Hi and welcome back to freesciencelessons.co.uk. 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 at the method for this practical. The practical requires two people to work together and we'll call these person 1 and person 2. Person 2 will measure the reaction time of Person 1. First Person 1 sits on a stool with good upright posture. Person 1 then places the forearm 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 a ruler vertically.
The zero centimetre mark should be between Person 1's thumb and first finger. Person 2 then tells Person 1 to prepare to catch the ruler. Person 2 now drops the ruler at a random time. Person 1 has to catch the ruler with their thumb and first finger, as quickly as possible when it drops. Person 2 now records the measurement on the ruler, that's level with the top of Person 1's thumb.
At this point Person 1 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 a reaction time. And to do this we use a conversion table. And there are plenty of these on the internet.
At the end the two people switch places, with person 1 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 their 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 are several control variables in this experiment. Firstly, the starting 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 control variables 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 hand and then with the non-dominant hand of the same person.
Because the dominant hand is the hand we use 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 drinks 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 their normal reaction time. Now because we're giving our test subject 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 an 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 clicking on the link above.