4.5.1.3 Gravity

Spec reference: 4.5.1 (subtopic).

What you need to know

• Gravity
• Gravity is the natural phenomenon by which any object with mass or energy is drawn together.
• • The mass of an object is a scalar measure of how much matter the object is made up of. Mass is measured in kilograms (kg).
• • The weight of an object is a vector measure of how gravity is acting on the mass. Weight is measured in newtons (N).
• weight (N) = mass (kg) × gravitational field strength (N/kg)
• (The gravitational field strength will be given for any calculations. On earth, it is approximately 9.8N/kg).
• An object’s centre of mass is the point at which the weight of the object is considered to be acting. It does not necessarily occur at the
• centre of the object.

Self-assessment (checklist)

• I can describe what weight is.
• I can describe what affects the force of gravity close to
• I can describe what affects the weight of an object.
• I can recall and apply the correct equation to calculate
• I can rearrange the equation linking gravitational field
• I can describe where the weight of an object can be
• I can describe how the weight and mass of an object
• I can name the piece of equipment used to measure

Key steps (method)

• Identify what the question is testing and use the correct equation/definition.
• Show substitutions and units clearly.

Common mistakes

• Unit conversions, rearranging errors, or quoting a law without applying it.