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
In a point-model free-body diagram, each external force is drawn as a scaled arrow 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 measures a resultant from a force-addition drawing whose arrows have random lengths. Why is her measurement unreliable?
- Arrow lengths only show the time each force acts
- Arrow labels alone make every drawn length accurate
- Arrow lengths must follow the same force scale
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 · The common starting dot represents the object in a point model. Extended-body diagrams can preserve separate application points.
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.
Arrow lengths must follow the same force scale · Measuring a resultant needs a consistent force scale. Random arrow lengths do not preserve the forces' relative sizes.
5 N · At right angles the diagonal follows Pythagoras: 3, 4, 5.