This is what I feel when a car brakes:
I get thrown forward (due to my momentum, no doubt)
Once the car comes to a stop, I get thrown back! I see other people move like this too, so it’s not only me.
My current theory is that a car is like a box on a spring (the suspension). When braking, the spring is stretched forwards. After the wheels stop, the car bounces back, which causes this.
However, I’ve noticed that when braking, if I release the brakes slightly (not completely) during the “throw forward” period, I don’t get thrown back! With my theory, this is because releasing the brakes allows the wheels to move to align to the body, not the other way around.
This is for UK style driving, maybe in the US people get thrown backwards then forwards instead.
You’ve got it exactly. As you apply brakes, you’re slowing the tires & wheels while the body “leans” forward a bit on its suspension (springs, shocks, struts, etc.).
If you just leave the brakes applied at a constant setting until you stop moving, then all the leaning unwinds at that point and the car body rocks back a bit to get the body back to being centered over the wheels.
If, as you approach zero speed, you gently reduce the amount of braking, the forward lean will unwind slowly over those last few of feet of rolling. What happens then is the car body is slowing down slightly slower than the wheels are, and the wheels “catch up” to being directly under the body just as yuo come to a stop. Or even slightly before.
The big perceptual difference is that your body is less sensitive to small changes in acceleration than larger ones. And its much more sensitive to changes in direction of the acceleration. By gently unwinding the car’s body lean in those last few feet you make the stop feel much smoother.
Good limo drivers try hard to acheive this on every stop.
Agree that it’s mostly due to the front suspension springing back when the car halts. The harder you brake, the greater the compression of the front springs. Once the cars stops, this energy is released suddenly.
A secondary factor is that you are probably bracing yourself in the seat without realising it.
I don’t think people in the states typically drive backwards.
Ah ok it’s a straightforward and common observation then. Sometimes I try and release the brakes so it stops more smoothly too. I thought I was the only one to do this.
It is made more prominent because just before the vehicle stops the brakes work at maximum efficiency (static vs. dynamic friction). So the force exerted on the vehicle by the brakes spikes just before you stop, pulling you from your seat -> you bracing yourself -> the vehicle stops, the force exerted on the vehicle = 0 -> You push yourself back into your seat, battling a force that is suddenly absent.
Ah how can we tell which effect is at play? What about cars without suspension, trains etc? If it’s the secondary effect I should try slumping at the maximum forward force.
