Gravitation is a natural force that pulls all objects in the universe toward one another. Every object that has mass attracts every other object. The Earth attracts objects toward its centre, which is why things fall downward when you drop them.

Gravitation helps us to stay on the ground, and it also helps us to keep the atmosphere around the Earth.

Gravitational force is the force of attraction between two masses.

1. The Earth attracts you.


2. You also attract the Earth, but the Earth’s mass is much larger, so its pull is stronger.

Earth’s gravitational pull gives weight to objects.

1. Objects fall toward the Earth: When you throw an object up, it comes down because gravitation pulls it.


2. It gives objects weight: Weight is the force with which gravity pulls an object toward the ground.


3. It keeps planets in orbit: The planets move around the Sun because the Sun’s gravity holds them.


4. It causes tides: The Moon’s gravity pulls on the Earth’s oceans and creates tides.


5. It controls the movement of satellites: Artificial satellites stay in orbit because of Earth's gravitational force.

These effects help us to understand how objects move in the world and in space.

This formula is used to calculate gravitational potential energy, which is the energy an object has because of its height above the ground.

Gravitational Potential Energy (Gr) = mass (m) × gravitational acceleration (g) × height (h)

1. m = mass in kilograms


2. g = gravitational acceleration ≈ 10 m/s²


3. h = height in metres

Example

A 2 kg stone is lifted 5 metres above the ground.

Gr = 2 × 10 × 5 = 100 joules

This means the stone has 100 joules of gravitational potential energy.

This calculation helps us to know the energy stored because of height.

Mass is the amount of matter that a body contains. It tells us how much substance is inside an object. Mass does not change because it does not depend on location or gravity. Whether you are on Earth, the Moon, or in space, your mass remains the same.

Weight is the force with which gravity pulls a body toward the centre of a planet. Weight depends on the strength of the gravitational pull. If gravity becomes stronger, weight increases. If gravity becomes weaker, weight decreases.

This relationship is expressed through the formula:

Weight (W) = mass (m) × gravitation (g)

Where:

1. m stands for mass measured in kilograms (kg).


2. g stands for gravitational acceleration. On Earth, this is approximately 10 m/s².


3. W stands for weight measured in newtons (N).

Weight changes because different places have different gravitational strength. For example:

1. A person will weigh less on the Moon because the Moon’s gravity is weaker.


2. The same person will weigh more on Jupiter because Jupiter’s gravity is stronger.


3. The mass of the person remains constant everywhere.

Examples

1. A boy with mass 40 kg on Earth will have a weight of: W = 40 × 10 = 400 N


2. The same boy on the Moon, where gravity is about one–sixth of Earth’s gravity, will have a weight of: W = 40 × (10 ÷ 6) ≈ 66.7 N


3. Even though the boy’s weight changed from 400 N to about 66.7 N, his mass remained 40 kg.

1. It helps us to calculate how much force is needed to lift objects.


2. It helps us to understand why objects behave differently in space.


3. It helps us to improve safety in transportation and engineering.


4. It helps us to measure objects correctly in science and industry.


5. It helps us to understand how gravity affects daily activities.

Weightlessness is a condition in which a person or an object does not feel the effect of gravitational pull. It occurs when the only force acting on the body is gravity, with no supporting force from the ground or any surface. This usually happens during free fall or when an object is moving in orbit around the Earth.

Under normal conditions on Earth, your weight is felt because the ground pushes upward against your body. This upward push is called the normal reaction force. In weightlessness, this upward force is absent, so the body feels no weight even though gravity is still acting.

Examples of Weightlessness:

1. Astronauts inside a spacecraft experience weightlessness because the spacecraft and their bodies fall toward Earth at the same speed. They appear to float since there is no upward push on their bodies.


2. Objects falling freely, such as in an elevator free fall, experience weightlessness because they fall at the same rate as gravity pulls them, so no support force acts on them.


3. Space scientists floating inside a space station experience weightlessness because the station is continuously falling around Earth while moving forward at high speed.

Astronauts do not float because gravity is absent. Gravity is still acting on them very strongly. They float because they and their spacecraft are constantly falling toward Earth while moving forward fast enough to stay in orbit. This creates a continuous free-fall condition.

Weightlessness is very useful in scientific research because it helps scientists to study how plants, materials, liquids, and the human body behave when normal gravity is not felt. This information helps us to improve space travel, medicine, and technology.

