K-O Physics

Friction Forces

The object of the lab is to measure the coefficient of friction between different objects.

Procedure:

If necessary, zero the scale when it is horizontal by sliding the face of the scale until the pointer registers zero.  Drag the object at a slow, constant speed and record the force for static and kinetic friction.  Do this when the object is loaded with masses starting at 1000g, going up in 500g increments to a maximum of 3000g.  Repeat this experiment with two other surfaces.  You max out the scales when approaching 3000g, so modify your increments accordingly.

Analysis:

Draw graphs of friction force versus normal force (for each surface) on Excel and determine the slope of the resulting trend lines (for static and kinetic friction).  Draw a free-body diagram of the situation.

• What did you measure that is equal to the friction force?
• What is the slope of the line equal to and what does it represent?
• When you pulled on the scale to start the block moving, why did the scale reading drop quickly when the block started to move?

Use these questions as a guideline for your conclusion and error analysis.

Due Date: Tuesday, November 10th

***Please record your data in an excel document and send it to me.  We need to compile the class data.***

Rockets lab: 2-D Motion

Theory:

For sufficiently dense falling objects (dense enough to render air resistance negligible), the Earth’s gravitational field provides a constant acceleration of 9.81 m/s2 at the surface of the Earth.  Using an air-propelled rocket, we will assume that there is minimal air resistance, allowing the constant acceleration kinematics equation to work for the experiment,
y = yo + vot + 1/2 at^2

where y is the position at any time t,  while yo and vo are the initial position and velocity in the y-direction, and a is the acceleration in the y-direction, which will be g = 9.81 m/s^2 for this experiment.  This equation is sufficient to understand free-fall, since all of the motion is in the y-direction.  However, for a projectile launched at an angle to the horizontal, we must also analyze the motion in the x-direction.  Fortunately, the two motions are independent on each other.  Thus we can measure the motion in each direction separately.  Since there is no acceleration in the x-direction (if we ignore air resistance), the kinematics equation in the x-direction is given by the following equation.

x = xo + vot

Using these two equations we will be able to determine the peak height of rockets shot at various heights and at various speeds.

Experiment:

Using a stopwatch to measure flight time and a device to measure range, fire the rockets to determine the peak height of the rocket at different angles.  Additionally the initial and final velocities of the rocket can be determined.  The rockets can also be fired at different power levels, so data can be obtained for the low, medium, high, and super settings.

Note that the higher the power setting you use, the more air resistance will factor into your results.  As a result, the lower power settings, although not as much fun, should produce better results.  In order to determine the above information, you must assume that air resistance is negligible and that there is a constant acceleration of gravity, g.

After acquiring all of the data at the five different angles, compile the data and make conclusions about the findings of the class.  As always, a discussion of the possible errors that occurred in necessary.

Due Date: Tuesday, October 20th

Remember to use g = 9.81 m/s^2 in labs.