# 10 October Science 7 Free fall and partner tree

Today we will try to gather data on the free fall of a lump of clay from the outer stairs. We will need full cooperation of the class–good observations–timers and videographers, complete recording of the data, full attention. Safety is paramount.

We will distill the time data using medians of the timers (5), and medians of the trials. We will graph the heights (distances) from where the clay ball is dropped and these median times for the descent.

We will see what our graph looks like and discuss what the ideas of Galileo and Newton predict.

If we get “nice” data, I will show those interested a graphical technique for determining instantaneous speeds. With instantaneous speeds it is possible to determine the rate of acceleration. (Acceleration cannot be determined with averages speeds. Average speeds, however, can give you a sense that the speed is changing.) Data from all classes will be made available for comparison purposes.

Before we begin, make sure you have drawn an expectation sketch graph. Explain your thinking.

Why is gravity considered a force?

When Newton was asked what gravity “is,” he responded, “Hypotheses non fingo.” (LatinĀ for “I feign no hypotheses,” “I frame no hypotheses,” or “I contrive no hypotheses”–from the Wikipedia entry.) What do you think he meant?

Gravity is an example of a force that acts across a distance with no visible material connection between attracted objects (there is no “string” between the earth and the moon, for example). What ideas can you imagine that would explain the way two objects can be attracted to each other without being connected by something material? (This is one of the things that bothered Einstein, who developed a physics of motion based on different assumptions about space and time from Newton. Einstein’s system can incorporate Newton’s ideas as well as more general predictions fromĀ the very large, the very small, and the very fast. If you are interested in Einstein’s ideas, see me and I can recommend some resources.

Period 8 (median of the median times for each height):

• 9.0 m — 1.16 sec
• 8.5 m — 1.07 sec
• 5.3 m — .85 sec
• 4.6 m – .75 sec
• 2.3 m .48 sec

Period 8 clay ball drop from outer stairs

Of interest:

http://physics.info/falling/

http://www.ck12.org/physical-science/Acceleration-Due-to-Gravity-in-Physical-Science/