Frictional Force on ball rolling down incline

[Alex22]

Hi everyone,

For an experiment I wanted to investigate the forces acting on a ball when rolling down an incline. Basically I have a wooden incline with a photogate at the bottom to measure the velocity of the ball at the bottom of the ramp.

At the top of ramp the sphere has potential energy mgh. When the ball is released (without any initial speed) it rolls down the incline and through the photogate. Seeing as the photogate is not perfectly on floor level there is still some potential energy. Yet the difference in potential energy should be equal to the gain in kinetic energy (linear and rotational) minus any work done?

In the experiment I altered the height of the ramp and measured the velocity. Yet when attempting to plot a graph of the frictional force (work done/distance traveled by ball) against the normal force (cos theta m g ) I get a very weird line of best fit, with a gradient of around -0.5. If the key force is rolling friction we would expect a positive gradient seeing as the frictional force is normal force multiplied by the coefficient of rolling friction.

Is there some error in my method, some principle I oversaw or are the forces so negligible?

Thanks!

Alex

 

[Dr. Courtney]

Do you mean the kinetic energy exceeds the initial potential energy?

 

[Alex22]

Not necessarily, its more of a problem trying to figure out the relationship. I'm stuck on what I should graph for the investigation. GPE and Work Done/Friction correlate positively, yet I can't make much sense of the correlation between the normal and frictional force.

 

[Chestermiller]

Not necessarily, its more of a problem trying to figure out the relationship. I'm stuck on what I should graph for the investigation. GPE and Work Done/Friction correlate positively, yet I can't make much sense of the correlation between the normal and frictional force.

Show us your analysis, and maybe we can help you.

Chet