SUmmary
Unit one
Friction
We can observe friction force in many things like:
1- Friction between rubber ball and the ground.
2- Friction between the bicycle tyre and the ground.
The friction force has an effect in the opposite direction of the movement.
Friction occurs between two surfaces when one of them touches the other, the friction force is always in the opposite direction of the moving object.
Types of friction:
- One of the two surfaces is constant to the other. This force prevents the object from a sliding way on the wooden board while going up.
- When the cube slides down on the wooden board, it is affected by a less friction force. When the cube moves down, the direction of the friction force is upwards.
Friction force:
The amount of force that exists between two surfaces and affects the movement in the opposite direction.
Friction force changes due to the change of the material type of each surface.
Ex: The friction force of:
Glass and glass is lower than glass and metal.
Rubber and dry cement is greater than wet cement and rubber.
Friction disadvantages:
1- Damage of internal parts of machines.
2- Rise in the temperature of certain parts of machines.
Ways of decreasing the friction force:
1- Using lubricant and oil to form thin layer between the two surfaces to decrease friction.
2- Using ball bearing to be put between the surfaces of the machines in ternal moving parts like in cars and wheels.
Note:
Ball bearing consists of a group of metal balls with a smooth surface with almost no friction.
Friction applications
We can observe friction force in many things like:
1- Friction between rubber ball and the ground.
2- Friction between the bicycle tyre and the ground.
The friction force has an effect in the opposite direction of the movement.
Friction occurs between two surfaces when one of them touches the other, the friction force is always in the opposite direction of the moving object.
Types of friction:
- One of the two surfaces is constant to the other. This force prevents the object from a sliding way on the wooden board while going up.
- When the cube slides down on the wooden board, it is affected by a less friction force. When the cube moves down, the direction of the friction force is upwards.
Friction force:
The amount of force that exists between two surfaces and affects the movement in the opposite direction.
Friction force changes due to the change of the material type of each surface.
Ex: The friction force of:
Glass and glass is lower than glass and metal.
Rubber and dry cement is greater than wet cement and rubber.
Friction disadvantages:
1- Damage of internal parts of machines.
2- Rise in the temperature of certain parts of machines.
Ways of decreasing the friction force:
1- Using lubricant and oil to form thin layer between the two surfaces to decrease friction.
2- Using ball bearing to be put between the surfaces of the machines in ternal moving parts like in cars and wheels.
Note:
Ball bearing consists of a group of metal balls with a smooth surface with almost no friction.
Unit two
Circulatory System and Circulation
Excretion and human urinary system
Kinds of waste materials:
1- Carbon dioxide and water vapour.
2- Nitrogen wastes (uria and uric acid).
3- Excess salts.
Body should get rid of waste materials because the body can't use them and most of them are dangerous or poisonous.
How to get rid of waste materials:
1) Solid wastes stored in large intestine.
2) Carbon dioxide and water vapour get rid by lungs.
3) Excess salts by sweat from skin.
4) Nitrogen wastes removed by the kidneys.
Urinary system:
Its function to filter the blood of excess salts, urea, uric acid and other waste materials and expels them out in the urine.
Urinary system:
Located in abdomenal cavity near the back bone
Urinary system consists of:
1) The kidneys: Bean shaped organs exist at both sides. Function of the kidneys is filtering the blood from urine.
2) The ureters: Two narrow tubes that carry urine from the kidneys to the urinary bladder.
3) The urinary bladder: a balloon like a sac. That receives urine from the ureters – it temporary stores urine until it is released from the body to outside through the urethra.
Note:
The body gets rid of excess salts by secreting sweat from special glands in the skin which known as sweat glands.
How to maintain the urinary system healthy:
1) Drink appropriate amounts of water daily especially in summer.
2) Eat healthy and balanced food.
3) Avoid schistosomiasis disease (bloody urine).
4) Don't keep urine for long periods inside your body.
Unit three
Soil Components
- Soil has different colors.
- Soil contains many components (pieces of rocks, water, air and decayed materials (Humus)
- Humus is usually dark brown or black.
Soil:
The loose superficial layer of earth's crust, it is composed of minerals mixed with decayed materials and also contains different micro-organisms.
Importance of soil:
It is important for plants, animals and human life.
Plants grow in soil, giving food for animals and some animals take the soil as home.
The composition of soil: (gravel – mud – silt – humus)
How was Egypt's soil formed?
Breaking of rocks of Ethiopian plateau by water, wind, rains and heat then transfer by flood water to River Nile, then to the valley where it is deposited.
Soil and living organisms:
Many insects dig tunnels in the soil and animals add nutrients to soil and when they die they decompose to humus.
Leaves and other parts of plant decay to form humus.
Top soil layers contain roots and animals.
Rocky layers don't contain much humus.
Roots of plants help the soil to decrease soil erosion and add nutrients to the soil.
Earth worms dig tunnels in soil allowing air, water and nutrients to pass easily throughout the soil and it makes it easy for roots to grow.
Types and properties of soil
Soil can be classified into three different types |
||
Clay soil |
Sand soil |
Silt soil |
- Composed of clay, silt, small amount of sand and humus. It has black color. - It has small size particles It is hard compactness. It has poor areation and. high absorption of water. - Slow drainage of water. It is more holding of water It is fertile soil. |
- Composed of sand small amount of clay, silt and rare humus. It has yellow color. - Large particles size. Weak compactness. Good areation and low. absorption of water. - Fast drainage of water. Less holding of water. Less fertile soil. |
- Composed of mixtrue of gravel, clay, sand, silt and humus. It has grey color. - Medium size of particles. Medium compactness. Medium areation and medium absorption of water Medium drainage of water. - Medium holding of water. High fertile soil. |
Soil and plants:
1- Sand soil: Suitable for sweet potato, potato and peanut.
2- Clay soil: Cotton, rice, sugar cane, wheat and vegetables.
3- Silt soil: Many plants, strawberry, lemon, pomegranate and orange.
How can soil be protected from pollution?
Soil pollution:
Any change in the environment that disturbs the natural balance and harms its living organisms.
Soil pollutants:
- Materials that cause soil pollution
- Some agricultural soil pollutants:
1) Chemical pesticides: chemicals used to kill pests harm the soil and human health.
2) Chemical fertilizers: harm human and animals.
3) Industrial wastes: from factories and acid rains.
4) Increasing soil salinty: leads to dryness of soil cause loss of cultivated plants.
How to protect soil from pollution:
1) Rationalizing the use of pesticides and fertilizers and use natural ones.
2) Technology investment to treat water and build factories far from farmlands.
3) Irrigation of agricultural land regularly.
General Exams