In this section we will observe 5 inelastic collisions of a small object dropping onto the IOLab device as it rolls. We will find the change of momentum, and the unknown mass for each collision.

Find a mass to drop onto your device. A ziplock bag of sugar or other grain, or cons, works very well.

It must be heavy enough to clearly change the momentum of the device, and light enough not to completely stop the device when it drops.

Because we reproduce inelastic collisions, the bag must not bounce or roll. You may use tape to make the mass stick when it drops.

This measurement will be used to determine the mass of the object from the conservation of momentum equation.

The first trial runs will be for you to observe how it works and think about how to take better data.

Select the Wheel velocity sensor in the software, and press record.

Push the IOLab device to start it rolling.

Drop (DO NOT THROW!) your mass onto the device.

Watch that the mass only falls: if it has any horizontal momentum it will skew your results. This requires coordination and may require practice!

Examine your velocity plot. Identify where in the plot the push and the collision occur.

If you cannot identify where the collision occurs, you may need to use a heavier mass, or practice dropping the mass vertically without any horizontal motion.

Write a list of where you think the most energy loss and other error comes from in this experiment. Indicate what you can do to minimize these. Keep the list for your results.

• The momentum of the system after collision is

• mvf=(md+mu)vf,

• where vf is the final velocity of the combined mass, mu is unknown mass of the object, and md is mass of the device.

• Calculate the unknown mass mu using conservation of momentum for the inelastic collision of the system:

• mdvdi= mvf , which can be rewritten as mdvdi=(md+mu)vf

The above is the speed change after the weight is applied

The mass of the device is 0.2kg

Make a table for each collision, with columns for momentum before, momentum after, the unknown mass calculation, and percent error. Weigh the unknown mass.

Calculate percent error of the mass of the object using the 5 trials (equation from overview section).

Use the mass found by weighting as your more accurate result (A), and compare with the masses calculated using conservation of momentum (x).

Wheel - Velocity (100 Hz) 1.0 t: 3.2495 s X: -0.979 m/s At: 0.54000 s u: 0.187 m/s 0: 0.061 m/s a: 0.101 m s: -0.32 m/s2 (r2: 0.73) 0.8 0.6 0.4 (s/w)^ 0.2 -0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 Time (s) Wheel - Velocity (100 Hz) 1.0 t: 3.2495 s X: -0.979 m/s At: 0.54000 s u: 0.187 m/s 0: 0.061 m/s a: 0.101 m s: -0.32 m/s2 (r2: 0.73) 0.8 0.6 0.4 (s/w)^ 0.2 -0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 Time (s)