Unit 1: Making Measurements and Time - PHYSICS S3B

Unit 1 of Physics IGCSE S3B

TB DEFINITION: Mass is the quantity (amount) of matter a substance is made of. It is the quantity of matter a body is composed of; mass causes the object to resist changes in its motion and causes it to have a gravitational attraction for other objects.

Mass is how much matter a substance is made up of.

What is mass?

Kilograms (kg).

What is the SI unit for mass?

TB DEFINITION: Volume is the space occupied by an object.

Volume is the amount of space that a substance or object occupies, or that is enclosed within a container.

It is the space a substance takes up.

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ADDITIONAL INFO:

Volume Formulas for Regular Objects:

SQUARE: s³

RECTANGLE: lwh

SPHERE: 4/3πr³

CONE: 1/3πr²h

CYLINDER: πr²h

What is volume?

m³ (cubic metre).

What is the SI unit for volume?

Density tells us how concentrated its mass is of a substance. It is a property of a substance. It is the ratio of mass to volume for a substance.

Density is also known as the mass per unit volume for a substance.

It is calculated a s p = m/v (p is the Greek letter rho in this instance.)

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ADDITIONAL INFO:

• Gases have much lower densities than solids or liquids.

• An object that is less dense than water will float on water.

• Denser liquids that are immiscible (do not mix) will sink under less dense liquids.

What is density?

kg/m³ (kg per cubic metre)

What is the SI unit for density?

One period is the time it takes for a pendulum to make one oscillation — which is a full swing from left to right and back again (LEFT→RIGHT→MIDDLE = 1 OSCILLATION)

What is one period?

The International System of Units. (or in French: Le Systeme International d’Unites)

What does the SI System stand for?

Metres (m).

What is the SI unit for length?

Measuring with a Vernier Caliper:

Measured length at Main Scale (usually in cm/inches) + measured length in Vernier Scale (usually in mm)

→ Line up the object between the jaws of the vernier caliper (either measuring external or internal dimension) and get the measurement of the object before the zero mark on the vernier scale. Starting from the zero going to the right, on the vernier scale, find a line that aligns PERFECTLY with the corresponding line on the main scale. That line would be 0.1x of the main scale. Add the two measurements together to find the TOTAL measurement.

Eg. Main scale: 1.1cm Vernier scale: 0.2 cm. Total: 1.3 cm.

How do you measure lengths with a vernier caliper?

Measuring with a Micrometer/Screw Gauge:

Measured length at main scale (usually in mm) + measured length at circular scale (usually in 0.01mm)

→ Line up the object between the anvil and the spindle and get the measurement of the object at the main scale. Find the line that aligns perfectly with the horizontal number line of the main scale at the circular scale. This is your circular scale measurement (usually in 0.01x of the main scale, so 0.01mm). Add the two measurements together to get the total measurement!

Eg. Main scale = 12.5mm. Circular scale = 0.03mm. Total: 12.53mm.

How do you measure lengths with a micrometer/screw gauge?

Liquids can curve up or down in a container. Read the volume of the liquid as the BOTTOM of the MENISCUS. (Meniscus is the curved upper surface of a liquid).

How to read volume in a measuring cylinder?

Displacement Method:

If the irregularly shaped object is denser than water, you can fill a measuring cylinder with some water (not fully) and mark the volume of water. Then, immerse the object inside the water and record the current volume. The increase in volume is the volume of the object, as the volume of the displaced water is how much volume the object is made up of.

How do you measure the volume of an irregularly shaped object?

Accuracy: The measurement is close to the actual value when you compare it. (Your measurement VS real value, small variation)

Precision: When several readings are close together when measuring the same value. (Your measurements VS each other, minimum spread, small range)

Accuracy VS Precision

To improve length measurement accuracy, choose the correct tool for the scale, align the zero mark or a clear baseline properly, avoid parallax error by positioning your eye directly above the marking, and repeat measurements to calculate an average.

How to improve the accuracy of measuring lengths?

You can improve the accuracy by: using automated digital sensors like light gates to eliminate human reaction error, measuring multiple repeating cycles or oscillations to calculate an average, and syncing your clocks with precise national time standards or atomic references.

How to improve the accuracy of measuring time?

Measuring multiple oscillationsreduces human reaction error to find a highly accurate period.

EXTRA EXPLANATION:

• Human Reaction Time: Human reaction error is about 0.2 to 0.3 seconds.

• Error Dilution: Measuring 20 oscillations spreads your reaction error across the entire set.

• Math Example: If total reaction error is 0.2 seconds over 20 swings, the error per swing drops to just 0.01 seconds. (0.2/20)

• Averages Out Anomalies: It cancels minor variations caused by sudden drafts or slight release angles.

• Easier Tracking: It is visually much easier to count 20 continuous passes than to perfectly catch the exact microsecond a single swing reverses direction.

Why do we measure multiple oscillations rather than one oscillation in finding the period?

Weight is the downward force of gravity that acts on an object because of its mass.

What is weight?

SUMMARY:

• Length can be measured using a ruler.

• The period of one oscillation can be measured by measuring the time for 20 oscillations and then dividing the time by 20.

• The volume of a cube or cuboid can be found by measuring the length of the three sides and multiplying the measurements together.

• The volume of a liquid can be measured using a measuring cylinder where the bottom of the meniscus appears on the scale when looked at horizontally.

• All objects that sink in water displace their own volume of water.

• The volume of an irregularly shaped object can be found from the change in the height of liquid in a measuring cylinder when it is immersed in the liquid.

• Density is the ratio of mass to volume for a substance: p=m/v.

• The density of water is 1000kg/m³ or 1.0g/cm³.

• Anything less dense than water will float in water and anything denser than water will sink in water.

• Ice floats because it is less dense than water.

• One liquid will float on top of another liquid if it is less dense.

• Time can be measured using a clock or watch.

• An analogue clock has hands and can only measure time to the nearest second.

• A digital clock displays numbers and records time to a precision of at least one hundredth of a second.

UNIT 1 TEXTBOOK SUMMARY