Gravitational Forces

❖  Gravity is the force of attraction between all objects that have mass. It determines the motion of the planets around the Sun, as well as the force of mutual attraction between two objects and between all cosmic bodies in the Universe, from the smallest particles to the largest galaxies.

Earth’s gravity is the force that keeps us firmly planted on the ground, it is the reason objects fall when we drop them.

Gravity is everywhere. It is intangible. We cannot see it. It is a force of attraction that exists between objects and the Earth. It acts in the water, on land and in the air.

❖  The gravitational field is a physical model of the invisible web around any body with mass. It explains the effect that one body exerts in space to create a force on another body.

Gravitational field strength is the force with which the gravitational field attracts a unit mass (mass of 1 kg). It is measured in newtons per kilogram – N/kg.

❖  Gravitational acceleration affects the magnitude of the gravitational force with which one body attracts another body. Therefore, on each planet, bodies fall at different accelerations — that is, they reach different speeds and travel different paths in the same amount of time.

❖  Isaac Newton’s Law of Universal Attraction, known as the Law of Gravitation, describes mathematically the relationship between the force of gravitational attraction, the masses of bodies, and the distance between them.

❖  The mass and weight of a body are two different but related concepts. Mass (m) is the amount of matter in a body. Weight is a measure of the gravitational force acting on an object.

According to Newton’s second law, weight is proportional to the mass of the body and the acceleration of free fall (g) and is expressed by the formula G = m.g

This means that the greater the mass of a body, the greater its weight at a given acceleration of free fall. The same body will have the same mass on the Moon and Earth but will weigh less on the Moon than on Earth because the gravity (g) on the Moon is weaker than on Earth.