<h1><strong>CALCULATION OF GRAVITATIONAL FORCE</strong></h1> CONTENT <ol> <li>Definition of Gravitational Force</li> <li>Calculation of Gravitational Forces</li> </ol>   <h2><strong>Definition of Gravitational Force</strong></h2> This is the force with which the earth pulls all objects towards its centre. It is also called force of gravity. The instrument used for measuring gravitational force is called spring balance. <h2><strong>Calculation of Gravitational Forces</strong></h2> The unit of force is Newton (the symbol is N). The unit was named after Sir Isaac Newton who first discovered the facts about gravity. The weight of a body is the force the earth exerts on it. <strong>All forces are measured in Newton.</strong> On the earth surface the universal value of acceleration due to gravity (g) is 9.8m/s² or 10m/s² To calculate gravitational force (Gf). The following formulae are used: 1. F = mg, used for calculation of gravitational force. <strong>Example 1:</strong> Calculate the gravitational force required to pull down a mango fruit of 10kg falling with acceleration of 5m/s². <strong>Solution:</strong> F = mg, where F is unknown, m = 10kg, a = 5m/s² ∴ F = 10 × 5 = 50 N. <strong>Example 2:</strong>

<h1><strong>FRICTION: BALANCED AND UNBALANCED FORCES </strong></h1> CONTENT <ol> <li>Meaning of Friction</li> <li>Uses and Advantages of Friction</li> <li>Disadvantages of Friction</li> <li>How to Reduce Friction</li> <li>How to Reduce Friction</li> <li>Balanced and Unbalanced Forces</li> </ol>   <h2><strong>Meaning of Friction</strong></h2> The force that tries to stop a body from moving is called friction. Friction also means force that opposes motion. Friction can be reduced by lubrication i.e. adding oil and grease placed between the two surfaces in contact. The oil and grease are called lubricants. <h2 style="text-align: center;"><img class="size-full wp-image-36570 aligncenter" src="https://classhall.com/wp-content/uploads/2018/06/protection-from-friction.jpg" alt="Friction; Balanced and Unbalanced Forces - Protection from friction" width="396" height="239" /><strong>Protection from Friction</strong></h2> <span style="color: #008000;">Friction is a force that occurs when one object moves against another. The ceramic tiles on the outside of the space shuttle protect it from the great friction caused when the shuttle re-enters Earth’s atmosphere.</span> <h2><strong>Uses and Advantages of Friction</strong></h2> The following are the uses and advantages of friction:

<h1><strong>GRAVITATION AND WEIGHTLESSNESS</strong></h1> CONTENT <ol> <li>Meaning of Gravitation</li> <li>Effect of Gravitation on Objects</li> <li>Weightlessness</li> </ol>   <h2><strong>Meaning of Gravitation</strong></h2> Gravitation is a type of force that acts on a body across a distance, without any contact between the source and the body. The earth exerts a gravitational force on bodies by which it pulls these bodies towards its centre. This is why fruits fall to the ground from the tree and do not rise upwards. Also, when a stone is thrown upwards it soon stops its upward movement and starts to fall back to the earth. The force of gravity is a universal force. It exists between the earth and bodies and between planets and stars. <strong>Gravitational pull determines the weight of objects.</strong> The amount of force with which gravity pulls an object depends on three things, namely:

<h1><strong>THE EARTH IN SPACE</strong></h1> CONTENT <ol> <li>The Solar System</li> <li>The Eight Planets</li> <li>Earth's Rotation and Revolution</li> <li>Eclipse of the Sun and the Moon</li> </ol>   <h2><strong>The Solar System</strong></h2> The planet earth, on which we live, is moving through space all the time. It is going round the sun. In doing this it carries us all through space. The earth travels through the space but we do not realize this because the air around the earth is carried along with it. The sun together with all the bodies which revolves round it makes up the solar system. The solar system consists of the sun, eight planets and their moons along with dwarf planets, comets and asteroids which revolve round the sun. The solar system is divided into inner and outer parts. The inner part contains the Sun, Mercury, Venus, Earth and Mars while the outer part contains Jupiter, Saturn, Uranus and Neptune. The two parts are demarcated by asteroid belt.

