AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    The weight of an object depends on the gravitational field strength at the…

    Full specification wording

    Gravity: The weight of an object depends on the gravitational field strength at the point where the object is.

    The weight of an object is calculated using W = m × g, where m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram (N/kg).

    Checked against the AQA 8464 specification (opens in a new tab) on .

    • Point 2 of 11
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    The weight of an object is calculated using W = m × g, where m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram (N/kg). Because g varies from place to place, the same object can have different weights in different locations. For example, g is about 9.8 N/kg on Earth, about 1.6 N/kg on the Moon, and about 24.8 N/kg on Jupiter. A 10 kg mass therefore weighs about 98 N on Earth, about 16 N on the Moon, and about 248 N on Jupiter. The mass stays 10 kg everywhere, but the weight changes because g changes. This shows that weight depends on the gravitational field strength at the point where the object is, while mass does not depend on location.

    What earns the marks

    • Weight is calculated using W = m × g, where m is mass in kg and g is gravitational field strength in N/kg.
    • Gravitational field strength g varies with location, so the weight of an object can change from place to place.
    • Mass is the amount of matter in an object and does not change with location.
    • On the Moon, g is smaller than on Earth, so an object weighs less on the Moon even though its mass is unchanged.
    • On Jupiter, g is larger than on Earth, so an object weighs more on Jupiter even though its mass is unchanged.
    • When comparing weights in different places, use the same mass and the appropriate value of g for each place.

    Common mistakes and how to put them right

    • Thinking mass changes with location.

      Put it right: State that mass stays the same and weight changes.

    • Using the wrong value of g for a location.

      Put it right: Learn typical values such as Earth 9.8 N/kg, Moon 1.6 N/kg.

    • Forgetting to convert mass to kilograms before using W = m × g.

      Put it right: Check that mass is in kg.

    Exam tips

    • When a question gives a different value of g, use that value in W = m × g rather than automatically using 9.8 N/kg.
    • If asked to compare weights on Earth and the Moon, calculate both weights using the same mass and the correct g for each place.
    • Show your working clearly: write the equation, substitute the values, and give the unit N with your answer.

    Try the lesson

    The start of the Gravity: The weight of an object depends on the gravitational field strength at the point where the object is. lesson, made from checked teaching notes for this specification point.

    Have a go first

    An astronaut travels from Earth to the Moon. The gravitational field strength on the Moon is less than on Earth. What happens to the astronaut's mass and weight?

    Listen

    The weight of an object is calculated using W = m × g, where m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram (N/kg). Because g varies from place to place, the same object can have different weights in different locations. For example, g is about 9.8 N/kg on Earth, about 1.6 N/kg on the Moon, and about 24.8 N/kg on Jupiter. A 10 kg mass therefore weighs about 98 N on Earth, about 16 N on the Moon, and about 248 N on Jupiter. The mass stays 10 kg everywhere, but the weight changes because g changes. This shows that weight depends on the gravitational field strength at the point where the object is, while mass does not depend on location. A strong answer earns marks for these points. Weight is calculated using W = m × g, where m is mass in kg and g is gravitational field strength in N/kg. Gravitational field strength g varies with location, so the weight of an object can change from place to place. Mass is the amount of matter in an object and does not change with location. On the Moon, g is smaller than on Earth, so an object weighs less on the Moon even though its mass is unchanged. A common slip: Thinking mass changes with location: mass is constant, but weight changes because g changes. Instead, state that mass stays the same and weight changes. Exam tip: When a question gives a different value of g, use that value in W = m × g rather than automatically using 9.8 N/kg.

    See it

    A flowchart. At the top, a box reads 'Same object, mass m in kg' and an arrow leads down to 'Weight W = m × g'. From this box three arrows branch out to 'g on Earth about 9.8 N/kg', 'g on the Moon about 1.6 N/kg' and 'g on Jupiter about 24.8 N/kg'. Each of these leads to a further box: 'Weight on Earth', 'Weight on the Moon' and 'Weight on Jupiter' respectively. All three of these boxes lead to a final box reading 'Mass stays the same, weight changes because g changes'.
    It shows that the same mass gives different weights depending on the gravitational field strength at each location.

    Key words

    Say what each word means before you turn the card.

    Weight

    Try answering aloud or in your head before turning the card.

    Mass

    Try answering aloud or in your head before turning the card.

    Gravitational field strength

    Try answering aloud or in your head before turning the card.

    W = m × g

    Try answering aloud or in your head before turning the card.

    See every definition
    Weight
    Calculated using W = m × g, where m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram.
    Mass
    The amount of matter in an object, which does not depend on location and stays the same everywhere.
    Gravitational field strength
    A quantity measured in newtons per kilogram that varies from place to place, so the same object can have different weights in different locations.
    W = m × g
    The equation used to calculate weight, in which m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A flowchart. At the top, a box reads 'Same object, mass m in kg' and an arrow leads down to 'Weight W = m × g'. From this box three arrows branch out to 'g on Earth about 9.8 N/kg', 'g on the Moon about 1.6 N/kg' and 'g on Jupiter about 24.8 N/kg'. Each of these leads to a further box: 'Weight on Earth', 'Weight on the Moon' and 'Weight on Jupiter' respectively. All three of these boxes lead to a final box reading 'Mass stays the same, weight changes because g changes'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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