[Music] hi and welcome back to three sighs lessons Cole you K by the end of this video you should be able to describe how to measure a person's reaction time and this is a required practical so it's important that you learn the details we're going to start by looking the method for this practical the practical request to people to work together unlike all these person 1 and person to person 2 will measure the reaction time of person 1 first person one sits on a stool with good upright posture person 1 then places the form of their dominant arm across the table with their hand overhanging the edge if you're right-handed then your dominant arm is your right arm now person 2 holds of Luna vertically the zero centimeter mark should be between person one's thumb and first finger person two then tells person one to prepare to catch the ruler person two now drops the ruler at a random time person one has to catch the ruler with the thumb and first finger as quickly as possible when it drops person two now records the measurement on the ruler that's level with the top of person ones thumb at this point person one has a short rest the test is then repeated several times and a mean is calculated from these experiments we can convert our results to reaction time and to do this we use a conversion table and there plenty of these on the Internet at the end the two people switch places with person one testing the reaction time of person 2 this allows us to see whether the two people have different reaction times now in any experiment the independent variable is the one that's changed so in this case the independent variable is the person having the reaction time tested the dependent variable is the one that's measured for each change in the independent variable so in this case the dependent variable is the reaction time control variables are ones that we don't allow to change and there were several control variables in this experiment firstly the stove working distance between the thumb and the first finger should be kept constant secondly we should always measure the ruler at the top of the thumb and lastly we should keep the conditions in the room the same for example the lighting and the level of background noise if we allow any of the controls I was to change then this could affect our dependent variable in other words the reaction time now in this experiment there are several other independent variables that we could investigate for example we could investigate the effect of practice in this case one person would catch the ruler a large number of times we would then look to see if the reaction time changes depending on the number of tries we might expect that the reaction time would become shorter the more the person practiced we could also investigate whether the reaction time depends on the hand catching the ruler in this case we would carry out the test with the dominant arm and then with the non-dominant hand of the same person because the dominant hand is the hand we used most often we might expect that the reaction time is shorter with the dominant hand compared to the non-dominant hand we could also investigate whether certain chemicals affect reaction time for example caffeine to do this the test subject runs a measured amount of Cola half an hour before the experiment and then we compare this reaction time with their normal reaction time the problem here is that there could be some other chemical in the cola which is affecting the reaction time to check that we'd also have to carry out the test using a caffeine-free Cola and compare this reaction time with a normal reaction time now because we're giving our test subjects something to drink we need to be certain that this is safe we should check that they have no medical issue which might be affected by caffeine for example in allergy or a heart condition and finally we need to carry out the test in a lab where hazardous chemicals are not normally used remember you'll find plenty of questions on this required practical in my vision workbook and you can get that by click on the link above [Music]