Thu February 17, 2011 By: Saurabh Parnerkar

Respected Ma'am I am Saurabh of class 11.I wanted to ask a question related to projectile motion.My question is Why do we take gravitation as negative in projectile it should be taken positive because the body during its filght is always under influence of gravitaion and also that finally it acts in direction the gravitation is.then it should be taken positive right???????????

Expert Reply
Thu February 17, 2011
Dear student,
It is negative if the upwards direction is defined as positive. Acceleration is downward.
The sign for the acceleration of gravity depends on which direction you choose to be positive for the vertical axis.If the positive direction is defined to be up (the usual convention), then the acceleration of gravity is negative (the acceleration vector points downwards, in the negative direction for the vertical axis).
Hope this helps.
Home Work Help