# Three accelerators in a car

1. Oct 10, 2009

### fattydq

How many "accelerators" do you have in your car? There are at least 3 controls in the car which can be used to cause the car to accelerate. What are they? What accelerations do they produce?

I simply do not understand this question...are they talking accelerations within the car, or acceleration OF the car as a whole and even still I don't understand...

2. Oct 10, 2009

### mgb_phys

Remember that acceleration can be negative

3. Oct 10, 2009

### fattydq

Ok so the gas pedal in drive and reverse I suppose, but there's still a third? And what does it mean by what type of acceleration?

4. Oct 10, 2009

### mgb_phys

Acceleration has a different meaning in physics than everyday
Acceleration is rate of change of velocity, what does negative accelration mean?
How else do you change the velocity in a car.

5. Oct 10, 2009

### fattydq

Ahhh, braking! Right? Negative acceleration just means the velocity is decreasing, so if you go from 0 to 55 mph, then hit the break to stop accelerating to keep at a constant speed, you have negative acceleration?

6. Oct 10, 2009

### mgb_phys

Almost, braking is negative acceleration - so if you go from 55mph to 0 in 10seconds you have an aceleration of -5.5mph/s or -2.5m/s^2