# Mini-Quiz: Convention for Direction in Gravity Equations

by Ron Kurtus (revised 15 March 2011)

Take this Mini-Quiz to check your understanding of the lesson material.

1. Why isn't "up" considered positive as it is in the x-y coordinate system?

There is no such thing as upward or downward in the x-y coordinate system

Since the force of gravity is downward, it is more logical to have that direction as positive for gravity studies

Many people have wondered about that convention

2. From where is the displacement of a projected object measured?

Displacement is measured from the starting point

Displacement is always measured from the ground

Displacement varies according to distance traveled

3. If a ball is thrown upward, what sign is its velocity on the way down?

It is negative, since it started going upward

It is positive, since it is moving toward the ground

It depends whether the displacement is positive or negative

If you got all three correct, you are on your way to becoming a Champion in Physics. If you had problems, you had better look over the material again.

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## Resources and references

Ron Kurtus' Credentials

### Websites

Vectors and Direction - Physics Classroom

Gravity Resources

### Books

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www.school-for-champions.com/science/
mini-quiz_gravity_direction_convention.htm

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