Gases

A gas is one of the three states of matter .

Gases fact file Gases can be compressed (this means they are squashy) Gases flow easily Gases always completely fill any container they are placed in The most common gas is called air Some gases, like methane, burn easily and are used as fuels for heating

This table shows the names and uses of some common gases

Name of gas	Some useful facts	Uses
Air	Air is the gas all around us. It is a mixture of several different gases, mainly nitrogen and oxygen.	Without air we cannot breath and fires won’t burn. It supports balloons and aeroplanes.
Natural Gas	Natural gas comes from the ground. It burns easily (flammable)	Natural gas is used as a fuel for heating.
Oxygen	About 1/5 of the air is oxygen. Without oxygen we cannot breath and fires wont burn. Oxygen is produced by plants (during photosynthesis).	Oxygen is used in hospitals to help us breathe. It also used in welding and as rocket fuel.
Carbon dioxide	Carbon dioxide is needed by plants when they make food (during photosynthesis). All living organisms breath out carbon dioxide when they make energy (from food).	Carbon dioxide is the gas in fizzy drinks. It is also used in fire extinguishers.
Nitrogen	Nitrogen is the main gas in air. (about 80%)	Nitrogen is used to make plant food (fertilizer) and is also in explosives.
Water vapour	Water vapour is formed when water evaporates. There is lots of water vapour in the air we breathe out.	When water vapour in the air cools down it forms clouds.
Helium	There is a small amount of helium in the air. It is a very light gas and is used in balloons to help them float	In balloons to help them float
Argon	There is a small amount of argon in the air.	Argon is the gas inside electric light bulbs

Quick test

Which gas is used up when things burn?        Answer       Oxygen     

Which can get compressed tghe most, a solid, liquid or gas?        Answer       Gas   

Name the most common gas ?        Answer       Air   

What gas is needed by plants to make food?        Answer       Carbon dioxide   

What gas is often put in fire extinuishers?        Answer       Carbon dioxide   

Air does not weigh anything. True or False ?        Answer       False. The air in your bedroom would weigh about 50kg   

source : http://www.mikecurtis.org.uk

Electric Circuits

Simple Circuits

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When we use wires to connect a battery with a bulb (or buzzer etc) and the bulb lights then we have a circuit

The inside of a wire is made of COPPER (which is a good conductor of electricity)
The copper wire is covered with coloured plastic (which is an insulator).

Example Here is a circuit where a battery (sometimes called a cell) is connected to a bulb using wires. Below is a circuit diagram of the same circuit using the correct symbols

The Cell  Circuit symbol The cell has a voltage which makes an electric current flow around the circuit. The higher the voltage the greater the current A 'battery' of cells Symbol for a battery Several cells joined together form a battery.

The bulb

Circuit symbol

The BULB

A light bulb has a thin metal filament, often made out of tungsten, which glows very hot when an electric current flows through it. If we use a higher voltage more current will flow and the filament gets hotter and glows brighter. Too much current makes the filament melt (and the bulb ‘blows’).

How to join a bulb:

Circuit diagram Two bulbs joined end to end (in series) This is how christmas tree lights are joined together If one bulb is unscrewed the other bulb will also go out

Circuit diagram Two bulbs joined side by side (in parallel) This is how the lights in a house are wired together. If one bulb is unscrewed the other bulb will stay alight

Changing the brightness of a bulb 

Circuit diagram Two cells makes the bulb brighter because there is a higher voltage

Circuit diagram Two bulbs (in series) makes the bulbs dimmer because it is more diffcult for the electricity to flow

Making the wire longer will make the bulb dimmer

Circuit diagram Two cells and two bulbs is the same brightness as one cell and one bulb

Using a switch

Circuit diagram All the switch does is to break the circuit and switch everything off (or on) It does not matter where we put a switch in the circuit. A switch like this is sometimes called a SPST switch ( SPST=Single Pole Single Throw)

Sometimes a circuit does not work.

The three main causes for a circuit not working are:

• A wire not connected (or broken)
• The bulb 'blown'. This is when the filament has melted.
• The batteries are dead (flat)

There is something wrong with each of the circuits below. can you see what it is? (Hold your mouse over the diagram to find out)
source :http://www.mikecurtis.org.uk

Microorganisms

Micro-Organisms

Helpful micro-organisms     Harmful micro_organisms

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There is a group of living organisms that are so small we need a powerful microscope to see them.

They are called micro_organisms.

The main kinds of micro-organism are the bacteria, the fungus and a virus

Helpful micro-organisms: Bacteria and fungi in soil help dead leaves rot. The rotting leaves add food to the soil for plants to use. Bacteria are used to make yogurt and cheese. Yeast is used to make bread rise. Yeast is also used to make wine and beer.

Harmful micro-organisms: Bacteria and viruses can cause disease or illness. They spread very easily from one person to another. Bacteria in food can cause food poisoning. Uncovered food can go mouldy. Mould is a kind of fungus

and now in more detail........................

