Unit one

                    Friction

                    Friction applications

Unit two

                    Circulatory System and Circulation

                    Excretion and human urinary system

Unit three

                    Soil Components

                    Types and properties of soil

                    How can soil be protected from pollution?

General Exams

                    Exam One

                    Exam Two

                    Exam Three

                    Exam Four

                    Exam Five

Q uestion one: Complete the following:

1- The friction force can be observed between ……… and ……… .

bicycle tyre – ground  

2 - The friction force affects in ……… direction of ……… .

opposite – movement  

3 - The ……… force exists between two forces.

friction  

4 - When the cube slides down on the wooden board, the friction force is ……… .

small  

5 - The friction force between two surfaces made of glass is ……… than friction between glass and metal.

smaller  

6 - The friction causes ……… for parts of machines.

damage  

7 - The temperature rises inside machines is due to ……… .

friction  

8 - Friction forces can be decreased by using ……… and ……… .

lubricants – oil  

9 - Technicians use ……… to decrease friction in wheels.

ball bearing  

1 0- The smooth surface of balls in ball bearing makes the friction force ……… .

almost non-exits  

Q uestion two: Give reasons for:

1- The rubber ball stops after time on moving on the ground.

Due to friction force.  

2 - The friction force decreases the speed.

Because it affects in opposite direction of movement.  

3 - The internal parts of machines are damaged.

Due to friction force.  

4 - Some machines become hot on using them.

Due to friction force.  

5 - Using of lubricants and oil in some machines.

To decrease the friction force.  

6 - The friction between balls in ball bearing is almost non exist.

Due to their smooth surfaces.  

7 - The friction forces are not constant.

Because they change by change of the material of surface.

Q uestion three: What is meant by:

1- Friction force:

The force that affects in opposite direction of movement.

2 - Ball bearing:

Group of balls exists between two surfaces to decrease friction.  

Q uestion four:

Write two disadvantages of friction force.

1- Damage of internal parts of machines. 2- Temperature rise of machines.  

Q uestion five:

Write two methods to decrease friction force.

1-  Using lubricants and oil. 2- Using ball bearing.  

Q uestion six:

Explain why we need to push bicycle tyres to move.

Because there is a friction force between tyres and the ground.