Reaction Time (AQA GCSE Physics): Revision Notes

Thinking distance is influenced by several factors:

• Vehicle speed: The faster the vehicle is moving, the greater the distance covered while the driver reacts.
• Reaction time: A slower reaction time means more distance is travelled before the brakes are applied.

Reaction time varies from person to person but generally falls between 0.2 and 0.9 seconds. Factors that can influence reaction time include:

• Tiredness
• Drugs
• Alcohol
• Distractions (e.g., using a phone, listening to the radio)

To measure a person's reaction time, using a standard stopwatch is ineffective since reaction times are typically less than a second. A simple alternative method is to drop a ruler and measure the distance it falls before being caught.

Method:

1. Place your hand at the 0 cm mark on a ruler, with your thumb and forefinger hovering over the spot. Have someone else hold the ruler from the top.
2. Without warning, the person holding the ruler should drop it. Your goal is to catch it as quickly as possible.
3. The point where your thumb and forefinger catch the ruler indicates the distance it fell during your reaction time. A longer distance means a slower reaction time.

Given that the acceleration due to gravity is 9.81 m/s², you can use this and the formula $v² = u² + 2as$ to calculate the actual reaction time.

To improve the accuracy of the experiment, repeat the test several times and calculate an average reaction distance or time. You can also experiment with how distractions affect reaction time.