a fixed shape and stay the same size.

-          Liquid: adapt their shape but do not expand. They flow.

-          Gas: expand and are invisible.

Every object and substance around us is made of matter. Most of them are made of a mixture of different types of matter (components). Mixtures and their components can be visible  or invisible.

·         THERE ARE MANY MIXTURES IN NATURE

Many things in nature are mixtures:

-          Air is a mixture of gases: oxygen, nitrogen, carbon dioxide…

-          Salt water is the water in seas and oceans, it contains salt.

-          Rocks are formed from minerals.

-          Milk contains water, sugars, proteins and fats.

·         MIXTURES CAN BE SEPARATED

A mixture can be separated into individual components.

How to separate mixtures

- Sieving using a sieve.

- Filtering using a filter.

v WHY DO THINGS MOVE?

·         FORCES CAUSE MOVEMENTS

A force is anything capable of moving a stationary object, or stopping a moving object.

An object can only move or stop if a force acts on it. If there is no force, the object cannot move.

·         SOME FORCES ACT THROUGH CONTACT

An object can move or change direction if someone or something touches it.

For example: a ball moves or change direction with the action of a racket, air, water…

·         SOME FORCES ACT AT A DISTANCE

Some forces act without touching the object:

-          Gravity: the Sun, the Earth and all celestial bodies exercise this force. All matter around them is attracted.

-          Magnetism: a magnet exercises a force at a distance. It attracts all objects around it that are made of iron.

v WHY DO THINGS DEFORM?

·         FORCES DEFORM THINGS

Solids can deform if a force acts on them. Some objects deform very little and can break and others deform and do not break.

·         RIGID AND DEFORMABLE MATERIALS

A rigid material is something which breaks and does not deform when a force acts on it. Ex: glass, granite, slate…

A deformable material is something which deforms and does not break when a force acts on it. Ex: plasticine, paper, rubber…

Deformable materials classify in two types:

-          Elastic: returns to its original shape when a force stops acting on it.

-          Plastic: stays deformed then a force stops acting on it.