Science 7–10 · Year 7
Friction: force needed to slide a loaded wooden slider on different surfaces
Physical sciences — Forces (NSW Stage 4 focus area)
This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.
The idea
The friction force between two surfaces depends on the materials and on how hard the surfaces press together, not on the area in contact.
What you need
- wooden slider with a hook, about 200 g, 1
- 0 to 5 N newton meter, 1
- slotted masses, 100 g x 4
- test surfaces: bench top, sandpaper sheet (P80), smooth plastic sheet, carpet tile, 1 each
- electronic balance, 1
How to do it
- Weigh the slider. Place it on the bench top and hook the newton meter to it.
- Pull horizontally and slowly, watching the reading. Record the steady reading while the slider moves at constant speed; this is the friction force. Take three trials and average.
- Add 100 g, 200 g, 300 g and 400 g on top of the slider and repeat, so the slider presses harder on the surface while the surfaces stay the same.
- Work out the weight pressing down for each load (slider plus load, mass x 9.8 N/kg), plot friction force (N) against it (N) and describe the pattern.
- Keep the load fixed at 200 g and change the surface: sandpaper, plastic, carpet. Record the steady sliding reading for each.
- Turn the slider onto its narrow side with the same load and check whether the friction force changes.
What you should see
Friction rises in proportion to the weight pressing down, so the graph is a straight line through the origin and doubling the load on a surface doubles the pull needed. For example, if the friction on a surface is 0.3 times the weight pressing down, the 0.200 kg slider with 0.400 kg of load (5.88 N pressing down) needs a steady pull of 1.76 N, within the 0 to 5 N meter's range. The readings differ from surface to surface, which shows that the materials matter, and turning the slider on edge with the same load changes the reading little because the contact area does not set the friction force.
What changes
- What you change
- load on the slider (the weight pressing down) or the surface material
- What you measure
- friction force read on the newton meter (N)
- What you keep the same
- pull horizontal and steady
- same slider face for the load series
- same surface for the load series
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Friction depends on the area of contact.
- Friction only acts when something is moving.
- A smoother surface always means less friction.
Safety card
Hazards
- masses falling from the slider
Controls
- stack masses centrally
- work along the bench, away from the edge
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-06
- Australian Curriculum v9AC9S7U04AC9S7I02AC9S7I05AC9S7I06
Sources
The pages the author read to write this activity.