Do you know what is gravity? To understand our physical world, gravity and 4 related terms i.e., gravitational acceleration, gravitational force, gravitational field, and gravitational field strength are the most fundamental and important concept in physics.

Introduction

Did you ever feel a mix of excitement and a little fear on a roller coaster or during the drop on a free–fall tower ride? Or perhaps you have swung high on a pendulum ride like a Pirate Ship or Looping Starship and experienced a brief moment of weightlessness.

All these thrilling sensations are linked to one powerful and ever–present force: gravity. If you notice, here we discuss three important terms of physics;

• free–fall
• weightlessness
• gravity

Gravity and 4 Related Terms

In this blog, we shall only discuss the science behind gravity.

What Is Gravity, Anyway?

Gravity is the phenomenon or effect that refers to the attraction between objects having definite mass. It is the phenomenon that causes objects to fall towards the Earth and planets to orbit around the Sun. In simple terms, gravity is the pulling agency.

How to Define Gravitational Acceleration?

It is defined as;

“the acceleration experienced by an object in free fall due to gravitational force within a gravitational field.”

Representation

It is represented by the symbol g.

Value of g

For objects near the surface of the Earth, the value of g is approximately 9.81 m/s² (~9.8 m/s² or 10 m/s²).

Note that;

• The value of g can vary slightly depending on altitude and location.
• The value of g shows that the velocity of a freely falling object increases by 9.8 m/s² for every second.

Gravitational Force

It is referred to the specific attractive force that exists between any two objects with mass. It is determined by Newton’s Law of Universal Gravitation.

It is the force that holds the universe together. Because of this force, not only we walk on the Earth but also the Moon orbits around the Earth. In simpler term, it is an invisible tether that pulls two objects.

It is the weakest of the four fundamental forces in nature. Despite its weakness, gravity has a long-range effect and dominates at astronomical scales. It influences the motion of planets, stars, and galaxies.

Origin of Gravitational Force

The mathematical models of force of gravitation describe its effects. As of today, we know that it arises due to mass and also how it behaves over large distances. However, its fundamental cause or origin—what gives rise to gravity—remains mysterious in the context of modern physics.

In essence, gravity is observed, but its fundamental nature (such as the possible existence of gravitons, hypothetical particles that mediate gravitational force) has not been confirmed.

What is a Gravitational Field?

It is defined as;

“a vector field that describes the gravitational force experienced per unit mass at any given point in space around a massive object.”

The strength and direction of the field at any location is determined by the mass creating the field and the distance from that mass. Basically, (imaginatively) it is like a giant invisible spider-web that is surrounding the Earth. Any object in this field will feel the tug of gravity.

Gravitational Fields in a Nutshell

• The closer we are to Earth, the stronger the pull (or force). That is why astronauts in space feel weightless, meaning a sensation of no weight.
• It always pulls things toward the centre of the Earth. So, if we dig a deep hole, gravity will still point downwards.

Gravitational Field Strength

It is defined as;

“the measure of the gravitational force experienced by a unit mass placed at a point in the gravitational field.”

In simple terms, it tells us how strong the gravity is at any location in the field.

Mathematical Formulation

It is given by the formula:

For a Test Mass

   

Where:

• g = gravitational field strength at a point
• Fg = gravitational force experienced by a test mass due to the Earth (or a massive object)
• m = test (object) mass

For a Source Mass

   

Where:

• G = gravitational constant
• M = gravitational field generating mass
• r = distance from the centre of the mass

Unit

In SI system of units, it is measured in newtons per kilogram (N/kg).

Type of Quantity

It is a derived quantity and vector in nature, meaning it has both magnitude and direction (toward the mass generating the field).

Near the Earth Surface

On the Earth surface, its strength is approximately 9.8 N/kg.

This means that for every kilogram of mass, the body experiences a gravitational force of 9.8 newtons. This value decreases as we move farther away from the Earth centre (as in space stations).

How Gravity Changes with Height?

Ever climbed a mountain and felt lighter (apart from being tired)? That is because, the farther we are from the Earth centre the gravity weakens. If we could climb super high, gravity would barely pull us!

Mathematical Formulation

   

OR

   

So, the higher we go, the gentler hug we shall get from the Earth.

How Does Gravity Change on Other Planets?

It does not remain the same everywhere, instead, its strength varies as per location or the body. On some planets, we would feel lighter as a feather; on others, we would feel like a ton of bricks!

• Moon: Around 1/6 g of the Earth
• Mars: Only 38% of the Earth g
• Jupiter: About 2.5 times stronger g than Earth

Conclusion

Gravity is a fundamental force that affects everything from the drop of a leaf to the orbits of planets. It pulls objects towards the Earth, shapes the universe, and gives us a sense of weight and stability.

While we experience its effects every day, the mystery of its true nature still captivates scientists. Whether through free-fall, weightlessness, or gravitational fields, it plays a crucial role in our understanding of the physical world.

Frequently Asked Questions (FAQs)

What is gravity?

It is the force of attraction between objects that have mass, causing them to pull towards each other.

What is gravitational acceleration?

It is the acceleration an object experiences when falling freely under the influence of gravity, approximately 9.8 m/s² near Earth’s surface.

What is free fall?

Free fall refers to the motion of an object solely under the influence of gravity, without any air resistance or other forces.

Why do astronauts feel weightless in space?

Astronauts feel weightless because they are in free fall, continuously falling towards Earth while in orbit, creating a sensation of weightlessness.

How does gravity change with height?

It weakens as we move further from the Earth surface because gravitational force decreases with distance from the Earth centre.

Is gravity the same on all planets?

No, it varies depending on the mass and size of a planet. For example, the Moon has weaker gravitational effect, and Jupiter has much stronger gravitational effect than Earth.

What is the gravitational constant (G)?

The gravitational constant (G) is a fundamental constant used in the calculation of force of gravity, with a value of approximately 6.674×10⁻¹¹ Nm²/kg².

What is a gravitational field?

Itis a region of space around a massive object where other objects experience a force of attraction due to gravity.

What happens to gravity in space?

In space, it is much weaker, but it still exists. Objects in space can experience microgravity, a very small gravitational pull.

What is the difference between weight and mass?

Mass is the amount of matter in an object, while weight is the force gravity exerts on that mass. Weight can change depending on the strength of gravity, but mass remains constant.