FORCE

FORCE is a push or pull
forces acting on the body caused:

1. The body at rest become moving
2. The moving body to be at rest
3. The shape and size of the body change
4. The direction of the body can change

Force acting on a body, can be grouped into two kinds :

• Contact forces : force that results from direct touchFor example: muscular force, attraction force, spring force, frictional force
• Non contact force : force occurred without the touchFor examples: magnetic force, gravitational force, electric force

The force is a vector quantity because its has magnitude/ value and direction. International system (MKS) the unit of force is Newton ( N ). In CGS system unit is dyne

RESULTANT FORCE

1. if two or more forces in the same direction :     R = F1 + F2
2. if the two forces are in opposite direction, R = F1 – F2

EXAMPLES

1. A box on the floor is pushed by Amir to the right of 200 N and by Ali to the left of 200 N. What is the force resultant?
2. Two children push a cupboard, the child A pushes of force 20 N and the child B pushes of force 30 N. What is the force acting on the cupboard? ( floor is slippery)

FRICTION FORCE
Friction force is the force due to friction of two bodies surface
Direction of friction force is always against the direction of the bodies motion.

Beneficial frictional force
a. Frictional force between feet with the surface of floor
b. Car tires which is made serrated,
c. Braking system,
d. Parachute with the air.
Harmful frictional force:
a. The base of sandal become thin.
b. The air with the body of the motorcycle rider.

Frictional force is divided into two kinds:
Static frictional force: frictional force between two bodies that will start to move or at rest
Kinetic frictional force: frictional force between two bodies which one of the body moves
WEIGHT
Weight of the body is earth gravitational force acting on the body.
Mathematically:

W = m . g
With:
w = weight ( N )
m = mass ( kg )
g = gravitational acceleration ( m/s2 )

STATE OF MATTER

Matter is defined as everything which has mass, occupies space, and is convertible to energy. The phase of matters are solid, liquid and gas.

Characteristics of the solids :

1. Its shape is constant.
2. Its volume is constant
3. The location of particles are very close and have uniform composition
4. Inter particular attraction force is very strong
5. The movement of particles is not free, they only vibrate in their place

Characteristics of the liquids:

EXPANSION

OBJECTIVES

1. To do an expansion experiment on solid, liquid, and gas.
2. To explain the advantages of expansion in the daily life.

Do you know……..

1. why in a hot day roads can be damaged,
2. why a gap is given between rail roads,
3. and why bridge connectors are given a space?

HEAT

The heat energy is the total energy of particles composing a matter.
Before you discuss heat, it is better for you to understand first the definition of heat energy.

The Definition of Heat
What will happen if you touch a cool wall with your hands for several minutes? Your hand will feel cooler and the parts of the wall that you touch will be warmer. The temperature of your hand decreases while the temperature of the wall increases.The heat energy flows from your warm hand to the cool wall.