# What is the acceleration of a car at constant speed?

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1. Oct 2, 2015

### BoredButCurious

If a car is travelling at a constant speed of say, 60MPH, is the acceleration of the car 0, or is it equal to the drag and rolling resistance it's facing?

2. Oct 2, 2015

### phinds

What do you think and why? What is the definition of acceleration?

3. Oct 2, 2015

### @navin

If not considering resistive forces, the acceleration is zero.
But if we do consider them, then they are always opposing the motion of the car. To keep the velocity of the car constant, the engine has to be kept running, else resistive forces slow u down to rest.
So, a force is applied by the engine just to overcome the resistive forces to keep the car moving with constant velocity.
I hope you understood :-)

4. Oct 3, 2015

### CWatters

Read your question again. The last part asks if an acceleration (the acceleration of the car) is equal to a force (drag/rolling resistances are forces). That cannot be correct.

5. Oct 3, 2015

### sophiecentaur

You should also distinguish between speed and velocity is you are dealing with Acceleration in a thorough way.

6. Oct 3, 2015

### Drakkith

Staff Emeritus
I'm sorry but your explanation is overly complicated and confusing and has little to do with the OP's question.

As Phinds said, look at the definition of acceleration: the rate of change of velocity.

7. Oct 4, 2015

### Chandra Prayaga

As pointed out already, all such confusion arises because of not completely understanding a definition. First, constant speed does not mean zero acceleration. An object could be going on a curved path at constant speed. The object has an acceleration. Zero acceleration means constant velocity. Also to be noticed is that the definition of acceleration does not involve any information about forces. Acceleration is a kinematic quantity. Irrespective of what forces are acting, if the velocity is constant, the acceleration is zero.