GCSEScienceAQACombined Science: SynergyPhysical SciencesRevision NotesInteractions Over Small & Large DistancesForces & Energy ChangesMass & Weight

Mass & Weight (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Exam code: 8465

Written by: Katie M

Updated on 5 March 2026

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Weight

Weight is defined as:

The force acting on an object due to gravitational attraction

Planets have strong gravitational fields
- So, they attract nearby masses with a strong gravitational force
Because of weight:
- Objects stay firmly on the ground
- Objects will always fall to the ground
- Satellites are kept in orbit

Diagram illustrating Earth, with a satellite orbiting and an object falling towards the surface, labelled "Falling Objects" and "Satellite". — **Some of the phenomena associated with gravitational attraction and the weight force**

Mass (kg) is related to the amount of matter in an object
Weight (N) is the gravitational force exerted on an object with mass
- The more mass an object has, the larger the weight force it will experience
Weight and mass are directly proportional
The size of the weight force depends on the gravitational field strength (g)

Measuring Weight

Mass is commonly measured using a top pan balance
- The weight can be found indirectly by calculation
Weight can be measured directly using a calibrated spring-balance, also known as a newton-meter
- This device is a type of weighing scale which measures force in Newtons
- It consists of a spring fixed at one end with a hook to attach an object at the other

Digital scales showing 100g and a spring balance reading 1 newton with labelled parts; illustrating the relationship between mass and weight. — **Weight can be measured indirectly using a top-pan balance or directly using a newton-meter**

Examiner Tips and Tricks

Mass and weight are not the same and this is one of the most common misconceptions in GCSE Physics.

Mass is a measure of how much matter there is in a substance or object. It is measured in kilograms (kg) and is a scalar quantity.
Weight is the force experienced by an object with mass in a gravitational field. It is measured in newtons (N) and is a vector quantity.

Avoid using the term 'gravity' in your exam because it can mean different things. Specify either gravitational force / weight or gravitational field strength / acceleration due to gravity.

Since mass is measured in kilograms, if a value is given in grams convert it to kg by dividing by 1000.

Calculating Weight

Weight, mass and gravitational field strength are related using the equation:

Equation W = mg with arrows pointing to "Weight (N)," "Mass (kg)," and "Acceleration due to gravity on Earth (9.81 N/kg or ms⁻²)."

g is known as the acceleration due to gravity or the gravitational field strength
- On Earth, g = 9.8 m/s² (or N/kg)

Weight on other planets

An object’s mass always remains the same
- However, its weight depends on the strength of the gravitational field on different planets
For example, the gravitational field strength on the Moon is 1.6 N/kg
- This means that an object’s weight will be about 6 times less than on Earth

Man standing on Earth and Moon, illustrating weight differences; 70 kg mass, 687 N weight on Earth, 114 N on Moon due to gravity variation. — **On the moon, your mass will stay the same but your weight will be much lower**

The value of g (gravitational field strength) varies from planet to planet depending on their mass and radius:

Diagram of gravity on celestial bodies: Sun 293.0, Jupiter 24.7, Saturn 10.5, Uranus 9.0, Earth 9.8, Mars 3.7, Moon 1.7 N/kg. — **Gravitational field strength of objects in our solar system**

Worked Example

A student estimates they would have a weight of 190 N on Mars.

The gravitational field strength on Earth is 9.8 N/kg.

The gravitational field strength on Mars is 3.8 N/kg.

Calculate the weight of the student on Earth.

Answer:

Step 1: List the known quantities

Weight on Mars, W_M = 190 N
Gravitational field strength on Mars, g_M = 3.8 N/kg
Gravitational field strength on Earth, g_E = 9.8 N/kg

Step 2: Write out the equation relating mass and weight and rearrange for mass

W = mg

Divide both sides by g:

$m = \frac{W}{g}$

Step 3: Calculate the student’s mass

The student’s mass is the same anywhere in the universe

$m = \frac{W_{M}}{g_{M}} = \frac{W_{E}}{g_{E}}$

$m = \frac{190}{3.8} = 50 kg$

Step 4: Calculate the student’s weight on Earth

W_E = m × g_E = 50 × 9.8 = 490 N

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