Physics 2211, Lab 6: Projectile Motion

Eric Murray, Summer 2006

Required Advance Reading

The heart of the Projectile Motion concept is that horizontal and vertical motions are independent, linked only by time. It is a special case of motion with constant acceleration, so the constant acceleration kinematic relationships

x = x₀ + v_0xt + ½a_xt²

and

y = y₀ + v_0yt + ½a_yt²

can be used. If one lets the horizontal direction be x and the vertical direction be y, then a_x = 0, and the magnitude of a_y is 9.8 m/s² (its sign depends on which direction is chosen as positive).

In these experiments, the vertical displacement, y - y₀, and the magnitude of the initial velocity, v₀, will be measured. After finding the vertical component of the initial velocity, v_0y, the expected time of flight can be calculated. This time for vertical motion must be the same as the time for the horizontal motion, so the expected horizontal displacement, x - x₀, can be predicted and compared to the experimental results.

Note that the vertical component of the velocity is easy to calculate for a horizontal launch. For angled launches, however, it is very important that the sign of the vertical component of the velocity be consistent with coordinate axes that have been chosen.