Hey, Erm so I was looking up threads that might actually help in Paper 5 [considering I have my mock exam tomorrow] but I couldn't really find one, so decided to post one. Things You Should Know For: Design, Analysis and Planning VARIABLES Scientists use an experiment to search for cause and effect relationships in nature. In other words, they design an experiment so that changes to one thing causes something else to vary in a way that the scientist can describe as a 'trend'. The most useful way to describe a trend is a mathematical one. These changing quantities are called variables, and an experiment usually has three main kinds: independent, dependent, and controlled. *The independent variable is the one that is changed by the scientist. In an experiment there is only one independent variable. This is usually plotted on the X-axis of the graph that the scientist uses to display his/her results in. As the scientist changes the independent variable, he or she observes what happens. *The dependent variable changes in response to the change the scientist makes to the independent variable. The new value of the dependent variable is caused by and depends on the value of the independent variable. For example, if you turn on a water tap (the independent variable), the quantity of water flowing (dependent variable) changes in response - the water flow increases. The more open the tap - the faster the flow of water. The number of dependent variables in an experiment varies, and there is often more than one. *Experiments also have controlled variables. Controlled variables are things that would have an effect on the dependent variable. S/he must be sure that the only thing affecting that variable is his/her adjustment to the independent variable. So, controlled variables are quantities that a scientist needs to keep constant, and s/he must observe them as carefully as the dependent variables. For example, if we want to measure how much water flow increases when we switch on a tap, it is important to make sure that the water pressure from the water supply (the controlled variable) is held constant. That's because both the water pressure and the opening of the tap valve have an impact on how much water flows. If we change both of them at the same time, we can't be sure how much of the change in water flow is because of the faucet opening and how much because of the water pressure. Most experiments have more than one controlled variable. Some people refer to controlled variables as "constant variables." *INTRODUCTION Whenever you design an experiment you have to first 'set the scene'. You are not ever finding anything out without any preconceptions. You always have ideas about what you are going to find out - you have expectations! In a science experiment these expectations will be based on: - what you have experienced in life, -experiments you have carried out before and -scientific knowledge (things you have been taught about science at school, or have found out from books). *In your report you need to explain to the reader what you expect to find out and why! *You do not have to look into a crystal ball and write down numeric predictions... just predict a general trend. A good way to do this is to sketch a graph! *You do have to explain the main scientific ideas that your prediction is based on. Try to use scientific keywords in this section and explain in simple terms what you understand them to mean. A Fair Test A fair test situation is vital for an investigation's results to be meaningful. You therefore have to use the scientific knowledge you have explained to identify the variables in your investigation - things you have to control, otherwise it will not be a fair test. Say what will need to be controlled and why - using theory to explain it. One of the variables will be the variable you are going to change. Say which on you are going to change and by how much (the range over which you will change it). Say how you found out that was a suitable range. It may well be your preliminaries that helped you decide on a suitable range! Then say have you are going to control all of the others you have identified. Your fair test must be linked to your scientific knowledge. *PRELIMINARY READINGS You will have a rough idea of what you want to do, but will need to 'tweak' your idea by trying things out practically. You therefore sketch out a rough experimental procedure and test out the best way to do it in a preliminary session.You may want to: - choose materials to work with: check that you will get a big enough range of readings with the ones you have chosen to investigate. - find out if you are controlling the other variables well enough to have a 'fair test'.... maybe you will spot some you hadn't thought of! - practise using the equipment, and see if you need to make adjustments to avoid or minimize errors.... or make it safer! - spot dangers in your procedure that you ought to avoid. Always check with a teacher before you carry out preliminary experiments - they have more experience at spotting potential dangers than you do!!What you find out from your preliminary readings will influence your final design of your experiment. Remember to say in your report if you found out a better way to do it from preliminary work.... and how you checked your ideas were sound before proceeding. .