Particle Movement: Understanding Direction in Physics

When is a particle moving in the positive direction?

a) When the velocity is positive b) When the velocity is negative c) When the acceleration is positive d) When the acceleration is negative

Final answer:

A particle is moving in the positive direction whenever its velocity is positive.

Explanation:

A particle is moving in the positive direction when the velocity is positive. In other words, the direction of velocity determines the direction of the movement of the particle. For instance, let's consider a case where at t = 1 s, the velocity v(1 s) = 15 m/s, which is positive, and the acceleration is also positive. This indicates that the particle is not only moving in the positive direction but also its speed is increasing because both velocity and acceleration are in the same direction. Conversely, if the velocity is negative (like moving to the left or downwards), the particle would be moving in the negative direction.

However, remember that acceleration doesn't always indicate the direction of movement, but the direction of change in velocity. For example, if a car is moving in the negative direction (with negative velocity) but slowing down, it has a positive acceleration because its velocity is becoming less negative.

As a rule of thumb, positive and negative in physics most often relate to a chosen direction, not good/bad or right/wrong. So, when we say a particle is moving in a positive direction, it's relevant to the orientation we've chosen (right, up, forward, etc typically being 'positive').