Physics C: Mechanics

Gravitation

# Gravitational Forces

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Gravitational Forces

Gravitational Forces

Key Terms

**Gravity**: A force of attraction between all mass, particularly evident between large bodies such as the Earth and Moon.**Mass**: The amount of matter in an object. Immune to changes in volume or density.**Weight**: The force of gravity acting on a mass. Changes with the strength of the gravitational field.**Gravitational field strength (g)**: The force of gravity per unit mass at a point in a gravitational field.

Newton's Law of Universal Gravitation

- Every object in the universe attracts every other object with a force directed along the line of centres for the two objects.
- This force is proportional to the product of the
**masses**of the two objects and inversely proportional to the square of the distance between the centres of the two objects. - The mathematical representation is:
**F = G(m1 * m2) / r^2****F**is the force of gravity (measured in newtons)**G**is the gravitational constant**m1**and**m2**are the masses of the objects**r**is the distance between the centres of the two objects

Gravitation and Weight

- An object’s weight refers to the force with which it is pulled toward the centre of the Earth due to gravity.
- The weight can be calculated using
**W = mg**, where:**W**is weight (measured in newtons)**m**is the mass of the object (measured in kilograms)**g**is the gravitational field strength (measured in N/kg)

- On Earth, g is approximately 9.81 N/kg. Therefore, an object with a mass of 1 kg has a weight of 9.81 N on Earth.

Gravitational Field Strength

- Gravitational field strength is the force of gravity per unit mass.
- It varies based on location, being strongest at the surface of an object and decreasing as you move further away.
- The formula to compute gravitational field strength is:
**g = F/m**, where:**g**is the gravitational field strength (measured in N/kg)**F**is the gravitational force (measured in newtons)**m**is the mass of the object experiencing the force (measured in kilograms)

Importance of Understanding Gravitational Forces

- Gravitational forces are fundamental to many aspects of everyday life and scientific study, from how objects fall to the ground to the prediction of planetary orbits.
- Understanding gravity and its effects can help solve real-world problems, such as the construction of buildings and bridges, and it also forms the basis for exploring other areas of physics, such as relativity.