# Support page

## Video analysis of a projectile

### Objectives

• Practice using video analysis.
• Reinforce theory of projectile motion.
• Observe the effect of drag.
• Give some ideas for investigations.

### Notes

A couple of tricks that are worth knowing.

• To get rid of a dot click the arrow (select point tool) then using it click the point you want to remove and delete it. Using the select tool a point can also be moved around. This is a good way to place the points more accurately.
• If the video disappears its probably behind your graph, either that or you have deleted it which isn't good news.
• If you want the projectile to start from the origin then place the origin there using the set origin tool

There is quite a big difference between the ball and balloon, this is due to the influence of air being greater on the balloon than the ball. Buoyancy significantly affects the vertical acceleration and drag affects the speed.

Here the trajectories of the ball and balloon are compared on the same graph.

The difference in trajectory can clearly be seen although no real comparison can be made since the launch speed and angle were quite different.

Given the initial speed and angle it might be interesting to see how close the Excel model can predict the range.

The equation for the trajectory is $y=&space;y_{o}+xtan\theta&space;-\frac{gx^{2}}{2(vcos\theta&space;)^{2}}$ it is interesting to see if the values for θ and v obtained from the coefficients on the graph agree with this equation. you can check by measuring the distance and time between the first two dots on the video and use the onscreen protractor to find the angle. The values I obtained from my graph were quite close.

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