How micro-organisms can be helpful (friendly micro-organisms!)
	Inside the soil there are millions of bacteria and fungi. These bacteria and fungi feed on dead leaves and dead animals causing them break down (rot) and turn into simple chemicals. The rotting leaves mix with the soil and provide food for the plants and form a vital part of the food chain. Fact File Soil containing lots of rotting leaves is often called loam. Loam is dark in colour and crumbly. It is rich in food for plants Bacteria and fungi from the soil are sometimes called decomposers.
	Yogurt is made by adding special bacteria to milk. The milk is kept warm to help the bacteria multiply. The bacteria feed on sugars in the milk and make acid which helps the milk thicken. Fact File In most yogurt the bacteria are still alive when it is eaten. The bacteria in yogurt are good for your digestion Bacteria (and sometimes fungi) are also used to make cheese.
	When bread is made a micro-organism called yeast is added to the dough to make the bread rise. The yeast feeds on sugars in the dough and make a gas called called carbon dioxide. When the bread is cooked the yeast dies but the carbon dioxide gas stays in the bread and forms all the little bubbles that you see. Fact File Yeast is also used to make the alcohol in beer and wine. The carbon dioxide bubbles make the beer fizzy.

How micro-organisms can be harmful (nasty micro-organisms!)
	Some illnesses, like a sore throat or tummy upset are caused by bacteria. Other diseases, like chicken-pox, are spread by a tiny micro-organism called a virus. Viruses are even smaller than a bacteria They spread easily from one person to another. Fact File It is important to cover your mouth when sneezing and also to wash your hands after using the toilet to try and stop the spread of diseases. The water from some rivers (specially in hot countries) can contain bacteria and should not be drunk until after it has been boiled (which kills the bacteria)
	Raw chicken can contain a bacteria called salmonella. Salmonella causes food poisoning if you eat it Fact File It is important to cook chicken well to kill the salmonella. If you eat chicken that is not cooked properly some of the bacteria may get into your gut and make you very ill. Do not store raw food with cooked food as the salmonella can spread.
	Bread (and other foods) will go mouldy if you leave it open to the air. The mould is spread by tiny spores. It is best to keep the bread wrapped to keep the spores away from it. Fact File The mould appears as blue or white blotches. Mould is a kind of fungus

Some bacteria

	E.Coli bacteria These live inside your gut and are normally very useful as they help you digest your food
	Streptococci bacteria. The streptococcus causes a sore throat

Magnets

Magnets

Magnets are pieces of metal that attract iron

Different types of magnet

Bar magnet

Horseshoe magnet

Button magnet

Every magnet has two poles

N= North seeking pole

S= South seeking pole

The poles of a magnet is where the magnetic force is the strongest.

Iron filings sticking to thepoles of a horseshoe magnet

A magnet has lines of magnetic force around it

When we sprinkle iron filings on to a piece of paper laid over the magnet we can see the magnetic field lines For a demonstration click here

Rules about magnetic poles

Poles that are different (unlike poles) attract each other

Poles that are the same (like poles) repel (push) apart

Friction

Introduction

Friction is a force between two surfaces that are sliding, or trying to slide, across each other.

Friction always slows a moving object down. Air resistance is a type of friction.

This section includes:

• What is friction?
• Useful friction and reducing friction
• Air resistance
  
  

  What is friction?

  Friction is a force between two surfaces that are sliding, or trying to slide, across each other. For example when you try to push a book along the floor friction makes this difficult.
  Friction always works in the direction opposite from the direction the object is moving, or trying to move. Friction always slows a moving object down.

  More or less friction

  The amount of friction depends on the materials from which the two surfaces are made. The rougher the surface, the more friction is produced.
  For example, you would have to push a book harder to get it moving on a carpet than you would on a wooden floor. This is because there is more friction between the carpet and the book than there is between the wood and the book.

  Heat

  Friction also produces heat. For example, if you rub your hands together quickly, they get warmer.
  
  

  Useful friction and reducing friction

  Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tyres skidding on the road.
  Ice causes very little friction, which is why it is easy to slip over on an icy day. But this is a good thing for ice skating and sledging.

  Reducing friction

  Sometimes we want to reduce friction. For example we use oil to reduce the friction between the moving parts inside a car engine. The oil holds the surfaces apart, and can flow between them. The reduced friction means there is less wear on the metal, and less heat produced.
  
  

  Air resistance

  Air resistance is a type of friction between air and another material. When an aeroplane flies through the air, for example, air particles hit the aeroplane, making it more difficult for the aeroplane to move through the air.
  Some shapes, known as streamlined shapes, cause less air resistance than others. Aeroplanes and cars are streamlined, so that they move through the air as easily as possible.
  Source : BBC UK
  

  
  

Food Chains

Introduction

Food chains connect all organisms. If a creature's food source is changed in any way, the creature's life changes too.

You can see how the feeding relationships between animals, plants and humans work.

This section includes:

• Animals and plants are linked by Food Chains
• Producers and Consumers
• Prey and Predators
  
  
  Animals and plants are linked by food chains
  Animals get energy and nutrients by eating other animals or plants.
  For example
  • caterpillars eat leaves
  • small birds eat caterpillars
  • owls eat small birds
  • eagles eat owls
  These links between animals and plants are called food chains.
  Nearly all food chains start with a green plant.

  Changes to food chains

  If one part of a food chain alters, the whole food chain is affected. For example, if a disease suddenly wiped out caterpillars, it would affect owls, eagles and many other animals.
  Most animals and plants are part of more than one food chain.
  

  
  

  Producers and consumers

  Plants are called producers because they make their own food. They are at the start of a food chain.
  Animals are called consumers because they eat other plants and animals.

  
  

  Prey and predators

  A predator is an animal that eats other animals.
  The animals that predators eat are called prey.