Rolling vs. sliding kinetic energy changes

Goal: Determine whether rolling bodies and bodies sliding down the same frictionless slope will accelerate at different rates.

Concept: Objects with different moments of inertia but the same mass will have the same sliding acceleration but different rolling accelerations, since some of the potential energy of the "falling" object will be used to turn the object. Take a look at the discussion on Rolling Bodies to get an idea of how you might set up this experiment.

Materials

• Inclined plane with frictionless (or nearly so) surface: metal, glass, or teflon.
• Two solid cylinders, two hollow cylinders, balls with same diameter. You may be able to find something that will work at a local hardware store. They should be as smooth as possible to reduce friction, and should have the same mass if at all possible. [The metal and wooden balls in the kit have the same diameters.]
• Stopwatch

Procedure

1. Find the moments of inertia (from a table) for each type of object. Which objects should take the longest to roll down the incline: solid cylindar, hollow cylindar, or ball?
2. Set up two slopes or a single slope wide enough to accommodate a pair of cylinders.
3. Using the solid cylinders, slide one and roll one down the plane. Using the timer, note the length of time it takes each cylinder to reach the bottom of your slope.
4. Using the hollow cylinders, repeat the experiment.

Data Handling

1. Lay out your data in tables with the records of your actual data (length of slope, mass and shape of object, duration of travel down slope.
2. Add a column to calculate acceleration from your data.
3. Add a colume to calculate acceleration based on the slope and gravitational acceleration, assuming no friction.
4. Determine the coefficient of friction.

Report

Compare your predictions (based on the formulae for the moments of inertia) with your data for each shape used, and propose explanations for any deviations.

Post your report to the Lab assignment at the Moodle.

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