Information from strobe light picture?

Question

I'm doing an investigation on the physics and motion behind a projectile for my physics class. The main theory that I'm verifying is Galileo's horizontal and vertical motion are independent motions. The way I have done this is I have gotten a tennis ball and rolled it down a ramp off a table of 90cm height, i have also dropped a tennis ball from a vertical height of 90cm and taken pictures of both of these with a strobe light.

What I am asking is how do I work out information from the pictures below? How do I get the acceleration, velocity of both the horizontal and the vertical? How do I work out kinetic and potential energy? the strobe was set to 20. Don't hesitate to ask any questions about the prac, if there is any really detailed answers, just send it to my email [e-mail] and just say you sent me an email and i'll give the points obviously to the answer that helps me most

Thank you for any help

http://img119.imageshack.us/img119/6595/imgp39622dx2.jpg

http://img504.imageshack.us/img504/2636/imgp39272ub1.jpg

Answer 1

Your experiment is sound, but unfortunately you have to know the exact timing of the flash - how many flashes per second. Without that you cannot make the calculations because you have to know the distances the ball traveled over each unit of time. If the setting of 20 means every 20th of a second you're OK, but if the strobe has just a dial then you may be out of luck. You could get relative measurements, but I don't think that is what you want.

The links below will help you with your calculations.

http://www.ugrad.math.ubc.ca/coursedoc/m...

http://books.google.com/books?id=zKHXqNT...

Answer 2

Draw line segments from the center of the circle to the center of the next one in the sequence.

Do this for all the circles in the sequence.

For the parabolic path "decompose" the segments into right triangles that have vertical and horizontal legs.

Measure the horizontal and vertical components of the segments.

Easiest to list them vertically in a table start at t = 0, 1, 2, etc.... and plot the distances versus time.

If it worked you should see that the horizontal distance for the parabola remains relatively constant (as does the dropped ball) while the vertical distance for BOTH increases in proportion to the square of the the time segment. (d = k t^2 where k is some "unknown" constant)

Note that the vertical distances will not be the SAME in both because the straight drop started at rest and the other one "rolled" of a ramp (it had an initial vertical velocity)

The distance being proportionate to the square of the time should be sufficient, but if that isn't acceptable for your proof, do the parabolic picture over, but this time roll it off a horizontal surface (like the table top). Doing this will not give it an initial vertical velocity. It should then very closely  "match" the dropped ball scenario.

Hope I am making sense. It's a bit tricky without drawing pictures.

Best of luck, you've set up a great experiment.