Why Is the Acceleration Due to Gravity 9.8 m/s²?
Gravity is one of the most important concepts in physics and explains why objects are pulled toward each other. It is a fundamental force that governs the motion of everything in the universe, from falling objects on Earth to the paths of planets and stars.
Understanding gravity helps you explain daily experiences, solve real-world physics problems, and build a strong foundation for further studies in mechanics and astronomy.
What is Gravity?
Gravity is the force of attraction that acts between all objects with mass. The more mass an object has, the stronger its gravitational pull.
For example, Earth has a large mass, so it pulls objects toward its center—this is why things fall down and why our atmosphere is held in place. Gravity also keeps the planets in orbit around the Sun and the Moon in orbit around Earth.
To read further about scientific explanations, see Gravitation and Universal Law of Gravitation.
Gravity Formula and Universal Law
The Universal Law of Gravitation states that every object attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
The formula is:
F = G × (m₁ × m₂) / r²
Where:
- F is the gravitational force in Newtons (N)
- G is the gravitational constant (6.674 × 10-11 N·m²/kg²)
- m₁ and m₂ are the masses (kg) of the two objects
- r is the distance (m) between the centers of the two masses
Acceleration Due to Gravity (g)
On Earth, the acceleration due to gravity is generally considered to be 9.8 m/s². This means that, if there were no air resistance, any object dropped from rest would increase its speed by 9.8 meters per second every second as it falls.
The value of 'g' can slightly vary depending on location (e.g., at poles or equator) and height above or below Earth’s surface.
For details on variations, refer to Gravity on Earth.
Difference Between Gravity, Gravitation, Mass, and Weight
| Gravity | Gravitation | Mass | Weight |
|---|---|---|---|
| Force attracting objects toward Earth | Attraction between any two masses | Amount of matter in a body | Force of gravity acting on mass |
| Always toward Earth's center | Acts between all objects everywhere | Constant, measured in kg | Varies with location (N) |
To explore more about these differences, see Difference Between Gravitation and Gravity and Difference Between Mass and Weight.
Stepwise Approach: Solving a Free Fall Problem
| Step | Description | Example |
|---|---|---|
| 1 | List known values (height, g, initial velocity) | h = 20 m, g = 9.8 m/s², u = 0 |
| 2 | Select proper kinematic equation | v² = u² + 2gh |
| 3 | Substitute values | v² = 0 + 2×9.8×20 = 392 |
| 4 | Solve for velocity | v = √392 ≈ 19.8 m/s |
For more examples and practice, check Gravitational Force and Escape Velocity.
Key Gravity Formulas
| Formula | Description | Unit |
|---|---|---|
| F = G(m₁m₂) / r² | Gravitational force between two objects | Newton (N) |
| g = 9.8 m/s² | Acceleration due to gravity near Earth's surface | m/s² |
| Weight = m × g | Relation between mass and weight | Newton (N) |
For further explanations, visit Value of Gravitational Constant and Centre of Gravity.
Applications and Examples of Gravity
- Gravity keeps us anchored to the Earth and holds the atmosphere in place.
- It is responsible for the orbits of planets, moons, and artificial satellites.
- The tides in oceans are caused mainly by the gravitational pull of the Moon.
- When a ball is thrown up, gravity pulls it down, causing it to fall back.
To see how gravity is studied with orbits, read Orbit Astronomy.
Next Steps for Deeper Learning
Ready to master more Physics topics?
Explore these linked resources for comprehensive notes and practice:
- Gravitation: Complete Concepts
- Centre of Gravity
- Escape Velocity and Orbital Motion
- Mass and Weight Explained
FAQs on Gravity in Physics: Concept, Laws and Formula
1. What is a simple definition of gravity?
Gravity is the force of attraction that pulls objects towards each other, especially toward the center of the Earth.
Key points:
- Acts on all objects with mass
- Responsible for keeping us on the ground
- Explains why things fall when dropped
2. What is the value of acceleration due to gravity (g) on Earth?
The standard value of acceleration due to gravity (g) on Earth is 9.8 m/s².
Highlights:
- It indicates that velocity increases by 9.8 m/s every second during free fall
- This value can slightly vary from 9.78 to 9.83 m/s² depending on location
3. What is the universal law of gravitation?
The universal law of gravitation states that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Formula: F = G × (m₁ × m₂) / r²
- F = Gravitational force
- G = Universal gravitational constant (6.674 × 10-11 N·m²/kg²)
- m₁, m₂ = Masses of objects
- r = Distance between centers
4. Who discovered gravity?
Sir Isaac Newton is credited with discovering the law of gravity in the 17th century.
Key facts:
- He formulated the universal law of gravitation in 1687
- His work explains the force that causes bodies to attract each other
5. Is gravity 9.8 everywhere on Earth?
No, gravity is not exactly 9.8 m/s² everywhere on Earth.
Variations occur due to:
- Latitude (greater at poles, less at equator)
- Altitude (decreases at higher elevations)
- Local geology and depth
6. What is the difference between gravity and gravitation?
Gravity refers specifically to the attractive force by which the Earth pulls objects towards its center. Gravitation is the general force of attraction between any two masses in the universe.
Summary Table:
- Gravity: Attraction towards Earth’s center
- Gravitation: Attraction between any two masses
7. What is the formula for gravitational force?
The formula for gravitational force is:
F = G × (m₁ × m₂) / r²
- F = gravitational force
- G = universal gravitational constant
- m₁, m₂ = masses involved
- r = distance between the masses
8. What is the difference between mass and weight?
Mass is the amount of matter in an object and remains constant everywhere. Weight is the force with which gravity pulls that mass towards Earth.
Key points:
- Mass (kg) does not change with location
- Weight (N) = Mass × Acceleration due to gravity (g), so it varies with g
9. Why does the value of g change with altitude and latitude?
The value of g changes because Earth's shape is not a perfect sphere and its mass distribution varies.
Factors:
- g is slightly higher at the poles than at the equator (due to Earth's flattening)
- g decreases as you move to higher altitudes above Earth’s surface
10. What are common misconceptions about gravity?
Common misconceptions include:
- Gravity is always exactly 9.8 m/s² (it varies by location)
- Gravity is the same as mass or weight (they are different concepts)
- Gravity only acts on heavy objects (it acts on all objects with mass)
11. Give one example of an everyday effect of gravity.
Gravity causes objects to fall towards the ground when released.
Examples:
- When you drop a ball, it accelerates towards the floor due to gravity
- Gravity keeps us, air, and the oceans anchored to Earth
12. How do you calculate the final velocity of a free-falling object?
Use the equation: v² = u² + 2gh
Steps:
- Set u = 0 (if starting from rest)
- g = 9.8 m/s²
- h = height of fall
- Calculate v = √(2gh)
