Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Mechanics ↓


Gravitational force


Gravity is a force that acts between any two objects with mass. It is an invisible force that pulls objects toward each other. It is the force that keeps us standing on Earth, enables the Moon to orbit around the Earth, and enables the planets to revolve around the Sun.

History of gravitation

The concept of gravity has been studied for centuries. One of the most famous scientists to work on gravity was Sir Isaac Newton. He formulated the law of universal gravitation in the late 17th century. The story goes that Newton was sitting under an apple tree when an apple fell on his head, leading him to wonder why objects fall toward the Earth. His curiosity about this phenomenon led him to develop the theory that all objects in the universe exert a gravitational force on each other.

Newton's law of universal gravitation

Newton's law of universal gravitation explains how this force works. This law says that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Its formula is:

F = G * (m1 * m2) / r^2

Where:

  • F is the gravitational force between the two objects (in newtons).
  • G is the gravitational constant, which is approximately equal to 6.674 × 10^-11 N m^2/kg^2.
  • m1 and m2 are the masses (in kilograms) of the two objects.
  • r is the distance (in meters) between the centers of the two masses.

A simple example

Imagine you have two small balls in space. If one ball has a mass of 2 kg and the other has a mass of 3 kg, which are 1 meter apart, you can calculate the gravitational force between them.

m1 = 2 kg
m2 = 3 kg
r = 1 m
F = G * (2 kg * 3 kg) / (1 m)^2 = 6G

This result tells us that the force between these two balls is six times the gravitational constant G

Importance of gravitational force

The force of gravity is something we experience in our everyday lives, even if we can't always see it directly. Here are some examples of how gravity is important:

  • It keeps the planets revolving around the Sun.
  • This causes objects to fall towards the earth when they fall.
  • It holds the gases in the Sun and other stars, causing them to form.
  • This affects the tides in the Earth's oceans.

Gravitational field

The gravitational field is the region of space around an object in which the other object will experience the force of gravitational attraction. The strength of the gravitational field is measured in newtons per kilogram (N/kg), and is often called the acceleration due to gravity.

The average gravitational field strength on Earth is about 9.8 N/kg. This means that for every kilogram of mass, the gravitational force is 9.8 newtons.

Visual example: gravitational field

Imagine a massive object like the Earth. A smaller object like a satellite moves toward the Earth. The arrows below show the gravitational force acting on the satellite as it gets closer.

Earth's mass | V
-------> -------> -------> Satellite

As the satellite approaches the Earth, the gravitational force increases, pulling it towards the planet.

Weight and mass

Weight is the force exerted by a gravitational field on an object. It is important to distinguish between weight and mass. Mass is the amount of matter contained in an object and is measured in kilograms. Weight, on the other hand, is the gravitational force acting on that mass.

The weight can be calculated using this formula:

Weight = Mass * g

Where g is the acceleration due to gravity.

Example of calculating weight

If your mass is 50 kg and you are standing on the Earth, your weight can be calculated as follows:

Mass = 50 kg
g = 9.8 N/kg
Weight = 50 kg * 9.8 N/kg = 490 N

So, a person with a mass of 50 kilograms exerts a force of 490 newtons towards the Earth.

Understanding classes

An orbit is a curved path that a celestial body, such as a planet or moon, takes around another body due to the force of gravity. Orbits are typically elliptical, meaning they have an oval shape.

Planets revolve around the Sun, and moons revolve around planets, because there is a gravitational pull between these bodies. This is why the Earth continues to revolve around the Sun and does not drift off into space.

Visual example: classrooms

Here is a depiction of the Earth revolving around the Sun:

Sun | V
*
/ 
/ 
| Earth
 /
 / *

The path taken by the Earth is elliptical, that is why the Earth is sometimes closer to the Sun and sometimes farther.

Gravity on other planets

The force of gravity varies on different planets and celestial bodies. This difference is due to the mass and radius of the planet. For example, the gravity on Mars is about 3.7 m/ s2, which is much weaker than Earth's gravity.

This difference in gravity would mean that an object would weigh less on Mars than on Earth, even if its mass remained unchanged.

Escape velocity

Escape velocity is the speed an object must reach to break free from the gravitational pull of another object. It is important in space travel. The formula to calculate escape velocity is:

v = √(2 * G * M / r)

Where:

  • v is the escape velocity.
  • G is the gravitational constant.
  • M is the mass of the celestial body (such as a planet).
  • r is the radius of the celestial body.

Example calculation of escape velocity

For the Earth, we can use the following values to find its escape velocity:

G = 6.674 × 10^-11 N m^2/kg^2
M = 5.972 × 10^24 kg (mass of Earth)
r = 6.371 × 10^6 m (radius of Earth)
v = √(2 * 6.674 × 10^-11 * 5.972 × 10^24 / 6.371 × 10^6)
v ≈ 11,186 m/s

This means that any object would have to travel at a speed of about 11,186 metres per second to escape Earth's gravity.

Conclusion

Gravity is essential to understanding how objects in space and on Earth interact. From holding galaxies together to determining how heavy an object feels, gravity is one of the fundamental forces that shape our universe. It affects not only the motion of planets and moons, but also the structure of the universe.


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Gravitational force

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