1.3c Free fall and motion graphsWe Are Learning To •Acceleration due to gravity, g; detailed experimental methods ofmeasuring g are not required. •T erminal speed. •Represen tation by graphical methods of uniform and non-uniform accelera tion; interpreta tion of velocity-time and displacement-time graphs for uniform and nonuniform acceleration; significance ofareas and gradients.
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Note: Ask students what will happen when you drop two tennis balls. Both hit thefloor as expected. Then pass the tennisballs to a student. One is heavier than theother. One tennis ball has been filled withwater. This will challenge their thinking
Note: Stand on a desk and ask students to observe which object hitsthe ground first, (1) two oranges (2) an orange and a grape. The orangeand the grape should hit the ground at the same time.
Misconception: heavier objects fall faster than lighter objects.
Note: get two pieces of paper, crumple up the one piece and then drop themboth at the same time. The crumpled up paper hits the floor first eventhough its got the same mass as the other! Why?
Note: Cut out a circular piece of paper slightly smaller than a real coin. Dropthem both and the coin will hit the floor first (the air resistance on the coin
takes longer to build up, so it reaches a higher terminal velocity). Then drop thecoin and the paper coin together (paper coin above real coin), they both hit theground at the same time. Why?
Note: Invert the tube containing the coin and feather (with air in first).Then use the vacuum pump to extract the air. Invert again and thefeather falls at the same rate as the coin.
Note: Put a 1 kg mass onto a analogue weighing scale and then jumpoff a table holding the scales. Choose a weight to give a significantdeflection of the needle. Students observe the dial on the scale as
you fall with it. The dial should move anti-clockwise throughout thefall.
Safety: Take care jumping off the table (do not allow a student to
jump off the table). Make sure that the weight and pan is securedto the balance.
Note: The sound toy has a box inside that makes a noisein the tube as the box falls inside the tube. Stand on atable and jump off carefully as you invert the toy.Observe the noise of the toy as the teacher falls.
Safety: Take care jumping off the table (do not allow astudent to jump off the table).
Note: Fill a bottle (with a small hole in theside) with water. Observe the stream ofwater coming out of the bottle as thebottle is dropped into a dustbin.