Just a little help to prepare your Science Test

What are forces?
Forces are ations which make objects move or change shape.

How many different forces have we studied?
There are different types of forces:
• Gravity: Gravity makes objects fall to the ground. Gravity attracts objects.
• Electric force: It makes electrical circuits work. It can attract or repe.
• Magnetic force: magnets and certain metals have magnetic force. It can attract or repel.
• Friction: friction is a contact force. It can slow or stop moving an object.

How can forces affect a moving object?
Forces can affect a moving object in different ways:
• Making an object move.
• Stop a moving object.
• Changing the direction of a moving object.
• Increasing the speed of an object.
• Reducing the speed of an object.

What is a machine?
A machine is an object that uses the action of a force or transforms one type of energy into another.

How can we classify machines?
We can classify machines
• According to the number of pieces that make them up.
o Simple machines: they are made up by a simple machine.
o Complex machines: they are made up by more than one simple machines.
• According to how they work.
o Some machines need human energy to work.
o Some machines need wind or water to work.
o Some machines need fuel to work.
o Some machines need electricity to work.
• Acroding to what they do.
o Machines which produce movement: these machines transform energy into movement.
o Thermal machines: these machines transform energy into heat or cold.
o Information-processing machines: they process information. We use them to communicate and to make calculations.

Which parts make up a machine?
• The casing and structure.
o The casing is the outer part of a machine. It protects it from dust, moisture and damages.
o The structure is the frame that supports the weight of the machine.
• Operating parts and mechanisms.
o The operating parts are all the parts that make up the machine.
o A mechanism is a group of operating parts that work together fo perform a special function.
• Engines and motors: they are the parts of a machine that produce movement.
• Electrical circuits and electronics.