Arrows that push and pull

Science · Forces & Motion · ages 14-15

Name ______________________ Date ____________

Which group lists only scalars?
- Distance, speed, mass
- Displacement, velocity, force
- Force, weight, speed
Which of these is a vector?
- Speed
- Force
- Mass
A free-body diagram shows one arrow per force, drawn to scale from the same dot.
Circle one: True False
Two teams pull a rope with equal opposite forces of 50 N. What is the resultant?
- 0 N
- 100 N
- 50 N
A sledge is pulled forward with 9 N while friction pulls back with 4 N. What is the resultant?
- 13 N forward
- 5 N backward
- 5 N forward
Forces add as plain numbers, so direction never matters.
Circle one: True False
Zoe reads a resultant off arrows drawn at random lengths. What is wrong?
- Nothing: arrow length never matters
- Free-body diagrams need no labels
- Arrows must be to scale, or the diagonal means nothing
One force of 3 N points east and another of 4 N points north. What is the size of the combined force?
- 7 N
- 5 N
- 12 N

Answer key

For grown-ups. Fold this page away before handing over the rest.

Distance, speed, mass · Distance, speed and mass all carry size only.
Force · Force carries a direction too, while speed and mass do not.
True · Isolate the object, then draw every force as a scaled, labelled arrow.
0 N · Equal opposite pulls cancel, leaving zero.
5 N forward · Allow for direction: 9 minus 4 leaves 5 N forward.
False · Forces add as vectors, and opposite pulls cancel.
Arrows must be to scale, or the diagonal means nothing · Unscaled arrows lie, so the reading cannot be trusted.
5 N · At right angles the diagonal follows Pythagoras: 3, 4, 5.