# How to know 'the displacement of a particle is 'negative'?

## Homework Statement

If x1 and x2 are the initial and the final position vectors of particle respectively. Then, displacement of the particle is delta x = x2 - x1
But my question is how to know that the displacement is negtivive and its direaction? (could you provide a practical example so that I can understand easily?)

2. The attempt at a solution

Only I know that if x2 is greater than x1, the the delta x is positive
If x1 is greater than x2, delta x is negative
if x1 = x2, then delta x is zero

## Answers and Replies

kuruman
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x2 must be less than x1
Example 1: x1 = -3, x2 = -5. Δx = x2 - x1 = -5 - (-3) = -5 + 3 = -2.
Example 2: x1 = 5, x2 = 3. Δx = 3 - 5 = -2

CWatters
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+1

Then, displacement of the particle is delta x = x2 - x1

You do that sum carefully taking into account the signs of x1and x2.

If the answer is negative then the displacement is negative.

• Medicalboy
+1

You do that sum carefully taking into account the signs of x1and x2.

If the answer is negative then the displacement is negative.
Could you provide a phenomenon example where we can see the negative displacement?

kuruman
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What is positive and what is negative depends on your choice of axes. If you use the standard convention, "to the right is positive and to the left is negative", then a car moving to the left has negative displacement over any time interval during this motion.

• Medicalboy
CWatters
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Could you provide a phenomenon example where we can see the negative displacement?
Kuruman has provided two examples.

Sent from my Hudl 2 using Physics Forums mobile app

PeroK
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Could you provide a phenomenon example where we can see the negative displacement?

It's not conceptually much different from monetary transactions. If you take money out of your account that's a "negative displacement" of your bank balance!