Negative Acceleration: Understanding Movement Direction

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SUMMARY

The discussion clarifies the concept of negative acceleration, specifically addressing the confusion surrounding its interpretation without given velocity. It establishes that negative acceleration, such as a = -5 m/s², does not inherently indicate whether an object is moving forward or backward; this is determined by the chosen reference direction. The term "retardation" is defined as acceleration acting opposite to the velocity, which reduces speed, while orthogonal acceleration results in curved trajectories without altering speed, referred to as centripetal acceleration.

PREREQUISITES
  • Understanding of basic physics concepts, particularly acceleration and velocity.
  • Familiarity with the definitions of positive and negative directions in motion.
  • Knowledge of the concept of retardation and its implications on speed.
  • Basic comprehension of centripetal acceleration and its effects on trajectory.
NEXT STEPS
  • Research the mathematical representation of acceleration and its effects on motion.
  • Explore the principles of kinematics, focusing on velocity and acceleration relationships.
  • Study the concept of centripetal force and its role in circular motion.
  • Investigate real-world applications of negative acceleration in various physical systems.
USEFUL FOR

Students of physics, educators teaching motion concepts, and anyone interested in understanding the dynamics of acceleration and its effects on movement direction.

sallychan
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I know that "negative acceleration" can be slowing down, or going backward and speeding up. I read the old posts here and I am still confused.

If no velocity are given, and you only know that the acceleration is, say, a= -5 m/s^2, how do you know the object is going forward or backward?
 
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sallychan said:
IIf no velocity are given, and you only know that the acceleration is, say, a= -5 m/s^2, how do you know the object is going forward or backward?

Hi sallychan. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

You don't know anything about the current velocity (or displacement) when all you are told is acceleration.
 
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What is "positive" direction and what is "negative"?
That is an arbitrary choice WE make!
When we use the concept of RETARDATION then that means the acceleration is in opposite direction of the velocity, where "opposite" means along the same line the velocity lies, but in the other direction (that is, 180 degrees shifted from the velocity direction). Retardation always reduces the SPEED of the object.

If the acceleration is ORTHOGONAL to the velocity, that is with a direction 90 degrees to the direction of the velocity, the acceleration will not change the speed of the object, but will make its trajectory curved, the sign of the acceleration telling us to "which side" the object will curve. We call such acceleration centripetal acceleration.
 

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