P2.2 Newton’s Laws
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P2.2 Newton's Laws
Mathematical learning outcomes:
PM2.2i recall and apply force (N) = mass (kg) x acceleration (m/s2)
PM2.2ii recall and apply: work done (J) = force (N) x distance (m) (along the line of action of the force)
PM2.2iii recall and apply: power (W) = work done (J) / time (s)
PM2.2iv recall and apply: momentum (kgm/s) = mass (kg) x velocity (m/s)
Assessable content statements:
P2.2a recall examples of ways in which objects interact
P2.2b describe how such examples involve interactions between pairs of objects which produce a force on each object; represent such forces as vectors
P2.2c represent such forces as vectors
P2.2d apply Newton’s First Law to explain the motion of an object moving with uniform velocity and also an object where the speed and/or direction change
P2.2e use vector diagrams to illustrate resolution of forces, a net force, and equilibrium situations (M4a, M5a, M5b)
P2.2f describe examples of the forces acting on an isolated solid object or system
P2.2g describe, using free body diagrams, examples where two or more forces lead to a resultant force on an object
P2.2h describe, using free body diagrams, examples of the special case where forces balance to produce a resultant force of zero(qualitative only)
P2.2i apply Newton’s Second Law in calculations relating forces, masses and accelerations
P2.2j explain that inertia is a measure of how difficult it is to change the velocity of an object and that the mass is defined as the ratio of force over acceleration
P2.2k define momentum and describe examples of momentum in collisions
P2.2l use the relationship between work done, force and distance moved along the line of action of the force and describe the energy transfer involved
P2.2m calculate relevant values of stored energy and energy transfers; convert between newton-metres and joules (M1c, M3c)
P2.2n explain, with reference to examples, the definition of power as the rate at which energy is transferred
P2.2o recall and apply Newton’s Third Law
P2.2p explain why an object moving in a circle with a constant speed has a changing velocity (qualitative only)
Approaches to teaching the content
Forces are covered at Key Stage 3 so learners should have a good grasp of the basic concepts. However this sub-topic covers a number of new areas that they may not be as familiar with. Forces acting as pairs and application of Newton’s three laws will be new material. Alongside this the skill of drawing scale vector diagrams may have to be covered.
Momentum, inertia and vector diagrams alongside the concepts of inertia and circular motion could be taught with practical demonstrations or application to real life contexts. They rely on learners being skilled enough to make the vector-scalar distinction. Be aware that learners will already have come across many of the terms used in this topic in an everyday sense and the scientific meanings and uses of these terms will need to be reinforced.
Common misconceptions or difficulties learners may have
Learners often have difficulty grasping the link between forces and motion, believing that no motion means that there is no force and also that no force leads to a lack of motion. Another concept that learners find difficult to understand is that of a reaction force e.g. the reason why the object doesn't fall is that the table is in the way, rather than that the table is exerting a force on the object. It can be difficult for learners to grasp elastic and inelastic collisions as, again, any demonstrations that we can perform are likely to be flawed by the presence of friction or air resistance. In these cases, simulations can be particularly helpful.
This simulation is particularly useful if an air track is not available to demonstrate elastic and inelastic collisions.
Clicking on the ‘more data’ button allows you to see the velocity of each ball and carry out momentum calculations should you wish to do so.
This could be used as a self-assessment tool or plenary quiz to check understanding of interaction pairs.
Learners are challenged to identify the interaction pair in different situations. Answers are given on the page.
A worksheet with answers to answer questions of circular motion.
There is some context within the questions but some questions on stellar evolution that are not covered in this subtopic.
Approaches to teaching the content
Contexts such as sports and moving vehicles are ones that many learners will be able to relate to and can be adapted to different groups of learners to match their interests. Events such as the Olympics provide many opportunities to analyse forces and motion in different situations. Activities such as roller blading can be used to introduce situations with little or no friction and compare them to walking on a floor, as learners may find it difficult to grasp the fact that we require friction between the floor and our shoes to allow us to move.
It may be useful for learners to consider their own bodies when considering forces, as this is something that is very concrete. For example, ask learners to consider how they can stay upright if someone was trying to push them over. This helps to reinforce the idea that objects can remain still, even when there are forces acting.
This could be used as a plenary activity to summarise resultant forces and a good revitaliser during a lesson which could be quite calculation heavy.
Learners jump in the direction of the resultant force.
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