Mass, Weight and Gravitational field strength

All objects with mass have a gravitational field around them. A gravitational field is where a mass experiences a force.

  • all objects with matter have a gravitational field strength that attracts other objects

  • the greater the mass the greater the GFS(gravitational field strength) - moon and earth both have a GFS but earth is greater than the moon

  • Gravitational field strength gets weaker the farther you are from the planet’s center

Conversions:
The get the GFS of a object you do(gravity force = weight):

gravity force(N) / mass(kg) = GFS(N/kg)

Weight:

Weight is the force(gravity force) acting on an object due to the pull of gravity from a massive object like a planet

  • Weight and mass are directly proportional(BIGGER MASS = GREATER GRAVITY FORCE meaning for a given GFS the greater the mass the greater the weight

  • Weight is a non contact force so an object does not need to be on the surface to experience weight

  • Weight decrease the further you are from the center of the planet as GFS decreases

How to find out the weight of objects:

The Earth’s gravitational field strength (g) is 10 N/kg. This means that for each kg of mass, an object will experience 10 N of force.

This means the weight of object on earth is the mass of that object multiplied by 10N/kg e.g. weight of an apple = 0.1kg x 10N/kg= 1N

This means weight of object varies on different planets but mass stays the same

Uniform Gravitational Field

  • The field strength is the same everywhere.

  • The gravitational field lines are parallel and evenly spaced.

  • This is a good approximation near the Earth’s surface (or any large flat region).

📌 Example:

  • Standing on Earth's surface: gravity pulls everything straight down with about 9.8 N/kg

Radial Gravitational Field

  • The field spreads out in all directions from a central point.

  • The field lines are not parallel — they are radial, pointing toward the center.

  • Gravitational field strength decreases as you move further away

📌 Example:

  • Space around a planet or the Sun’s gravity pulling planets into orbit.