A satellite is any object that moves around a larger object in space due to gravitational attraction. Satellites follow a curved path called an orbit. Satellites can occur naturally or be made by humans.

1. Natural satellites: These are satellites that occur naturally in space. The Moon is the Earth's natural satellite because it orbits the Earth. Other planets also have natural satellites (moons). Natural satellites help to control tides, stabilize planets, and reflect sunlight.


2. Artificial satellites: These are man-made satellites that are launched into space using rockets. They are designed for specific purposes such as communication, weather monitoring, navigation, and scientific research. Artificial satellites remain in orbit because Earth's gravitational force pulls them inward while their forward speed keeps them from falling straight down.

Satellites stay in orbit due to a balance between two forces:

• The forward motion of the satellite.


• The gravitational pull of the Earth.

When these two forces balance, the satellite keeps circling the Earth.

• Communication: Satellites help in transmitting television signals, phone calls, and internet data across long distances.


• Weather forecasting: Meteorologists use satellites to observe cloud patterns, storms, and climate conditions.


• Navigation (GPS): Satellites help in tracking locations for cars, ships, airplanes, and mobile phones.


• Military and security: Satellites are used for surveillance, intelligence gathering, and national defense.


• Scientific research: Satellites help scientists study planets, stars, space conditions, and environmental changes on Earth.

Satellites play a major role in modern life. They help us to communicate, navigate, predict weather, study space, and improve technology. Without satellites, many services we use daily would not function.

Space travel involves sending astronauts and spacecraft outside the Earth’s atmosphere. To escape Earth’s gravity, a spacecraft must reach escape velocity, which is about 11.2 km/s.

It involves leaving the Earth’s atmosphere and moving into space where there is no air, no weather, and very little gravity compared to Earth.

For a spacecraft to move out of Earth, it must overcome the strong pull of gravity. This requires a very high speed known as escape velocity. The escape velocity of Earth is about 11.2 km/s, which means a spacecraft must travel at this speed to break free from Earth's gravitational force.

Gravity plays a very important role in every stage of space travel. It influences how rockets take off, how spacecraft move, and how they return to Earth.

1. Controlling how rockets lift off: Rockets must produce a force greater than Earth's gravitational pull to rise into space. They burn fuel rapidly to generate enough thrust (upward force) to overcome gravity.


2. Pulling spacecraft back to Earth: When a spacecraft loses speed or finishes its mission, Earth's gravity pulls it back. This is why spacecraft re-enter the atmosphere and come down with great speed. Parachutes or landing engines are used to slow them down safely.


3. Guiding the paths of space missions: Gravity influences how spacecraft move in space. Space scientists use gravity from Earth, the Moon, and other planets to change a spacecraft’s direction or speed. This technique is called gravity assist.

• Rockets carry large amounts of fuel that create powerful thrust.


• Spacecraft are designed to withstand the lack of air and extreme temperatures in space.


• Advanced navigation systems help astronauts and satellites follow correct orbits and paths.

Gravitation affects everything in space travel. By understanding how gravity works, engineers and scientists can:

1. Design rockets that can overcome Earth’s gravitational pull.


2. Calculate orbits for satellites and space stations.


3. Plan missions to the Moon, Mars, and other planets.


4. Ensure spacecraft land safely on Earth or other planets.


5. Use gravity assist to save fuel and travel longer distances.

Space travel has expanded human knowledge about the universe. It helps scientists to study planets, stars, galaxies, and space conditions. It also leads to new technologies that improve life on Earth.

1. It helps us to stay on Earth’s surface.


2. It helps us to walk, because friction works with gravity.


3. It helps us to pour water downward.


4. It helps us to make rain fall from the sky.


5. It helps us to control the movement of cars, balls, and other objects.


6. It helps us to make pendulums swing (useful in clocks).


7. It helps us to maintain the movement of ocean tides.

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Summary

1. Gravitation is the force that pulls objects toward one another.


2. Gravity gives weight, causes falling, and controls planetary motion.


3. The formula for gravitational potential energy is Gr = mgh.


4. Weightlessness occurs when gravitational pull is not felt.


5. Satellites depend on gravity to stay in orbit.


6. Gravity is important for everyday activities and space exploration.