Forces arise when two objects interact; the force on one object is always equal in size, and opposite in direction to the force on the other object; force arrows indicate the size, direction and location of each force.
Observable learning outcome:
Represent the size and direction of a force with an appropriate force arrow.
Correctly position a force arrow to show how a particular force acts.
Response, practical - to practise using an idea
Force, Newton, force meter, Newton meter, force-arrow
Terry et al (1985) found that many 11-14 year old students were quite ad hoc in their use of force arrows: they did not effectively start them from the point of action, use them to indicate the direction of force or change their length to indicate the size of the force. This may contribute, as Driver et al (1994) noted, to the difficulty that some students have in thinking of forces in terms of their magnitude and direction.
Drawing force-arrows to scale or interpreting relative sizes of forces from their lengths requires mathematical skills that some students will find difficult and which are not necessarily taught in mathematics lessons until age 12-13 (Boohan, 2016).
Measuring forces using force-meters and newton balances gives students experience of what different sizes of force feel like, and the opportunity to practise drawing accurate force arrows onto diagrams. Experiencing the forces first hand can help students understand how the size and position of a force-arrow represents a real force.
This practical activity gives students the opportunity to practise measuring forces and applying their understanding of force arrows, and to clarify their thinking through discussion. To support this, students should complete the practical in pairs or small groups.
Listening to individual groups as they work often highlights any difficulties they might have. These can often be overcome, through a whole class clarification or redirection part way through the activity. Two boxes on the student sheet have been left blank for the students to put in their own measurements.
Using the recording sheets can help some students organise their observations so they can more easily focus on the science. If some students are working with a teaching assistant, then a list of prompt questions for the TA could help to make this activity more purposeful. Some students may benefit from being challenged to plan and organise their own record keeping.
You may choose to use just 0-10 N force meters, or to give your students a choice of force-meter so they can measure a wider range of forces. This may require them to use a different scale for their force-arrows (other than 1cm = 1N).
For each student/pair/group:
- Force-meter (0-10N)
- Spring (Hooke’s law spring)
- 300g hanging masses
- Access to string
For the class:
- Balance(s) that read in Newton
- Newton meters for measuring different ranges of force
Balances need to be set to read in Newton. One 300g hanging mass per balance is needed.
String may be necessary to make loops to attach the force meter to objects.
Health and safety
Hooke’s law springs can deform and flick into eyes if they are significantly over stretched. If this is a possibility with your class you should consider using safety glasses.
Students may select to measure forces that involve heavy objects that can fall, or opening of doors that can trap fingers.
Practical work should be carried out in accordance with local health and safety requirements, guidance from manufacturers and suppliers, and guidance available from CLEAPSS.
|Mu pinali tõstmiseks vaja minev jõud.|
|Mu pinali mööda lauda lohistamiseks kuluv jõud.|
|Vedru 10 cm võrra pikemaks venitamise jõud.|
|Jõud, millega mõjub 300 g raskus maapinnale.|
|Jõud, mis ...|
|Jõud, mis ...|
Boohan, R. (2016) The language of mathematics in science, Association for Science Education, Hatfield, England.
Driver, R., Squires, A., Rushworth, P. and Wood-Robinson, V. (1994) Making sense of secondary science, research into children’s ideas, Routledge, London, England.
Terry, C., Jones, G. and Hurford, W. (1985) ‘Children’s conceptual understanding for force and equilibrium’, Physics Education 20(4): 162-5.