In your dreams, friction does not exist. Have you ever tried parking on a hill? You can't. Brakes don't work. I always have to enter conscious state, order the car to stay in one place, re-enter dream state and proceed as if nothing happened. (This is level 4, so hold on.) If you ever find your self unable to write or unable to stop something with friction, you can be sure you are dreaming.
Funny that you mentioned this. 2 nights ago I dreamed I was blasing through the streets with a Bugatti. It felt like I was on ice and one moment I drove the car straight into a lake. Bit of panic there, but gladly I quickly realized I was dreaming so I took a nap (in my dream) just where I was and woke up nicely in my own bed with no harm done.
If it were me the Me Ex Machina mechanic would have kicked in and helped me control it. That level is pretty fun :P you get to fix weird physics and bugs :P
Sure as hell I wan't to control this better. I had some lucid dreams and it was amazing. Lucid dreaming teaches us to understand the liquidity of our awake experience as well.
You can find the answers that you seek young grasshopper. So keep on practicing!