Rivision for primary 5

Friction force:
It is the force exists between two surfaces when they touch each other and it effects on the opposite direction of the movement.
**The disadvantage of friction:
The internal parts of machines are often damaged (due to a rise in their temperature) as a result of the friction force between their moving parts and money is wasted.

**Ways to decrease the friction force:-
1-Using lubricants and oil in car engine
They form a thin layer between the parts of machines

2-Using ball bearing it is formed of a group of small metallic balls exist in the axis of car engine to transmits the motion from car engine to the wheels.
The circulatory system:
It is the system that transported the digested food, oxygen gas and water to all the body cells and carries the wastes away from the body cells.
Help in maintaining your body healthy
The circulatory system consists of:
1-the Heart. 2-Bloodvessels. 3-Blood.
**[NOTE]
Atria receive blood from veins, while ventricles pump blood through arteries.
Arteries end with blood capillaries, while veins begin with blood capillaries
Minor blood circulation
The blood circulation between heart and lungs


Major blood circulationnu
Blood circulation between the heart and all body parts

minor blood circulation or pulmonary blood circulation
major blood circulation or systemic blood circulation