<h1><strong>SPACE TRAVEL </strong></h1> CONTENT <ol> <li>Meaning of Space Travel</li> <li>Purpose/Advantages of Space Travel</li> <li>Dangers of Space Travel</li> </ol> <p style="text-align: center;"><img class="size-full wp-image-36596 aligncenter" src="https://classhall.com/wp-content/uploads/2018/06/space-travel-Yuri-Gagarin.jpg" alt="Space Travel - Yuri Gagarin" width="218" height="194" /><strong>Yuri Gagarin</strong></p> <span style="color: #008000;">On April 12, 1961, the Russian cosmonaut Yuri Gagarin blasted into orbit. He was the first person in space and completed an orbit of the Earth before landing. This photograph was taken just before lift-off.</span> <h2><strong>Meaning of Space Travel</strong></h2> Space travel is traveling from the earth to outer space. Space is the environment surrounding the earth, moon and other planets. Human beings are able to go to space and spend days and months using a space rocket called space shuttle. Space travels are expensive to run. <p style="text-align: left;">On 21st July, 1969 Neil Armstrong an American was the first person to step on the moon. He was followed by Edwin Aldrin, also 2 other Americans, Eugene Cernan and Harrison Schmitt who stayed for about 74 hours and 59 minutes on the moon surface. <img class="size-full wp-image-36597 aligncenter" src="https://classhall.com/wp-content/uploads/2018/06/space-travel.jpg" alt="Space travel" width="303" height="215" /><strong>Space Travel</strong></p> <span style="color: #008000;">For hundreds of years, people dreamed about traveling to outer space. The invention of huge rockets made space travel a reality. An astronaut first went into space in 1961 (A Russian, Major Yuri Gagarin). Only eight years later, astronauts landed on the Moon. Since then, people have continued to explore space.</span> <p style="text-align: center;"><img class="size-full wp-image-36598 aligncenter" src="https://classhall.com/wp-content/uploads/2018/06/rocketing-to-space.jpg" alt="Space travel - Rocketing to space" width="297" height="306" /><strong>Rocketing to Space</strong></p>

<h1><strong>SATELLITES</strong></h1> CONTENT <ol> <li>Meaning of Satellite</li> <li>Types of Satellites</li> <li>Uses of Satellites</li> </ol>   <h2><strong>Meaning of Satellite </strong></h2> A satellite is a natural body that revolves round the earth or another planet. As we have learned earlier, the earth has one satellite which is the moon. Scientist have launched artificial satellites (like space shuttle, rockets etc) into space to carry out experiments, collect information and learn more about other space. <h2><strong>Types of Satellites</strong></h2> The types of satellites include the following: <ol> <li>Communications satellites</li> <li>Weather satellites</li> <li>Navigation satellites</li> <li>Surveillance satellites</li> <li>Scientific satellites</li> </ol> <img class="size-full wp-image-36602 aligncenter" src="https://classhall.com/wp-content/uploads/2018/06/communications-satellite.jpg" alt="Satellites - Types of Satellites - Communications Satellites" width="320" height="195" /> <h3><strong>Communications Satellites</strong></h3>

<h1><strong>MEANING AND TYPES OF FORCE</strong></h1> CONTENT <ol> <li>Definition of Force</li> <li>Mathematical Expression of Force</li> <li>Types of Forces</li> <li>Differences between Gravitational Force and Magnetic Force</li> <li>Uses of Force</li> </ol>   <h2><strong>Definition of Force</strong></h2> Force is any action that moves an object or alters its uniform motion in a given direction. Force is the product of mass of the objects and its acceleration. The greater the mass of the object, the greater the force required to move it. Examples of force are pull, push, tension forces and frictional force between surfaces. <strong>Force is measured in Newton.</strong> <h2><strong>Mathematical Expression of Force</strong></h2> F ά mass × acceleration F = ma, where m = mass and a = acceleration due to gravity <h2><strong>Types of Forces </strong></h2> There are two types of force. These are; <ol> <li>Contact force</li> <li>Non-contact force/force field</li> </ol> <h3><strong>Contact Force </strong></h3>