AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Students should be able to describe the interaction between pairs of…
Full specification wording
Contact and non-contact forces: Students should be able to describe the interaction between pairs of objects which produce a force on each object. The forces to be represented as vectors.
Forces arise from interactions between pairs of objects, and each object in the pair experiences a force.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 7 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Forces arise from interactions between pairs of objects, and each object in the pair experiences a force. In a contact interaction, such as a book resting on a table, the book pushes down on the table and the table pushes up on the book. In a non-contact interaction, such as two magnets or the Earth and a falling ball, the objects still exert equal and opposite forces on each other without touching. These paired forces act on different objects, so they do not cancel when you consider either object alone. Represent each force as a vector: an arrow whose length shows magnitude and whose head shows direction. When describing an interaction, name both objects, state the type of force, give its direction, and note that the two forces are equal in size and opposite in direction.
What earns the marks
- Identifies that forces come in pairs arising from an interaction between two objects.
- Names both objects in the interaction and states the force each exerts on the other.
- Classifies the interaction as contact or non-contact, with a suitable example such as friction or gravity.
- States that the two forces in the pair are equal in magnitude and opposite in direction.
- Represents each force as a vector arrow with length for magnitude and arrowhead for direction.
- Explains that the paired forces act on different objects, so they do not cancel each other out.
Common mistakes and how to put them right
Saying the two forces cancel because they are equal and opposite.
Put it right by noting they act on different objects, so each object feels only the force acting on it.
Describing only one force, such as the table pushing up on the book, and omitting the book pushing down on the table.
Put it right by naming both forces in the pair.
Drawing both force arrows on the same object pointing in opposite directions and treating them as balanced.
Put it right by placing each arrow on the object that experiences that force.
Exam tips
- Use the sentence pattern: object A exerts a force on object B, and object B exerts an equal and opposite force on object A.
- Label each vector arrow with the object it acts on, not just the type of force.
- For non-contact forces, state the field involved, such as gravitational, magnetic or electrostatic, to show the interaction is real.
Try the lesson
The start of the Contact and non-contact forces: Students should be able to describe the interaction between pairs of objects which produce a force on each object. The forces to be represented as vectors. lesson, made from checked teaching notes for this specification point.
Have a go first
A book rests on a table. Which statement describes the interaction between the book and the table?
Listen
Forces arise from interactions between pairs of objects, and each object in the pair experiences a force. In a contact interaction, such as a book resting on a table, the book pushes down on the table and the table pushes up on the book. In a non-contact interaction, such as two magnets or the Earth and a falling ball, the objects still exert equal and opposite forces on each other without touching. These paired forces act on different objects, so they do not cancel when you consider either object alone. Represent each force as a vector: an arrow whose length shows magnitude and whose head shows direction. When describing an interaction, name both objects, state the type of force, give its direction, and note that the two forces are equal in size and opposite in direction. A strong answer earns marks for these points. Identifies that forces come in pairs arising from an interaction between two objects. Names both objects in the interaction and states the force each exerts on the other. Classifies the interaction as contact or non-contact, with a suitable example such as friction or gravity. States that the two forces in the pair are equal in magnitude and opposite in direction. A common slip: Saying the two forces cancel because they are equal and opposite. Instead, noting they act on different objects, so each object feels only the force acting on it. Exam tip: Use the sentence pattern: object A exerts a force on object B, and object B exerts an equal and opposite force on object A.
See it
Key words
Say what each word means before you turn the card.
Contact interaction
Try answering aloud or in your head before turning the card.
Non-contact interaction
Try answering aloud or in your head before turning the card.
Vector
Try answering aloud or in your head before turning the card.
Paired forces
Try answering aloud or in your head before turning the card.
See every definition
- Contact interaction
- An interaction in which the objects touch, and each object in the pair experiences a force.
- Non-contact interaction
- An interaction in which the objects still exert equal and opposite forces on each other without touching.
- Vector
- An arrow whose length shows magnitude and whose head shows direction, used to represent each force.
- Paired forces
- Forces that are equal in size and opposite in direction, acting on different objects, so they do not cancel when either object is considered alone.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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