Forces


 * Forces**

Existing course days: Day 2: Size and time. Explanations. Introduction to forces. Day 3:: Newton's first Law. Balanced and unbalanced forces. Friction, moments and pressure. Day 4: Forces and motion. Speed, distance, time and acceleration. Day 5: Newton's second law, terminal velocity, calculations. Day 6: Momentum and impulse. Day 20 - Forces in 2d Day 21 - Circular motion and Simple Harmonic Motion

Probably of all the topics this is the most annotated within the pages for the days. Overall, this is one of the topics that you can have the most fun with. In my time as a physics teacher I suspended students from the ceiling with climbing ropes, hit them with baseball bats, had them pushing my car up and down the school driveway, made them lie on a bed of nails and all manner of other mayhem took place. Key message: do the risk assessment properly and try to have some fun with the topic. If you're not enjoying it and finding it interesting, why should your pupils? Although your students have an instinctive feel for some of the ideas in forces: friction, the conservation of momentum etc. they will still find some ideas hugely counter-intuitive. This is where it is vital to find out about their existing preconceptions. The idea, for example, that a car at one hundred miles per hour doesn't have any net force acting on it is just weird. Similarly, the idea that a concrete floor exerts a force equal and opposite to your weight is hard to grasp. Large-scale, memorable visual examples give students that nudge in the right direction. Calculations will rear their ugly heads in this topic too but at least in speed, distance and time problems you have situations that students are familiar with. It's a great context to get students to think about the importance of units - pretty much all of them will know a valid unit of speed and can work back from there to the formula - this leads to the idea that units can be treated as algebraic terms and rearranged in the same way. Up to KS4 work on forces will all be about Newton's laws. Balanced forces means no acceleration, so either no movement or straight line motion at a steady speed. The key skill for your students is to identify the forces acting in a situation and to identify what happens if the forces become unbalanced; consider objects in as many contexts and situations as you can with the widest variety of forces acting. Unbalanced forces means acceleration: one of the challenges here is that students have an embedded preconception that acceleration = speeding up. This will need repeated confrontation. To really understand this, students need to understand the difference between scalar and vector quantities - this can take time to sink in. Students should be able to clearly articulate the difference between speed and velocity. This leads on to the idea that a change in direction constitutes acceleration - by the end your students should be able to confidently explain that the Moon is accelerating toward the Earth. For more advanced students, certainly those that are going on to A-level, this is a good time to introduce the idea of resolving forces. (not the best example but fairly comprehensive). Momentum is a topic that a lot of people find difficult whilst having a very good instinctive grasp of: who's easier to catch as they jump from a first floor window - a child or a sumo wrestler? Which is harder to push start - a mini or a double decker bus? It's a fantastically easy topic to make dull, masses on trolleys rolling down runways and the like whereas there are unlimited chances to make it interesting. Design crumple zones for eggs on trucks, use Tracker to show that the acrobatic falls in chocky-sock movies are all faked, crack bullwhips, make slow-motion films, use bats, balls, punch bags and anything you can think of. Once you get into the A-level physics it can all get bogged down in maths quite quickly. Remember your own experiences of learning the A level material and plan your approach accordingly. Circular motion is a big step for many students if they're not doing maths A-level: they won't have come across radians and you're going to have to resign yourself to teaching a maths lesson or two. You could, of course, get a colleague from Maths to do it in your stead and cover a year 9 maths lesson in return - actually a good bit of professional development.
 * Teaching notes**