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 → Motion ↓


Free fall and acceleration due to gravity


This topic revolves around two incredible concepts in physics: free fall and acceleration due to gravity. Imagine a ball falling from a tall building. What happens? Let's explore these fundamental ideas to understand the nature of motion when gravity is the primary influence.

Understanding free fall

Free fall is when an object is falling under the influence of gravity only. This means that there are no other forces acting on it, such as air resistance or friction. Visualizing free fall helps us understand how objects move in a gravitational field.

free fall

Suppose you are standing on a tall tower and are dropping a stone. Since only the force of gravity is acting on it, the stone is falling down freely. There is no other force making it fall down except the gravitational force of the earth.

How does gravity affect free fall?

Gravity is a force that pulls objects toward the center of the Earth. Near the Earth's surface, the acceleration due to gravity is about 9.8 m/s 2 This means that for every second that an object falls, its velocity increases by about 9.8 m/s.

Acceleration due to gravity, g = 9.8 m/s²

This is an important factor in free fall, as it indicates how fast an object will move downwards while falling.

Motion of freely falling objects

Let's consider how the velocity of a freely falling object changes over time. If you release an object from rest, its velocity after a certain time can be found using the following formula:

v = g * t

Where:

  • v is the final velocity in meters per second (m/s).
  • g is the acceleration due to gravity, 9.8 m/s².
  • t is the time the object has been falling in seconds.

For example, if an object falls freely from rest for 3 seconds, its velocity will be:

v = 9.8 m/s² * 3 s = 29.4 m/s

Therefore, after three seconds, the object is moving downward at a velocity of 29.4 m/s.

Distance covered during free fall

Calculating the distance travelled by an object during free fall is as important as finding its velocity. The formula for finding the distance travelled or displacement travelled by a freely falling object starting from rest is:

d = (1/2) * g * t²

Where:

  • d is the displacement in meters (m).
  • g is the acceleration due to gravity, 9.8 m/s².
  • t is the time in seconds.

Suppose an object is falling freely for 4 seconds, then we can calculate the distance covered by it as follows:

d = (1/2) * 9.8 m/s² * (4 s)² = 78.4 m

This result implies that the object fell a distance of 78.4 meters in 4 seconds.

Graphical interpretation

Graphically representing free fall and vibration due to gravity helps us understand the relationship between displacement, velocity and time.

Time Velocity V = G * T

In this graph, the red line shows the object's velocity over time, which increases linearly due to the constant acceleration of gravity.

Air resistance and real world effects

While free fall does not require air resistance, real-world scenarios are different. Air resistance, or drag, acts against gravity, slowing the acceleration of falling objects. Factors that affect air resistance include the object's speed, its surface area, and the density of the air.

For example, if a feather and a ball are dropped simultaneously they will experience different effects of air resistance, causing the feather to fall at a slower speed under normal atmospheric conditions.

Terminal velocity

Sometimes, objects falling through a fluid such as air or water reach a constant speed called terminal velocity. At this point, the force of air resistance is equal to the gravitational pull, resulting in a net force of zero, allowing the object to continue descending at a constant speed.

This concept is important for activities such as skydiving, where a skydiver achieves terminal velocity before deploying the parachute.

An experiment to demonstrate free fall

Performing a simple free-fall experiment improves understanding. Drop a small object such as a stone or piece of paper from a known height and measure the time it takes to reach the ground. Calculate the distance using the formula:

d = (1/2) * g * t²

Compare your experimental results to theoretical calculations. Consider the effects of air resistance and predict the deflection accordingly. Repeat the experiment with different falling objects and see how size and mass affect free fall.

Conclusion

Understanding free fall and acceleration due to gravity provides a solid foundation for understanding more complex motion concepts. These principles lay the groundwork for further study in mechanics and help explain many phenomena in the physical world. As you experiment and explore, remember that the simplicity of gravity is what makes it such a profound force, affecting countless phenomena in the universe.


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Free fall and acceleration due to gravity

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