Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Mechanics → Gravitational force ↓


Mass and weight


Understanding the concepts of mass and weight is very important in the study of physics, especially in the subject of gravity and mechanics. These two terms, often used interchangeably in everyday language, have different meanings and implications in the world of physics. Let us look at these differences and their relation to gravity in a structured manner.

What is mass?

Mass is one of the fundamental properties of an object. It is a measure of the amount of matter present in an object. The mass of an object is a scalar quantity, which means it has only magnitude and no direction. It is usually measured in kilograms (kg) in the International System of Units (SI).

Mass remains constant regardless of location. For example, if you have a book with a mass of 1 kilogram, it will have the same mass whether it is on Earth, on the Moon, or in the middle of interstellar space. The mass of an object is determined by the amount and type of atoms it contains.

Visual example: representation of mass

1 kg mass of the cube

What is the weight?

Weight, unlike mass, is a vector quantity. This means it has both magnitude and direction. Weight is the force exerted by gravity on an object. It depends on both the mass of the object and the acceleration due to gravity at the location where the object is present.

The formula to calculate the weight is:

Weight (W) = Mass (m) × Acceleration due to gravity (g)

The acceleration due to gravity on Earth is about 9.8 m/s². Therefore, an object with a mass of 1 kilogram will weigh about 9.8 Newtons on Earth.

Visual example: Representation of weights

9.8 N weight of one cube

Difference between mass and weight

  • Stability: Mass remains constant and does not change with location. Weight changes with the strength of the gravitational field.
  • Units: Mass is measured in kilograms (kg), while weight is measured in newtons (N).
  • Quantity type: Mass is a scalar quantity. Weight is a vector quantity, which means it has direction as well as magnitude (the direction is toward the center of gravitational pull).

Example to illustrate the difference

Imagine that you are standing in three different places: the Earth, the Moon, and a spacecraft in deep space.

On Earth:

- Your mass is 60 kg.
- Your weight is calculated as follows:

Weight = Mass × Acceleration due to gravity = 60 kg × 9.8 m/s² = 588 N

On the Moon:

- Your mass remains 60 kg.
- The acceleration due to gravity on the Moon is about 1.6 m/s².
- Your weight on the moon is:

Weight = 60 kg × 1.6 m/s² = 96 N

Deep space:

- Your mass is still 60 kg.
- Gravity is negligible in deep space, so you are nearly weightless.
- Your weight is approximately 0 N.

Understanding the role of gravity

Gravity is the natural force of attraction between any two masses. It gives weight to an object and affects the motion of celestial bodies. The stronger the gravitational field, the greater the weight of the object.

The strength of gravity depends on two factors:

  • The mass of objects. More mass means more gravity.
  • Distance between objects. Greater distance means weaker gravity.

The force of gravity can be calculated using Newton's law of universal gravitation:

F = G × (m₁ × m₂) / d²

Where F is the gravitational force, G is the gravitational constant, m₁ and m₂ are the masses, and d is the distance between the centers of the two masses.

Practical implications and examples

1. Sports and athletics

- Athletes should consider their weight when performing exercises or competitions that involve jumping or lifting weights, as weight affects the downward force they must overcome.

2. Space exploration

- Scientists must calculate weight changes for people and equipment traveling to space or other planets to ensure proper functionality and safety. For example, lunar rovers must be engineered to handle the reduced weight and gravity on the moon.

3. Engineering and architecture

Structures such as bridges need to bear their own weight and the additional force of gravity acting on the vehicles and pedestrians using them.

Key concepts review

  1. Mass is a measure of matter and remains constant regardless of location.
  2. Weight is the force due to gravity, which varies with the strength of the gravitational field.
  3. The weight is directed toward the gravity source, such as the center of the Earth.
  4. Mass is measured in kilograms, while weight is measured in newtons.
  5. The equation Weight = Mass × Acceleration due to gravity shows how weight depends on both mass and local gravity.

Understanding these fundamental concepts in physics can be very helpful in studying and explaining a wide range of natural and technological phenomena. This understanding paves the way for more complex topics in physics and other scientific explorations.


Grade 9 → 1.3.5


U
username
0%
completed in Grade 9

← Prev (1.3.4)
Free fall and weightlessness
Next (1.3.6) →
Variation of g with height and depth

Comments 



Mass and weight

https://www.physicsflow.com/g9/1.3.5?pfal=en