What is Gravity and How to Measure Gravity?

Gravity is the force exerted by Earth or other planets to pull an object towards their surface.

The acceleration due to gravity on Earth's surface is g = 9.8 meters per each squaresecond.

In physics, g stands for the acceleration due to gravity, and its standard value on Earth is 9.8 m/s². 

This means that when an object is falling freely, its speed increases by 9.8 meters per second (every single second), ignoring air resistance. 

This value forms the foundation for many important concepts in classical mechanics, a branch of physics that studies how objects move and the forces affecting their movement.

Here are some of those fields where the formula for 'g' is used: 

1) Gravitational Field Calculations: 

It is often written as 9.8 m/s² (meters per second squared) or 9.8 N/kg (Newtons per kilogram) when referring to gravitational field strength. 

• Newton is the force needed to accelerate a one-kilogram mass at the rate of one meter per second squared.
• It is expressed as N = 1 kg x 9.8 (m/per Second Squared) = 9.8 Newtons per 1kg of mass. So, the force needed to throw a 1kg mass is 9.8 Newtons.
• The name Newton was chosen to honour Sir Isaac Newton, who established the Three Laws of Motion.

2) Weight Calculation: 

You can calculate the gravitational force (weight) of any object by multiplying its mass by g, using the formula w= mg. 

3) Calculation of Motion in a Vacuum: 

In kinematics, equations for falling objects use g to determine how fast they drop or how high they can travel against Earth's pull.

Approximation of g:

Although the standard value is 9.81 m/s², the commonly used approximation in many physics textbooks and classroom problems is 9.8 m per square second.

Why is Gravity mentioned in Square Seconds?

Gravity is measured in "square seconds" because it describes an acceleration, which is the rate at which speed changes over time.

 

Acceleration measures the change in an object's speed in meters per second over each second.

 

When you write this out as a fraction, it looks like this:

Acceleration = (Change in Speed)\Time = Meters\Second\Second (where change in speed is measured in meters and time in seconds)

In mathematics, dividing a fraction by a variable multiplies the denominators together:

So, it becomes m per second squared.

But in Real Life,

A "square second" does not exist as a physical shape like a square foot of land. 

Instead, it is an abbreviation of "per second, per second."

If you drop a rock from a cliff, Earth's gravity accelerates it at roughly 9.8 m per second each second:

• At 0 seconds: The rock is stationary
• After 1 second: The rock falls at 9.8m/s
• After 2 seconds: The rock falls at the rate of 19.6 meters per second
• After 3 seconds: The rock falls at the speed of 29.4 meters, and so on

The speed increases at the rate of 9.8 m/s for each extra second that passes.

Does it mean that speed increases every second? 

Or does it mean that high-altitude objects fall at greater speeds than low-altitude objects?

It does not mean that gravity is higher at higher altitudes.

It means that speed increases every second while an object falls to the ground.

As long as an object is dropping, gravity continuously adds more speed to it. 

High-altitude objects hit the ground at much higher speeds because they have a longer distance to fall, giving gravity more time (seconds) to accelerate their speed.

• A rock dropped from a 5-meter roof falls for about 1 second and hits the ground at 9.8 m/s
• A rock dropped from a 45-meter cliff falls for about 3 seconds and hits the ground at 29.4 m/s. 

The cliff-rock drops faster at impact because gravity had 2 extra seconds to build up its speed, not because gravity itself was stronger up high.

A Twist in the Story?

In actual physics, Earth's gravity decreases as an object's altitude increases because of the greater distance from the center of the Earth.

• At sea level, g is about 9.81m/per suare second
• At the top of Mount Everest, g drops to about 9.77 meters per second squared.

An object starting at a high altitude actually accelerates a tiny bit slower at first. However, because it has so much time to fall and accumulate speed, it still hits the ground much faster than an object dropped from a lower altitude.

References:

https://byjus.com/physics/value-of-g/

https://www.vedantu.com/jee-main/si-unit-of-acceleration-due-to-gravity-physics-question-answer

https://study.com](https://study.com/academy/lesson/newtons-laws-and-weight-mass-gravity.html

https://www.sciencebuddies.org/stem-activities/speedy-science-how-does-constant-acceleration-affect-distances-traveled