Editing Free Falling (section)

== Demonstration ==

# Show the feather and small stone to the students. Ask them to point at the one that will fall faster (The small stone). Show that the stone does fall faster, and ask for ideas on why that is.
# Explain that air resistance is the key factor, and that gravity is a constant acceleration. Pull off the top end of the gravity tube and place the feather in one of the compartments, and the stone in the other. Put the top end back on snugly.
# Attach the vacuum pump to the gravity tube. Open the valve on the tube and turn on the vacuum pump. You may need to hold the hose on the valve to ensure a good connection, and after 20-30 seconds close the valve. Turn off the vacuum and explain that there should now be only a small amount of air in the gravity tube.
# Rotate the knob on the top end to have the feather and stone drop. They should fall at the same speed or close to the same speed! Ask the students for ideas on why the feather fell faster this time compared to when you dropped it.
# If students would like to see it again, you can pick up and flip the tube slowly to have the feather and stone return to the top. Have someone help you by spinning the knob to get the objects back in the compartments.