# 3.1 Observations and Measurement - PowerPoint PPT Presentation

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3.1 Observations and Measurement. You are constantly making observations—you hear a noisy motorcycle going by or you look at the clock and realise there is still 30 minutes to lunch. Just like you, scientists make observations about the world around them.

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3.1 Observations and Measurement

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### 3.1 Observations and Measurement

You are constantly making observations—you hear a noisy motorcycle going by or you look at theclock and realise there is still 30 minutes to lunch. Just like you, scientists make observations aboutthe world around them.

### Qualitative and quantitative observationsScientists can make two types of observations.

• Some observations are qualitative, being written down in words only. Qualitative observations would be made about the noise a bird makes, the taste of ice-cream or the fact that bubbles appear when the top of a soft drink bottle is unscrewed.

Other observations are quantitative. These observations involve measurements and are written as numbers. Examples would be the temperature of a room recorded as 25°C, a sprint timed as taking 12.3 seconds, or the volume of a liquid being measured as 375 mL.SeeHomework book 1.5 Observing and measuring.

Inferring and predicting.From your observations, you can make an inference, or logical explanation, about what happened and why it happened. You may then be able to predict how it could work in the future.

Mrs.Constande was sleeping when the alarm went off. She checked the alarm and started to yell, "Sarah hurry up! Get ready! We need to call Mrs. Cole and Mrs.Sani! Hurry! Get dressed!"

All of the students inferred that Mrs.Constande overslept because she set her alarm clock to the wrong time.

They also inferred that she was late for work.

Mrs.Sani came out holding a dog leash and yelling, "Hayden! Ferris! Did you leave the door open again? Oh no! Georgia! Georgia! Oh no!" and she began to cry. The students inferred that Mrs.Sani's dog had ran out of the house because her children left the door open.

Predictionsmust be logical and based on the observations made in your experiments. Every day you make observations, inferences and predictions, probably without even knowing it!

• Observation: The dog barked.

• Inference: The dog has heard something.

• Prediction: That possum is back again.

### Sometimes the same observation can lead to differentinferences and predictions:

• Observation: The leaves are turning brown.

• Inference: The tree is dying.

• Prediction: I will have to get a new one.

• or:

• Observation: The leaves are turning brown.

• Inference: It is a deciduous tree that loses its

• leaves in autumn.

• Prediction: It will get new leaves in spring.

• A calendar may assist you in deciding which is correct.

MeasurementMeasurements are extremely important in science. They improve the accuracy of your observations and allow you to see any patterns that may exist.

Scientists always use units from the metric system for their measurements. Gramis used for the measurements of small masses, like the masses of a coin or a mouse. Kilogram or tonne are used for heavier objects. Millimetres, centimetres, metres and kilometres are used for lengthMillilitres and litres are used to measure volume and seconds, minutesand hours for time.

Taking accurate measurements.A mistake is something that was silly and able to be avoided with care. Errors are not mistakes, but are slight changes in measurements that cannot be avoided, regardless of how careful you are. For example,your thermometer may be damagedor inaccurate.

### A common error is caused by not having your eye directly in line with the measurement. This is called parallax error.

Sometimes the measuring device gives us a zero error. This often happens when using a scale to weigh something. Even though it is empty, it might give us a small measurement.

To minimise errors, scientists need to follow theserules or conventions:• Reduce parallax error by always reading measuringdevices from directly in front.• Make sure there is no zero error by having themeasuring device at the correct starting point.• Always write down measurements as soon as theyare taken. Do not try to remember measurements.• Always measure quantities in metric units.• Always write down the units of the measurements.• Always use the correct abbreviations for units.• If possible, write all measurements in a table.

• Do not use fractions like 1⁄2 or 1⁄4 in measurements.

• Use decimals instead—9.5 kg is fine, whereas 91⁄2 kg is not.

• ***STOP! …. If you are working in a group, always make sure you have a copy of the results before you leave the laboratory.

### Have a go at completing Revision Questions on page 20.

• Revision questions

• Qualitative and quantitative observations

• 1 Are the following observations qualitative or

• quantitative?

• a The sunset was a brilliant red.

• b The car was travelling at 100 km/h.

• c The time was 10:45.

• d The dog barked.

• 2 Make four observations about samples of:

• a sugar d a \$1 coin

• b water e the gas we breathe out.

• c talcum powder

• Inferring and predicting

• 3 Separate these statements into observations, inferences

• and predictions.

• a The missing fish were eaten by the cat.

• There will be no fish left in the pond after a while.

• The cat is on the edge of the fishpond.

• b One Olympian is bigger than the other.

• The bigger Olympian will win the event.

• One will lift a heavier weight than the other.

• c The fish is a big one.

• I’ve caught a fish.

• The line is taut and the fishing rod is bending.

Now that you are familiar with most of the laboratory equipment(page 9 and 10 of Teachers text) and are confident at safely lighting the Bunsen (page 14 and 15 Teacher Text), then you are also ready to carry out your first practical investigation (page 15 Teacher Text) CONGRATULATIONS!!!! But remember, inferences, predictions, observations (qualitative and quantitative), measuring, errors and recording your observations in a table straight away, and gather any other group observations before you leave the laboratory. HAVE FUN !!!

HOW HOT IS HOT?This is your Science Prac for Week 3.You will needBunsen burner, bench mat, matches, safetyglasses, tripod, gauze, 250 mL beaker, stopwatchor clock with second markingsWhat to do1 Set up the equipment for boiling water as shown inFigure 1.2.10. Science Dimensions2 Using the markings on the beaker, add 100 mL oftap water.3 Time how long it takes for the water to boil when usinga blue Bunsen burner flame. Boiling will be obviouswhen the water begins to bubble vigorously.4 Allow the first beaker to cool completely or get a newbeaker.Warning: Never try to cool a hot beaker with cold water.5 Repeat the experiment with a yellow flame only. *****REMEMBER YOUR SAFETY RULES AND YOU WILL STAY SAFE.