6 Slingshot science Teacher notes This virtual experiment illustrates the relationship between EPE and KE. It could be used as a precursor to running the practical in the lab, or as a revision exercise.
7 Investigating springs Teacher notesThis animation could be used as a revision activity, or as a precursor to running a practical experiment in the classroom.Students could design and carry out an experiment to find out k based on this and the next slide. A spring can be suspended from the edge of a desk and its length measured. Weights can be added to it to increase the force on it, and its new length measured for each weight added. Extension for each weight can be calculated by subtracting the original length from these values. A graph of weight (force) against extension can be plotted. The gradient of this graph is k.Other materials such as a rubber band or a polythene strip could also be tested to see if they obey Hooke’s law (discussed in further detail on slide 9), i.e. if they have a constant gradient for their force-extension graphs.Issues to discuss surrounding this experiment can include:Accuracy in measuring the length of the spring. Students should measure from the same point each time (the end of the coils as shown above, or the last coil).Safety – the spring could snap if overloaded, so safety goggles should be worn and a box should be placed underneath the weights to catch them if they fall.Have enough points been plotted on the graph to ensure as accurate as possible a line of best fit and therefore gradient?
8 limit of proportionality Resultsplastic regionforce (N)break pointlimit of proportionalityelastic limitelastic regionextension (cm)Teacher notesIt should be pointed out that the limit of proportionality is at the point where the graph is no longer a straight line. Students should be able to make sense of this since a straight line graph represents direct proportionality. The link between the definitions of elasticity and elastic limit could be highlighted – the elastic limit is the extent to which a material displays the property of elasticity.If a spring is stretched far enough, it reaches the limit of proportionality and then the elastic limit.The elastic limit is a point beyond which the spring will no longer return to its original shape when the force is removed.
9 Hooke’s lawThe limit of proportionality is a point beyond which behaviour of an elastic material no longer conforms to Hooke’s law:The extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded.F µ eorF = kewhere k is a constant.original lengthxTeacher notesF is the force in newtons, N; k is the spring constant in newtons per metre, N/m; e is the extension in metres, m. The stiffer a spring is, the greater its spring constant (k).F
12 Glossary Teacher notes compression force – A force that can squash objects, making them smaller.conservation of energy – The law that states that energy cannot be created or destroyed, just transferred into different forms.elastic – A material that can be returned to its original shape when deformed once the external force is removed.elastic limit – The point at which any larger force will cause permanent deformation of an object.elastic potential energy (EPE) – The energy stored in a object when stretched or squashed.energy transfer – A process by which one form of energy is transferred into another form.Hooke’s law – For elastic materials, force and extension are proportional provided the elastic limit is not exceeded.kinetic energy – The energy an object has because it is moving.limit of proportionality – A point beyond which the behaviour of an elastic material no longer conforms to Hooke’s law.plastic – A material that changes shape permanently when deformed by an external force.12
14 Multiple-choice quiz Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of elasticity. The questions can be skipped through without answering by pressing the forward arrow. Students could be asked to complete the questions in their books and the activity could be concluded by completion on the IWB.14