Kinematic Direction

[texan2414]

This might be a stupid question but,

Do objects always pursue their velocity in the direction of their acceleration?
Also, what exactly does deceleration mean? That the object is accelerating in the opposite direction of its moving velocity?

Thanks,

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[Cawolf]

No. An object can be moving rightwards but slowing down (accelerating opposite the direction of velocity).

Deceleration is exactly as you said, acceleration that decreases the magnitude of velocity.

This may be seen commonly in problems with a car braking.

Eg. This car is traveling along the positive x axis with a v = 30 m/s. The brakes are applied and a constant acceleration of a = -5 m/s^2 (deceleration) begins; how long does it take for the car to stop?

 

[texan2414]

@Cawolf

Thanks for your response. In your example, to deplete 30 m/s of velocity at a rate of -5 m/s^2, you would need 6 secs?

 

[Cawolf]

v = v0 + at

at = v - v0

t = (v - v0)/a

= (0 - 30 m/s)/(-5 m/s^2)

= 6 s

Yes. Acceleration is the change in velocity per unit time, so you "lose" 5 m/s every second.