Let’s Get Physics-l: Car Stopping Distances

Cars are something humanity have become rather dependent on (Whether or not that is a good thing is something I’ll leave to you to decide). Hence, it shouldn’t be a real surprise that something as over-arching as Physics includes stuff about cars. Now, I’m not going to be looking at the inner most workings of a car (Though that might be something I look into) but more about distances and how they relate to safety (Which, in reflection, sounds as interesting as watching paint dry but fear not, I have tried to make it slightly more engaging).

Before we get started, let’s set the scene. Spider-man is heading home after a long day of tackling a rather large octopus-themed mech (Otto has really upped his game). His use of his Spider-cycle can be excused on these grounds, being a superhero is far from easy. However, a hero’s job is never truly finished and Spider-man comes into contact with Aleksei Sytsevich or, as he is more commonly referred to, Rhino. Spider-man has to stop his bike to avoid crashing with Rhino. Does he have enough room? Who knows! Let’s find out!

When we talk about distances and safety with cars we need to consider the three types: Thinking, Braking and Stopping. To best accommodate the scenario, we shall look at them chronologically.

Thinking Distance is the distance a car travels whilst the driver observes and reacts to a hazard on the road by applying the brakes (Or doing something bizarre like flip the vehicle, something I strongly advise against). It is the product of your reaction time in seconds and the speed of the car. The faster you’re travelling, the further your thinking distance. Now, what with his Spider-sense and all, Spider-man’s reaction time is pretty quick. Hence, his thinking distance is short.

Braking Distance, as one may be able to guess, is the distance travelled by the car whilst the brakes are applied. Brakes convert the kinetic energy of the car into thermal energy. This transfer in energy is equal to the frictional force of the car which brings it to rest. Assuming the brakes are in good condition, the car should come to rest within a good distance.

Now, both thinking and braking distances can be influenced by a number of factors. If your vehicle is travelling at great speeds, the distances will be far greater in both instances. In terms of Thinking distance, tiredness, drugs, distractions (Which includes music and passengers) and the age of the driver can play a big part in how far you travel whilst you react to the problem. Braking distance is influenced more by conditions including those of the road you are travelling on, your brakes and your tyres.

Stopping distance is simply the sum of thinking and distance as it is the overall distance you travel whilst attempting to stop. Not much else to be said here…

Summary

• Thinking Distance – The Distance travelled whilst reacting to a hazard
• = Reaction Time x Speed of Car
• Factors that increase it: High speeds, tiredness, drugs, distractions and age
• Braking Distance – The Distance travelled whilst the brakes are applied
• Decrease in Kinetic Energy = Energy Transferred (or Work Done) = Force applied to brakes x distance moved by vehicle
• Factors that increase it: High Speeds, road conditions, brake conditions, tyre conditions, mass of the vehicle.
• Stopping Distance – Sum of Thinking and Braking Distance.

Car Stopping Distances. Not the most exciting topic but one that is important. If you have any thoughts, feedback, questions or suggestions please feel free to leave them in the comments and I will respond appropriately. Thank you.