this slide is just showing us more about science and this one specifically says experiments so the idea here is that when you conduct an experiment and you're testing your hypothesis you're going to test one variable one thing one item at a time if i want to know i've observed that plants given fertilizer seem to grow better and we're going to study the effects of fertilizer on plants so we have 20 plants and we're going to test one variable at a time one thing at a time the thing we're testing is fertilizer so we're going to have our test experiment and our control experiment i have 20 plants 10 of them are going to get fertilizer 10 of them are not going to get fertilizer we're going to say there are three main variables the first one's going to be our independent variable or the condition the condition here is well what condition are we studying we're studying right so that's the condition that's the independent variable the dependent variable is what we're going to measure what we're going to record what we're going to write down and our entire study depends on that that's really important and then the control variable are variables that are not changed start with the control variable because that's pretty obvious the control variable is controlled it's a variable that's not changed so in my example of studying the effects of fertilizer on plant growth what would you say what would some of the control variables be all of the plants have to have the same temperature same temperature 70 degrees fahrenheit boom done the amount of light they all need to have the same amount of sunlight either they're all out in the sun or they get each of they all go out for two hours water as well we want you want everything except the fertilizer so water pressure air temperature sunlight everything is controlled except one thing so the fertilizer so when you get a result you can say that it was because of the fertilizer and not because of other things so that's pretty straightforward now the dependent variable is what you're measuring so if we want to do something with plants and take measurements to see how well fertilizer worked what are the types of plant measurements we could take the growth the height and for growth there's many different ways to do that it can be the height it can be the width it can be the biomass it could be the number of leaves how thick they are how long or wide they are how thick the stem is there's many different ways and yours to measure the dependent variable your study depends on those results so these are usually numbers right or not always we have qualitative as well but for now we're saying what are you measuring what are you writing down right so that control variable and dependent variable are pretty straightforward what we're left with is an independent variable the independent variable is the condition that you're studying so here the independent variable is the fertilizer and one way to think about that is i am an independent researcher and i can independently decide what i want to study and independently decide the amount so i'm going to study fertilizer and its effects on plants and i independently am choosing fertilizer and i'm independently choosing the amount of fertilizer that that is independent once it's set it's independent we're just leaving it as is one thing we want to differentiate with these variables is control variable is different than control group control variable are those variables that we are not changing we're only changing or the only thing we're testing is the fertilizer that's the only thing so everything else has to stay the same the control group if you have that in your experiment means the group you're not doing anything to for example that would be the group that you're keeping everything the same except the thing you're not doing to them is they're not getting fertilizer so the temperature is the same the amount of water they're getting the same the sunlight's the same except the experimental group gets the fertilizer the control group does not so we can have 10 plants getting fertilizer and 10 plants not getting fertilizer so that's another way that we can compare our findings is it really due to the fertilizer well let's see what is the growth how tall what's the biomass how many leaves how thick is the stem or are the stems of the plants that were given the fertilizer versus the ones that were not so we have controlled variables variables we don't change and keep the same versus control group that's a whole group that you can compare to your experimental group and they do not get the experimental condition they do not get the independent condition they don't have fertilizer