Acceleration due to gravity during its journey up and downWhen we throw an object up into the air, ignoring air resistance, etc, we define acceleration to be -9.8 m/s^2. When it goes down after its journey up, like a parabola, do we define the acceleration as 9.8 m/S^2, OR still the same as -9.8m/s^2?I know that acceleration due to gravity is always constant, but would it be wrong to say it like the question i have above?

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Eden Bradshaw · Accepted Answer

The simple answer is yes it does stay the same   −  9.8  m      s          −      2       because the acceleration is always pointing downwards towards the earth so we keep the minus. if you change coordinate systems you will need to change the result but with being close to the earth allowing to approximate the acceleration due to gravity to a constant which is in this case   9.8  m      s          −      2       with the downward direction assumed to be the negative direction we will keep   −  9.8  m      s          −      2       for all constant acceleration equations in the earth&#039;s gravitational field.

Peia6tvsr · Accepted Answer

The sign used for expressing the acceleration due to gravity totally depends on you. If the acceleration is in the opposite direction of your velocity then you can take any of them as positive or negative . By convention , since the acceleration is in downward direction and it opposes the motion we take it as negative.When the ball comes down , its velocity and acceleration due to gravity both are in the same direction i.e the velocity is increasing with time . So here you can take both of them to be positive or both of them as negative (as per your convenience).It doesn&#039;t matter but it&#039;s better to use these quantities with assigned sign convention .Hope it helps

Acceleration due to gravity during its journey up and down When we throw an object up into the air

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