AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Forces and elasticity: force, F, in newtons, N
Force is a vector quantity measured in newtons (N).
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 7 of 19
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Force is a vector quantity measured in newtons (N). In the context of elasticity, the force F usually refers to the load or tension applied to a spring or elastic object, or the restoring force it exerts. One newton is the force needed to give a 1 kg mass an acceleration of 1 m/s². When a spring is stretched, the extension depends on the applied force, and the relationship is described by Hooke's law: F = k × e, where k is the spring constant and e is the extension.
What earns the marks
- States that force is measured in newtons (N) and is a vector quantity with both magnitude and direction.
- Identifies F in F = k × e as the force applied to, or exerted by, the elastic object, measured in newtons.
- Uses the equation F = k × e correctly, substituting values with consistent units before calculating.
- Distinguishes between the applied force and the weight of a suspended mass, using W = m × g where g is gravitational field strength.
- Reads force values from a force–extension graph, recognising that the gradient gives the spring constant in the linear region.
Common mistakes and how to put them right
Writing force in kilograms or grams instead of newtons.
Put it right: Mass is measured in kg, but force is measured in N and calculated using W = m × g.
Forgetting to convert extension from centimetres to metres before using F = k × e.
Put it right: Convert to SI units so that k in N/m and e in m give F in N.
Treating force as a scalar and ignoring its direction.
Put it right: Force is a vector, so state the direction, such as the downward force of a weight or the upward tension in a spring.
Exam tips
- Always write the unit N after a calculated force and check that the value is reasonable for the context.
- Show the equation, substitution and answer clearly so that method marks can be awarded even if the final value is wrong.
- When a mass is given, calculate the force using W = m × g before substituting into F = k × e, and state g = 9.8 N/kg unless told otherwise.
Try the lesson
The start of the Forces and elasticity: force, F, in newtons, N lesson, made from checked teaching notes for this specification point.
Have a go first
A spring is stretched by a force of 12 N. What is the unit of this force?
Listen
Force is a vector quantity measured in newtons (N). In the context of elasticity, the force F usually refers to the load or tension applied to a spring or elastic object, or the restoring force it exerts. One newton is the force needed to give a 1 kg mass an acceleration of 1 m/s². When a spring is stretched, the extension depends on the applied force, and the relationship is described by Hooke's law: F = k × e, where k is the spring constant and e is the extension. A strong answer earns marks for these points. States that force is measured in newtons (N) and is a vector quantity with both magnitude and direction. Identifies F in F = k × e as the force applied to, or exerted by, the elastic object, measured in newtons. Uses the equation F = k × e correctly, substituting values with consistent units before calculating. Distinguishes between the applied force and the weight of a suspended mass, using W = m × g where g is gravitational field strength. A common slip: Writing force in kilograms or grams instead of newtons. Instead, mass is measured in kg, but force is measured in N and calculated using W = m × g. Exam tip: Always write the unit N after a calculated force and check that the value is reasonable for the context.
Key words
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Force
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Hooke's law
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Newton
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Weight
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See every definition
- Force
- A vector quantity measured in newtons (N) with both magnitude and direction.
- Hooke's law
- The relationship F = k × e, where k is the spring constant and e is the extension.
- Newton
- The force needed to give a 1 kg mass an acceleration of 1 m/s².
- Weight
- Calculated using W = m × g, where g is gravitational field strength, and distinguished from the applied force.
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