GoalExplain the sequence observation, hypothesis, experiment, conclusion; know simple measuring instruments and what they are for.
New words
hypothesis (a tested guess) · gipotezaexperiment · eksperimentmeasuring instrument · o‘lchov asbobiconclusion · xulosa
Explanation
We get our first knowledge of the world around us by observing phenomena. For example, people have long observed bodies falling to the ground and asked “what does the speed of falling depend on?”. Aristotle claimed that the heavier a body is, the faster it falls. While thinking, a guess about the cause of the phenomenon appears — a hypothesis. To test a hypothesis a special trial — an experiment — is carried out: besides observing, measurements are taken. According to legend, Galileo dropped a light and a heavy ball together from the Leaning Tower of Pisa, showed that they hit the ground almost at the same time and so disproved Aristotle’s idea. So the sequence of physical knowledge is: observation → hypothesis → experiment → conclusion. Experiments need measuring instruments: ruler, tape measure, vernier caliper (thickness and gap width), measuring cylinder (volume of liquid), balance (mass), stopwatch (time), thermometer (temperature).
Worked examples
Observation: wet laundry dries fast in the sun. Hypothesis: it dries faster in a warmer place. Experiment: two identical wet cloths — one in the sun, one in the shade; the drying time is measured. Conclusion: the one in the sun dries faster.
If a sheet of paper and a ball made by crumpling it are dropped from the same height, the ball lands first — because of air resistance. In a vacuum (no air) a feather and a hammer fall in the same way: in 1971 an astronaut showed this on the Moon.
Class activity
“Falling objects”: (1) a sheet of paper and a ball crumpled from an identical sheet, (2) a sheet placed on a book and dropped together. Observe, form a hypothesis and write a conclusion. Safety: drop from no more than 1.5–2 m and keep the landing area clear. Extra: healthy students count their heartbeats in 1 minute (at rest about 70–100 beats), then again after light exercise.
Practice
1
What is meant by a hypothesis?
A guess about the cause or law of a phenomenon; it is tested in an experiment.
2
How does observation differ from an experiment?
In observation we do not influence the phenomenon; in an experiment we choose the conditions and take measurements.
3
Which instrument measures the volume of a liquid and which the thickness of a pencil?