# Using Basic Physics to Develop Driving Scenarios

One of the best things about our STISIM Drive simulator is the flexibility you get when it comes to designing driving scenarios. Using the drives that come with the simulator, and our extensive technical library, you can customize a drive to gather whatever data you might need.

One thing to keep in mind, though, is that flexible doesn’t mean “free for all”. As you design your custom driving scenarios, you will inevitably need to use some basic physics to line up events and make things look realistic.

When you need to make things look as realistic as possible, we’ve found it immensely helpful to have a handy set of equations to use with constant acceleration problems. Stay with us here…

As with all physics equations, there are variables present. The variables used to describe linear motion are position (*x*), velocity (*v*), acceleration (*a*), and time (*t*). Below are linear equations of motion that use three of these variables at a time. Choose the equation that relates the given quantities with the desired variable that best fits your particular situation.

All of the above equations assume constant acceleration and linear dynamics. For STISIM Drive, the second equation will likely be the most useful because it does not have acceleration as a variable within the equation.

In general, when it comes to creating driving scenarios, you will be specifying positions, speeds, or time. Thus equation #2 can be used to find a value if the other variables are known. Since these equations assume that a variable will be changing from one value to another, they all have initial values associated with them. And, the equations above, the variables with the zero subscript denote the initial position and speed values.

Take this example for how you would use equation #2 in the simulator: Start with a simple parked vehicle that you want to pull into traffic. We want to know where the vehicle will be when it reaches full speed. The event line would look something like this:

**1000, Vehicles, 0, -6{1}, 0{0}, 1, S53, 1, 1, 5{0}, 2, 60{0}, , , 5**

The parameters we care about are:

x_{0} = 1000 (vehicle’s initial position)

v_{0} = 0 (vehicle’s initial speed)

v = 60 (vehicle’s final speed)

t = 5 (time for the vehicle to get up to speed)

Finally, we have the equation:

X = 1000 + (60 + 0) * 5 / 2 = 1150

Therefore, the vehicle will reach full speed at 1150 feet.

Hopefully this short tutorial helped you see how basic physics play an important part in scenario design for your simulator!