Projectile Motion
Projectile motion requires you to combine two equations - horizontal velocity and vertical acceleration. If you throw something, it is travelling in two planes: horizontally (or forward), and vertically (towards the earth).
Vertical and Horizontal Motion
Vertical Motion:
Say that you drop a ball from a height, gravity is acting as a force on the ball. This force causes the ball to accelerate towards the floor, at an acceleration of 9.8ms^-2 (Earth Gravitation Field strength). The time at which it hits the floor depends on the acceleration of the ball.
Often in these questions, you are asked to calculate the distance travelled by a projectile. In most questions, the first step is the calculate the time that it takes for an object to hit the ground, which is determined by vertical motion and not horizontal motion.
Horizontal Motion:
Horizontal velocity can be calculated using d=s/t.
If you were to kick a ball directly forward off of a hill, the ball would be propelled horizontally as well as towards the floor. The ball will continue to travel horizontally at a constant velocity, until it hits the floor (When ignoring friction). The time at which the ball hits the floor and stops moving is dependent on gravity and the vertical motion of the ball, not horizontal.
Projectile Motion
A projectile is an object upon which gravity is the only force active upon it. Therefore, projectile motion describes objects that have been launched. The motion of the object is determined by the horizontal motion of the object as well as the vertical motion, determined by gravity.
Combine the two equations given above to calculate unknown values in projectile motion questions.
Key Points!
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Horizontal Motion
Calculate horizontal motion using s = vt
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Vertical Motion
Calculate vertical motion using a = (v-u)/t
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Projectile Motion
Combine these equations to answer projectile motion questions.