# Can an object have zero velocity and still be accelerating? (b) Can an object have a constant velocity and still have a varying speed?

In each case, give an example if your answer is yes; explain why if

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• Anónimo
hace 1 mes
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For the first part, a), the answer is yes. For example, when the  piston in a car reaches the top of it's stroke it is momentarily stationary  but it then reverses direction giving a change in it's velocity's direction  producing an  acceleration.

b) The answer is no. Speed is just how fast a object is moving. However, velocity is speed with direction. if the velocity is constant then by definition both the speed and direction must also be constant too.

• hace 1 mes

Yes, Velocity is speed in a direction. (10MPh North).

A weight on a string in a circle is speed without direction so velocity is zero.

No, I don't thing so. change speed and velocity changes.

• Dixon
Lv 7
hace 1 mes

You have some good answers for a).

For b) I would just want to clarify that that truely constant velocity, ie constant speed and constant direction must be constant speed. However, constant velocity in a given direction can be achieved with varying speed if the direction of the path changes.

• Amy
Lv 7
hace 1 mes

(a) An object could momentarily have zero velocity while accelerating. Acceleration means velocity is changing; it could be changing from -1 to 0 to +1.

(b) Speed is just the magnitude of velocity. If an object has constant velocity, then it has constant speed.

(The opposite is not true: an object can have constant speed and varying velocity if it changes direction)

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• hace 1 mes

a) Yes.  It is quite obvious.  If it COULDN'T have an acceleration at zero velocity it could never GAIN any velocity so no object could ever start moving.  b) No.  If the velocity is constant then BOTH the speed AND the direction are unchanging by definition.    Note that an object CAN have constant speed but varying velocity if the direction of motion alters

• hace 1 mes

Velocity is a vector, so it has magnitude and direction.

So let's say your car is sliding backwards down a hill and you press the gas pedal in order to propel it forward.  Assuming you're successful, you will slow the reverse motion to a stop and begin moving forward.  There will be a moment, no matter how brief, when the car isn't moving at all (0 velocity), but the velocity will be increasing (positive acceleration).

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