What do you think of when you hear the word work? To get the students thinking ask them what do they think of when you say the word work. I generally find the students suggest things like homework, job etc. Then you want to explain to them that your going to look at the scientific kind of work that can be measured, as you cannot measure how much work (thinking) was done during doing homework.

Work Work is done when a force moves something Formula SI Units force × distance moved SI Units (N) × (m) = joules (J) This is the key information on the topic of work. You can get the students to pick out the key information from the text book before putting it up on the slide this way they have to think about it before you tell them. When it comes to the units explain to the students that they need to be careful when it comes to the units for work as you cannot work them out from the formula as you can in speed, velocity and acceleration.

Question - Work A man lifts a box from the floor with a force of 20N and lifts it on to a table 3m high. How much work is needed to lift the box from the floor to the table? Again the key to helping the students learn and understand the key information is to practice using the information in questions. This slide is a question on work and you should ask the students how do they think you could work out the answer. You can get them to tell you orally before you go to the next slide to show the working out of the question. Get different students telling you the different steps. Step 1: formula = force x distance moved Step 2: Work = 20N x 3m Step3: Work = 60N

Calculations Work = force × distance moved Work = 20 N × 3m Work = 60 J Show the students the working out of the problem and get them to practice some similar problem. Again get them working in pairs or groups for the first 1 or 2 questions depending on time. Then get them working independently with you giving help to individually who need assistance. Get the students to do a question independently. To reinforce learning give similar questions for homework. Chapter Summary

Work & Energy Energy is the ability to do work When you do work you are also converting energy from one form to another Having got the students thinking of the different form of energy you want to help them to make the link between work and energy. Remind them of the definition for energy-energy is the ability to do work. Get the students to think of some examples. When you walk/run you are doing work and you are also converting potential energy into kinetic energy. Practical example: You can also use a book on the desk and slide the book across the table, ask the students are am I doing work? Answer: yes Ask the students am I converting energy? Ask them what is the conversion taking place? Potential into kinetic.

Units of energy What are the units for work? joule When you do work you also convert energy What are the units for energy? You are trying to help the students to make the link between work and energy. You can first start by comparing the units. Getting the students to recall the units for work. Then get them thinking about the fact that when you do work you also convert energy. You can then ask them so what would the units of energy be? This way you will know the students that can/have make the link between work and energy. Here you could also great one of the students to explain to the rest of the class or preferably get the students working in groups of three and have the stronger student teach the weaker students. You will need to ensure the groups have even distribution regarding ability.

Question - Energy How much energy does Susan require to lift a large rock of 4 kg to a height of 3 metres? Work (energy) = force × distance moved Work (energy) = 40 N × 3 m Work (energy) = 120 J Some of the students will have made the link between work and energy, doing some questions this will help the rest of the students to make the link. In this example you are explaining that work and energy happen at the same time so when calculating energy you use the same formula as you use for work. In this question you are also getting the students to convert mass into force by multiplying the mass of 4kg by 10, because every 1kg = 10N. You will need to also explain that this 10N comes from the effect of gravity. You may need to spend a little time explaining this. Once you work through this example get the students doing some similar questions where you interchange the words work and energy and also use mass and force. This will get the students use to the idea of changing mass to force and also get them familiar with the relationship of work and energy. Chapter Summary

Work and Power Relationship Power measures the amount of work done in 1 second The power of the lamp is the amount of work it can do every second To spark interest Get 2 lamps and 2 different Watt bulbs (a 15 and 40 Watt bulb) and turn them on get the students to tell you which one is brighter. They can do this from looking at it and point to it. Then you can ask them why? At this point because you are only starting the topic they will not know and you can explain by the end of the topic they will know why. To close the topic you can return to these two lamps and bulbs and get them to explain why one is brighter than the other. They will be able to explain that the bulbs are different wattage and then you can show them the 2 bulbs – and that 1 is 15 Watts and 1 is 40 Watts.

Power Definition Formula SI Units Power is the amount of work done per second Formula Power = work / time SI Units Watt (1 J of work per second) Give the students the key information on power. Explain the Watt means that, 1 Joule is the work done (or energy converted) per second You want to put the emphasis on the connection between work and power, to calculate the power of a machine you must know (or be able to calculate) the work the machine can do first.

Question - Power If a toaster can do 50J of work in 2s. Calculate the power of the toaster? Power = work / time Power = 50 J / 2s Power = 25 watts This is a simple calculation for using the formula for power. The students only have to work out the power as they are told the work and time. Go through this question with the class. As the students get familiar with the topic again have a work sheet ready for them to practice some similar questions. Once the students are competent at these easier questions you could have some questions on the work sheet where the students must first calculate the work the machine does and then use the power formula to calculate the power of the machine.

Power ratings Household appliances have power ratings Chapter Summary To bring the lesson to a close you can finish off with talking about household appliances and getting the students to name some household appliances from their own homes that would have a power rating. The household appliances and the cost will be covered in the chapter on Electricity in the home later on. Chapter Summary