Observations and results
In general, did the tub slip down the icy ramp better than the dry ramp? Was the smallest ramp angle needed for the tub to slip on the icy ramp smaller than the angle needed on the dry ramp?
When two objects rub together, there is always friction, and the surfaces of the two objects determine the amount that is generated. In this activity, you should have seen that there was less friction between the tub and the icy wood than from the dry plank. In other words, a smaller ramp angle was needed when using the icy wood than when using the dry wood for the tub to slip.
To calculate the force of friction, one must multiply the coefficient of friction by the force generated by the object, which was the mass of the tub in the pull of gravity. Although the mass of the tub and gravity did not change, the coefficient of friction of the two ramp systems did. The icy plank and the tub bottom had a lower coefficient of friction than the dry wood and the tub. You can easily feel this difference by carefully running your hand along the icy and then dry wood surfaces. The icy plank's frozen coating makes it much smoother than the dry wood.
More to explore
"Friction" from Kidipede, History and Science for Kids, Portland State University
"Moti" from Motion Basics: Friction from Rader's Physics4Kids.com
"Finding an Angle in a Right Angled Triangle" from Math is Fun Advanced
"Slip Sliding Away: Experimenting with Friction" from Science Buddies
This activity brought to you in partnership with Science Buddies