What is Gravity?

Gravity is an invisible force that attracts objects towards each other. This becomes very noticeable when dealing with large bodies of mass, such as planets. This is because the greater the object’s mass is, the greater the gravitational force. Gravitational forces pull inward, towards the object’s centre. This is why on Earth, we are pulled towards the ground.

All planets, including Earth, in our solar system orbit the Sun, while the Moon orbits Earth. This happens due to the force of gravity.

A simplified representation of the Earth and the Moon. The Earth is shown in blue with green continents, and around it are three smaller illustrations: a tree with a red house behind it, the Leaning Tower of Pisa leaning. Circling the Earth is an orbit path on which the Moon, represented by a yellow circle labelled "Moon", is travelling, indicated by an arrow showing its direction around the Earth. The overall theme playfully incorporates elements from folklore and real-world landmarks to illustrate gravitational influence.

Gravitational Pull

All objects have mass, which changes only when you add or remove mass. However, weight does change because it’s a force that depends on gravity.

As seen in the example below on the left, when on Earth, the elevator falls due to gravity. This happens because it is within Earth’s gravitational pull. In space, a person becomes weightless and floats because they are outside Earth’s gravitational pull. Therefore, he is no longer drawn towards Earth’s centre.

On the left, there's a diagram of an elevator containing a stick figure. Above the elevator, text reads "The elevator falls due to gravity." Red arrows pointing downwards, labelled "Gravity", indicate the force pulling the elevator towards the "Ground" shown at the bottom. On the right side of the image, there's a depiction of Earth surrounded by a dashed orbit. A camera, with a stick figure floating away from it, is shown in the space outside the Earth, suggesting the effects of gravity in space. The overall theme illustrateS the concept of gravity both on Earth and in outer space.

Air Resistance

When an object falls towards Earth, it gets faster due to the force of gravity. The rate at which an object falls to the ground depends on how much air resistance there is.

In this case, the opposing force is air resistance, an upward force of friction that aims to slow the object down. Air resistance opposes gravity. Air resistance increases when the surface area of the object increases.

However, objects fall differently depending on how gravity and air resistance interact. For example, if you dropped an apple and a feather at the same time:

Feathers float and take longer to reach the ground, while an apple falls straight down. This is because there is much greater air resistance when the feather is falling compared to the apple.

The apple can fall through the air at a faster rate. This is based on Galileo’s discovery that objects with greater density (or more mass) will fall faster than less dense objects (or those with less mass) due to air resistance.

The difference in the movement of objects in different mediums. On the left, labelled "IN AIR", a feather and an apple are depicted. A solid blue arrow points downwards above the feather, indicating its slower descent, while a dashed orange arrow points directly to the apple, representing its quicker fall. On the right, labelled "IN A VACUUM", the feather and the apple are shown again. This time, both have solid blue and orange arrows respectively, indicating they fall at the same rate in the absence of air resistance. The overall image demonstrates the concept that in a vacuum, without air resistance, different objects fall at the same rate.

When a feather and an apple are dropped at the same time, air resistance causes the feather to drop fall more slowly than the apple. However, in a vacuum (such as space), where there is no air resistance, the apple and the feather would fall at the same rate and reach the ground at the same time.

You’ve used 0 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up