P2.3 Forces in action
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P2.3 Forces in action
Mathematical learning outcomes:
PM2.3i recall and apply: force exerted by a spring (N) = extension (m) x spring constant(N/m)
PM2.3ii apply: energy transferred in stretching (J)= 0.5 x spring constant (N/m) x (extension(m))2
PM2.3iii recall and apply: gravity force (N) = mass (kg) x gravitational field strength, g (N/kg)
PM2.3iv recall and apply: (in a gravity field:) potential energy (J) = mass (kg)x height (m) x gravitational field strength, g (N/kg)
Assessable content statements:
P2.3a explain that to stretch, bend or compress an object, more than one force has to be applied
P2.3b describe the difference between elastic and plastic deformation (distortions) caused by stretching forces
P2.3c describe the relationship between force and extension for a spring and other simple systems (to include graphical representation of the extension of a spring)
P2.3d describe the difference between linear and non-linear relationships between force and extension
P2.3e calculate a spring constant in linear cases
P2.3f calculate the work done in stretching
P2.3g describe that all matter has a gravitational field that causes attraction, and the field strength is much greater for massive objects
P2.3h define weight, describe how it is measured and describe the relationship between the weight of an object and the gravitational field strength (g)
P2.3i recall the acceleration in free fall
This subtopic focuses on the application of forces in stretching materials and force multipliers. A simple Key Stage 3 experiment of ‘stretching a spring’ using a range of different masses could be undertaken to recap the relationship between force and extension of a spring. Learners should be introduced to key ideas such as Hooke’s law and energy related to stretched objects. Keywords such as elastic deformation, plastic deformation, linear, non-linear will need to be introduced. Through experiments related to Hooke’s law learners could use graphs to share ideas with peers about what they could mean and analyse them mathematically. This could cover specification statements P2.3a–f.
Experiments relating to moments, hydraulics and gears will enable learners to understand how forces can be multiplied but many of these ideas will be new concepts. Turning forces can be simply related to see-saws for calculations whilst syringes full of liquid can be used to help learners to understand how hydraulic systems work and can be applied.
Common misconceptions or difficulties learners may have
Learners may find new terminology difficult to understand such as plastic deformation. To overcome difficulty learners could be provided with keywords with their definitions and a labelled graph for different types of material. Alternatively they could try and predict the shape of graphs for materials that are, for instance, brittle.
Learners may find understanding the rotation effect of gears difficult. When one gear turns clockwise the second gear in contact turns anti clockwise. To overcome this difficulty, plastic cogs found in toys for younger children could be used to physically show learners how they work.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
Acceleration when free falling is a good introduction to speed and everyday accelerations. The knowledge and understanding of ‘Forces in action’ builds on the work covered previously in subtopic P2.1.
Approaches to teaching the content
Learners are to be entered into a competition to compete for a position to become a car company’s new scientific trainee engineer. In order to become successful they must first beat the rest by showing off their knowledge of Physics. Learners must research and complete the following areas:
1. Draw outline of a car and label position of gears and suspensions.
2. Explain how suspensions work using Hooke’s law and spring constant (P2.3 a, b, c, d, e, f ).
Each group must present their research and knowledge to the rest of the group.
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