Example 1
Name two forces on a book at rest on a horizontal table.
Gravity acts downward and the table’s support force acts upward. Both act on the book.
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Year 7
Contact and non-contact forces
Name forces and represent their direction on a single object.
Method and worked examples
A force is a push or pull measured in newtons, N. Contact forces include support, friction, air resistance and tension. Gravity and magnetic force can act without objects touching. A force diagram shows forces acting on one named object; arrow direction gives direction, and arrow length can give magnitude using a stated scale.
A book resting on a table has downward gravitational force and upward support from the table. Friction acts against sliding relative to a surface. Motion is not itself a force, so do not label an arrow “motion”. To read a scaled arrow, multiply its length by the stated force per length. Several forces can act on an object simultaneously.
Example 1
Example 2
A force scale is 1cm=2N. What does a 3cm right-pointing arrow represent?
3×2=6N to the right.
Watch out: Motion is not an interaction. Forces can change motion, but an object can keep moving without a forward resultant force.