Inertia

brief summary of topics discussed:

(time 0:00) examples of motion in nature - waterfall, waves, wind etc; Purcell in his easy chair discussing ho it is the job of physics to explain motion

(1:15) slide book along table, need to simplify system, eg to get rid of friction

(2:18) dry ice puck on glass

(4:40) push disk (=puck), also bolw on disk with straw to accelerate; 2 questions to ask: what happens during the push? what happens when the disk moves by itself?

(6:00) scale set up beside glass table

straight line motion of disk demonstrated

(7:40) photo of free motion (Purcell refers to film notes where all photos appear to allow students to analyze data)

calipers used to compare distance travelled in each interval, approx 16 cm

(9:20) "if a body moves free from disturbing pushes and pulls it moves in a straight line at a constant speed"

(11:00) "an object on which no unbalanced force acts moves with a constant velocity"

motion with an unbalanced force

(11:45) rubber ring attached to disk, ring is distorted when pulled, use shape of ring to establish that a constant force acts on the disk

difficult to apply a constant force by hand, so use a "trained assistant"

(13:40)motion under an unbalanced force, flash photo, chech distortion of rubber ring - force was constant

(15:00) use pieces of tape to compare distance travelled in equal time intervals, cut tape and paste on board to create a v vs t graph (4 intervals)

(17:48) effect of magnitude of the force, use 2 rubber rings, in parallel, stretched the ame amoun as in previous experiment

(18:39) photo of motion, suggests viewers d careful analysis, Purcell compares the distances travelled in 2 consective intervals, compares deltav for 2f is twice deltav for f

(21:00) "for a given object subject to an unbalanced force, the acceleration is proportional to the force"

(21:20) 2 forces acting in different directions (60 degrees apart), analysis not performed, refers to film notes

(22:40) introduces "assistant" - a second disk on sloped table

(23:15) back to office - summary

(24:00) quote from Galileo

(24:50) "inertia"

(25:26) what happens if we apply forces to a different body? - subject of next film

(25:40) credits