# Physics Laboratory (Projectile Motion)

## Homework Statement

I'm doing this experiment in physics laboratory (I) about projectile motion and I'm concerned about some of the results (range) I'm getting. I'm using spherical projectiles about 3.0 cm wide (diameter).

Here's the thing, with the launch angle from 10 to 20 (thus, from 80 to 70) I'm getting everything as the theory predicts.

However, when I launch it at 45 (max range) or even 40/50 I get a maximized range but I get deviations of the balls in the y axis, meaning that |Δy|>0 (and not ≠0 as it should be).

## Homework Equations

I've asked my professor and even suggested the cause of it being the aerodynamics of the balls along with the friction force but he denied it and didn't give me a straight fulfilling answer.

## The Attempt at a Solution

My 'theory' about these deviations is that the farther a ball travels, the more time it's subjected to the friction force (obvious) and so, along with variations of pressure (due to its movement) the ball is forced to deflect (rotate) to the left or right. Again, I'm not sure this is true.

I could really use some feedback from you guys :tongue:

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BruceW
Homework Helper
Do you mean you get deviations in where the ball lands? (I'm assuming that's what you are measuring). You were saying the ball is deflected to the left or right. So that means the ball lands somewhere which is not along the direction it was launched in? And so the 'y axis' is horizontal and perpendicular to the launch direction?

Do you mean you get deviations in where the ball lands? (I'm assuming that's what you are measuring). You were saying the ball is deflected to the left or right. So that means the ball lands somewhere which is not along the direction it was launched in? And so the 'y axis' is horizontal and perpendicular to the launch direction?
Exactly and I'm sorry for not being clearer. What do you think?

BruceW
Homework Helper
I can think of another possible reason that doesn't involve friction. But your explanation sounds reasonable too. I think maybe you need to explain your theory more. You've said the friction force deflects it to the side, and that the longer its in the air, the more this deflection is. So starting with a small deviation in the position, or spin, or whatever of the ball, then in what way does friction act to magnify this, and how does this affect the lateral position of the ball?

What's your reason not involving friction?

Those deflections lead me to believe that the ball rotates. I don't know what's the dynamics behind it while it's in the air, I mean, I do but not with accurate precision. I imagine that while the projectile is in the air, friction as long with pressure variations play a part by introducing spin onto the ball, just maybe.

Other cause that can explain the desviations may be due to the launcher. Perhaps, when it's initially launched, the launcher gives the ball a small but signficant rotation and as it progresses along its path, it contributes to deflecting from the x axis. The farther it travels, the more it deflects.