Equations of Pjojectiles

A projectile is a body that falls freely under gravity ie the only force acting on it is gravity. In fact this is never strictly true, since there is always air resistance for example, but these other forces are small compared to gravity in most circumstances so we ignore them.

We can resolve the initial velocity of the ball vertically and horizontally as shown:

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The horizontal velocityis constant since there are no horizontal forces acting – gravity acts vertically. Horizontally therefore

Vertically however, the particle is accelerating downwards. We usually take this acceleration as negative and equal toVertically, we can apply all the normal suvat equations:

We get,




becomeswhich we have already.

We can also derive an equation betweenandby rearranging (1) to giveand substituting this into (3):


We can find the maximum height usingwithobtaining

We can find the range by substitutingin (5) to getSincethe maximum range is given bywhen