Question #457db
1 Answer
That's not always true. The answer lies in
you.
Explanation:
Usually, when we do motion-problems, we integrate human experience in solving.
- In this case, we treat 0 as the ground and the positive y-axis as above ground and negative y-axis for below ground. where ground could be an elevated structure. Thus, when you take note of the vector of gravity
#g# , it points to below ground (in the negative y-axis). Hence, if you observe a particle released at ground, you would infer that it is influenced by the gravity that's pointing downward. Thus the value of gravity is taken negative. -
Additionally, we see that as the particle falls, its height, y, is going more and more negative. Thus the force acting on it must be negative too and since we know that the mass cannot be negative, the acceleration of the mass must be negative.
#F = ma, -F =m(-a)# -
Now if you then look at the problem upside-down (where your positive y-axis is pointing downward and the negative y-axis pointing upward) we can see that as the particle falls, its height, y, becomes more and more positive, hence we infer that the force acting upon it must be positive as well.
In conclusion, the sign of the value of gravity depends on how you look at a problem; if you look at it with positive y-axis pointing upward or pointing downward.
