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P5 V) Reaction Times
P5 V) Reaction Times
Reaction times are generally between 0.2 and 0.9 seconds. Reaction times are affected by many different factors such as drugs, tiredness, age, distractions, caffeine and many more. We can investigate how these factors affect reaction times by using the ruler experiment or a computer.
Ruler Experiment
The ruler experiment involves two individuals; A and B. A is the individual doing the testing, and B is the individual that is having their reaction time tested. The person being tested (B) rests their forearm on a table with their hand slightly over the edge of the table (we use a table so that the individual being tested is unable to move their forearm).
The ruler experiment involves two individuals; A and B. A is the individual doing the testing, and B is the individual that is having their reaction time tested. The person being tested (B) rests their forearm on a table with their hand slightly over the edge of the table (we use a table so that the individual being tested is unable to move their forearm).
The individual that is not being tested (A) then holds a ruler vertically between the thumb and index finger of the individual being tested (B). The zero marking on the ruler should be in line with the thumb and index finger. The ruler is then let go at a random point. The ruler is let go randomly because we do not want the individual who is being tested to anticipate the ruler being dropped or be told that the ruler is about to be dropped. This is because we want the experiment to test reaction time rather than anticipation. After the ruler has been dropped, the individual being tested will catch the ruler as quickly as possible. We record the number on the ruler where the thumb and index finger are when they caught the ruler. A smaller number means that the individual caught the ruler quicker and therefore has a faster reaction time. A higher number means that the individual caught the ruler more slowly, thus meaning that they have a slower reaction time. We repeat the experiment a few times and work out the mean. The more repeats that we undertake, the more reliable our results will be.
The experiment so far has given us a value for distance and not reaction time. We can calculate the reaction time by using two different formulas. Let’s suppose that I completed the experiment a few times and the mean distance that I caught the ruler was 25 centimetres. We are now going to work out the reaction time for this.
Step 1 – Final Velocity
The aim of the first calculation is to find the final velocity of the ruler by using the formula below.
The experiment so far has given us a value for distance and not reaction time. We can calculate the reaction time by using two different formulas. Let’s suppose that I completed the experiment a few times and the mean distance that I caught the ruler was 25 centimetres. We are now going to work out the reaction time for this.
Step 1 – Final Velocity
The aim of the first calculation is to find the final velocity of the ruler by using the formula below.
We are looking for the final velocity of the ruler which is the value of v. u in the above formula is the initial velocity of the ruler and as the ruler was stationary when it was dropped, the value of u will be 0 m/s. a in the above formula is acceleration and the ruler will be accelerating due to gravity; acceleration due to gravity on earth is always 9.8 m/s2. s in the above formula is the distance, which is measured in metres. The mean distance that I caught the ruler at was 25 cm, and we convert this to metres by dividing by 100; the distance in metres is 0.25 m (25 ÷ 100 = 0.25). We now sub in u as 0, a as 9.8 and s a 0.25.
We want to find the value of v and not v2. Therefore, we square root both sides of the equation.
The final velocity of the ruler is 2.21359… m/s.
Step 2 – Time
We use the second calculation to find the (reaction) time. We find the time by using the acceleration formula triangle and calculation below.
The change in velocity is 2.2135… m/s (the final velocity was 2.2135… m/s and the initial velocity was 0 m/s as the ruler was stationary; v – u = 2.2135… – 0 = 2.2135…). The acceleration is gravity, which is 9.8 m/s2. We sub these values into the formula.
We now round our answer to 2 significant figures.
Therefore, the reaction time is 0.23 seconds to 2 significant figures.
Computer
We can get a more accurate reaction time for an individual by using a computer with a reaction time program installed on the computer. The reaction time program would ask an individual to click the mouse or press a button as soon as a stimulus appears on the screen. The program will then measure the time between the stimulus appearing and the mouse being clicked/ button being pressed. The stimulus on the computer will randomly appear, which removes any anticipation from the individual being tested, thus meaning that the computer program gives us a truer reaction time compared to the ruler dropping experiment (in the ruler dropping experiment, the individual may anticipate when the ruler is dropped, which will affect the value for reaction time). Also, the computer can measure reaction times more accurately as it can measure reaction time in milliseconds. Furthermore, there is no possibility of human error when using a computer.
We can get a more accurate reaction time for an individual by using a computer with a reaction time program installed on the computer. The reaction time program would ask an individual to click the mouse or press a button as soon as a stimulus appears on the screen. The program will then measure the time between the stimulus appearing and the mouse being clicked/ button being pressed. The stimulus on the computer will randomly appear, which removes any anticipation from the individual being tested, thus meaning that the computer program gives us a truer reaction time compared to the ruler dropping experiment (in the ruler dropping experiment, the individual may anticipate when the ruler is dropped, which will affect the value for reaction time). Also, the computer can measure reaction times more accurately as it can measure reaction time in milliseconds. Furthermore, there is no possibility of human error when using a computer.
Investigating What Affects Reaction Times
We can investigate how different factors affect reaction times by completing the experiment twice; the first time will be the control test, and the second time will be where we change a factor that may affect reaction time. We then compare the results from the two experiments to see what affect the factor has on reaction time. Here are some of the factors that we can investigate to see what affect they have on reaction times; we only make these changes for the second test – the first test will be the control.
For all of the modifications above, we would only change one variable and keep all of the other variables constant (the same). For example, we would need to use the same table, the same ruler etc. Also, we would need to make sure that the individual is in the same state ignoring what we are changing/ investigating. For example, if we were investigating the effects of tiredness on reaction times, we would not want the individual being tested to have consumed any substances that we are not testing for (caffeine or alcohol) between the first test and the second test; this is because the consumption of other substances will influence the individual’s reaction time.
We can investigate how different factors affect reaction times by completing the experiment twice; the first time will be the control test, and the second time will be where we change a factor that may affect reaction time. We then compare the results from the two experiments to see what affect the factor has on reaction time. Here are some of the factors that we can investigate to see what affect they have on reaction times; we only make these changes for the second test – the first test will be the control.
- Caffeine – we can investigate the effect of caffeine on reaction times by giving an individual a caffeinated drink, such as a coffee, energy drink or cola. We then wait 15 minutes and then compete the experiment again (we wait 15 minutes because it takes a while for the caffeine from the drink to have an effect on the body). Caffeine should decrease reaction times – it will make reaction times faster.
- Alcohol – we can investigate the effect of alcohol on reaction times by carrying out the experiment again 15-30 minutes after an individual has consumed an alcoholic beverage (we wait 15-30 minutes because it takes a while for alcohol to have an effect on the body). Obviously, we should only investigate the effects of alcohol on individuals who are over the drinking age; above 18 in the UK. Alcohol will increase reaction times – it will make reaction times longer.
- Tiredness – we can investigate the effect that tiredness has on reaction times by completing one experiment during the day and the second experiment in the evening (such as 10 pm) when an individual will feel more tired. Tiredness will increase reaction times – it will make reaction times longer.
For all of the modifications above, we would only change one variable and keep all of the other variables constant (the same). For example, we would need to use the same table, the same ruler etc. Also, we would need to make sure that the individual is in the same state ignoring what we are changing/ investigating. For example, if we were investigating the effects of tiredness on reaction times, we would not want the individual being tested to have consumed any substances that we are not testing for (caffeine or alcohol) between the first test and the second test; this is because the consumption of other substances will influence the individual’s reaction time.
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