CH1 LESSON 1
Basics & Measurements
• Physical Units :
All physical quantities consist of two parts
(Numerical value & a unit)
• Example:
The average mass of a man is 60 Kg
( 60 is a numerical value & Kg is a unit )
Mr. Omar Ahmed
Measurements
Simply they are the basic physical quantities that all other
Physical quantities are related to these three quantities:
Length
Time
Mass & Weight
1-Length
unit : km , m , cm , mm
• Devices used to measure distance :
➢
➢
➢
➢
Ruler
Meter ruler
Measuring tape
micrometer
Mr. Omar Ahmed
➢micrometer
•
Measuring length and Thickness
Length can be measured with a ruler to the nearest 1 mm.
But when very small objects are used; we need to take measurements to the nearest 0.01 mm the
micrometer screw gauge makes this possible.
▪ Zero error :
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Is the reading displayed when you know the true reading should be exactly zero .
e.g. the zero error is the reading that shows when the calipers are fully closed .
The solution : subtract the value of the error from the measured value .
Example:
The reading starts with 2.5 cm & end with 6.5
So the length = 6.5 – 2.5 = 4 cm
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Important Precaution in measuring lengths
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Ruler must be close to the objects to be measured.
Eye must be vertically above the ruler while reading to avoid parallax.
Repeat your measuring several times and take the average.
When you use the measuring tape avoid bends in the tape.
Mr. Omar Ahmed
2-Time
unit : Sec , Min , Hour
Things used to measure time :
1- clock
2- stop watch
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Explain how you would measure a simple pendulum’s
Time period of oscillations.
1- use a stop watch
2- measure the time taken for
20 complete oscillations
• 3- Time for one oscillation =
total time
total number of oscillations
Mr. Omar Ahmed
3-Mass & Weight
unit : g , kg & newton
-Mass (Sensitive balance)
Mass is a measure of the amount
of matter in an object.
-Weight (Spring balance)
•Precautions in measuring mass:
• Balance should be
1.
2.
3.
Clean and dry.
Horizontal surface.
Adjusted to zero.
Weight: is calculated by the formula
Weight = Mass × g
g : acceleration due
to gravity = 9.8
Weight = Mass × 9.8 (on earth)
"When an object is moved from Earth to any planet with a smaller
gravitational strength, its mass remains the same,
but its weight changes based on the gravitational field strength (gravity)."
Volume
• An important physical quantity that is related to length is
the volume.
• Unit : 𝑴𝟑 & 𝑪𝑴𝟑
• Measuring volume of liquids :
They are measured using Measuring cylinders
•Important Precaution for using measuring cylinders
• Put measuring cylinder on horizontal surface to avoid tilting.
• Your eye should be perpendicular to the scale to avoid error
by parallax.
• Take your reading from the bottom of the meniscus.
Mr. Omar Ahmed
Volume - regular Shaped object
V cube = L × W × h = A × h
V cylinder = 𝜋 𝑟 2 ℎ
V sphere = 4Τ3 𝜋 𝑟 3
Volume – Irregular Shape object
V
object
= V2 - V1
Mr. Omar Ahmed
Density
• Density is the amount of material in unite volume
Or it is the mass per unit volume
Example 2
“Determining the Density of an Irregular Solid
Using the Water Displacement Method”
Aim
Find the density of an irregular solid
(e.g., a small stone) using a measuring cylinder.
Equipment
•Digital balance (±0.1 g)
•Measuring cylinder (100 𝒄𝒎𝟑 )
•Water
•Thread (if needed to lower the object)
Procedure
1.Measure mass (m): Place the dry stone on the balance. Example reading: m = 32.8 g.
2.Record initial water level (V₁): Pour water into the cylinder. Example: V₁ = 50.0 𝒄𝒎𝟑 .
3.Submerge the stone: Gently lower it into the water (no splashing, no air bubbles).
Record the new level, V₂. Example: V₂ = 62.5 𝒄𝒎𝟑 .
4.Compute volume of the stone:
0
