Science 7–10 · Year 7
How magnetic pull falls off with distance: paperclips through card spacers
Physical sciences — Forces, content group Magnets in everyday life (NSW Stage 4 focus area; ACARA places magnetic forces in Year 4, AC9S4U03, and has no Year 7 to 10 content description on magnetism, so only Year 7 inquiry codes are cited)
The idea
A magnetic force acts without contact and weakens quickly as the gap between magnet and object grows.
What you need
- bar or ceramic disc magnet, 1
- steel paperclips (small, 28 mm), 50
- thin card squares 1 mm thick, 20
- digital vernier callipers or ruler, 1
- 0 to 1 N and 0 to 5 N newton meters and a steel washer on a thread, 1 each (extension)
How to do it
- Hold the magnet's pole directly against a pile of paperclips, lift, and count how many clips it lifts in a chain or clump. Repeat three times and average.
- Place one card square (1 mm) on the pole face and repeat the count with the card between magnet and clips.
- Increase the card thickness one square at a time up to 10 mm, counting the clips lifted at each thickness, three trials each.
- Plot the average number of clips against gap thickness in millimetres and describe the shape of the curve.
- Extension: lay the magnet pole up with a stack of card squares on it, rest the steel washer on the card, and pull the washer straight up with the newton meter, recording the reading as it breaks away. Repeat for 0, 2, 4, 6, 8 and 10 mm of card, using the 0 to 5 N meter at small gaps and the 0 to 1 N meter once the reading falls below 1 N.
What you should see
The clip count drops steeply over the first few millimetres of card and keeps falling with each added millimetre; the plotted curve falls quickly then flattens rather than dropping in a straight line. The gap at which no clips are lifted depends on the magnet. The newton-meter extension shows the same shape: the pull-off force at 10 mm is a small fraction of the force at contact. The three trials at each gap scatter by a few clips, which is why averages are used.
What changes
- What you change
- gap between magnet and clips (mm of card)
- What you measure
- number of clips lifted (or pull-off force in N)
- What you keep the same
- same magnet and pole face
- same clips
- lift speed and technique
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- The magnet's pull is the same at any distance until it suddenly stops.
- Card or paper stops magnetism.
- A larger magnet always has a stronger pull.
Safety card
Hazards
- pinched skin between strong magnets
- small parts
Controls
- use one magnet at a time
- keep magnets away from phones and bank cards
Note
No hazardous chemicals or naked flames are used. Complete the school's risk assessment for the activity before the lesson; the NSW Department of Education Science safety and compliance page points to CSIS 1.7 (Risk assessment – a pre-requisite for risk control) for how to carry it out.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science 7–10 Syllabus (2023)SC4-FOR-01SC4-WS-04SC4-WS-05SC4-WS-06
- Australian Curriculum v9AC9S7I02AC9S7I04AC9S7I05AC9S7I06
Sources
The pages the author read to write this activity.