Uniform Acceleration: Penny and Feather

Photo shows the demonstration used at the University of Texas at Austin.

Concepts Conveyed:

• In a vacuum, objects falling from the same height will reach the ground at the same time regardless of mass and shape.
• Under normal conditions, air resistance affects the rate at which the objects fall.

Instructions / Notes:

• Demonstration apparatus includes a plastic tube containing a penny and a feather at rest at one end of the 100 cm tube.
• Before creating the vacuum, quickly invert the tube to the opposite vertical alignment to demonstrate that the penny and feather fall at different rates.
• After the objects are at rest, connect the tube to the vacuum pump. It takes less than 1 minute to pump air out of the tube.
• Close the valve/petcock and disconnect the hose and repeat the inversion, as before, noting the difference in descent.

Vacuuming out the tube:

• Connect the red hose to the vacuum valve by tightening the clamp around the nozzle, as seen in the picture above.
• With the vacuum valve in the parallel open position, turn on the vacuum pump using the power switch. Leave pump running for about 30 seconds.
• Close the valve by moving it to a perpendicular closed position before turning off the pump and disconnecting the hose.
• To allow air back into the tube, return the valve to the open position.

Demo Staff:

• Clamp tube stand to table.
• OPEN VALVE: valve knob is PARALLEL to the vacuum hose and to the tube.
• CLOSED VALVE: valve knob is PERPENDICULAR to the vacuum hose and to the tube.
• Make sure to ask the instructor if they want the tube in vacuum prior to rolling out.

Last updated on November 7, 2024