# Lesson Notes By Weeks and Term - Senior Secondary 1

Density and relative density

Term: 1st Term

Week: 7

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject:      Physics

Topic:-       Density and relative density

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Define Density
2. Describe how to determine density
3. Define relative Density
4. Describe how to determine the Relative Density of Solids & Liquid

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher reviews the previous lesson on scalar and vector quantity Students pay attention STEP 2 EXPLANATION He defines density and describes how to determine it Students pay attention and participates STEP 3 DEMONSTRATION He defines relative density and describes how to determine it for solids and liquids Students pay attention and participate STEP 4 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

DENSITY AND RELATIVE DENSITY

The density of a substance is the mass per unit volume of the substance. Density = mass of a given substance

Volume of the substance

Density is scalar quantity& measured in kgm-3 (kilogram per cubic meter)

DETERMINATION OF DENSITY

The determination of density involves the determination of a mass and a volume. The mass can be found by weighing. The density of a substance can be determined using a graduated density bottle.

Relative Density

Relative density is also known as specific gravity. Relative density of a substance is defined as the density of the substance per density of water.

R.D = Density of the substance

Density of water

R.D is also equal to the ratio weight of a substance to weight of an equal volume of water. As weight is proportional to mass

R.D = mass of substance

Mass of equal volume of water

DETERMINATION OF R.D OF SOLID (E.G. SAND)

Mass of empty bottle = m1

Mass of bottle + sand = m2

Mass of bottle + sand + water = m3

Mass of bottle + water only= m4

Mass of sand = m2 – m1

Mass of water added to sand = m3 –m2

Mass of water filling the bottle = m4 – m1

Mass of water having the same volume as sand = (M4-M1) – (M3-M2)

Relative density =         Mass of sand

Mass of equal volume of water

R.D =          m2 – m1

(m4 - m1) - (m3 -m2)

DETERMINATION OF R.D OF LIQUID

Mass of empty density bottle = m1

Mass of bottle filled with water = m2

Mass of bottle filled with liquid = m3

R.D of liquid = m3 – m1

m2 – m1

Examples

A glass block of length 10cm width 8cm and thickness 2cm has a mass of 400g. Calculate the density of the glass.

Solution

l = 10cm = 0.1m, b = 8cm = 0.08cm, h = 2cm = 0.02m, m = 400g = 0.4kg

V = l x b x h = 0.1 x 0.08 x 0.02

= 0.00016m3

Density = Mass (m) = 0.4= 2500kgm3

Volume (V)              0.00016

Examples

Calculate the volume in m3 of a piece of wood of mass 500g and density 0.76gcm-3 Mass of the wood = 500g

Solution

Density = 0.76gcm-3

Volume =?

Volume = mass / density

1. 500

0.76

Volume = 658cm3 = 6.58 x 10-4 m3

Example 2

An empty relative density bottle has a mass of 15.0g. When completely filled with water, its mass is 39.0g. What will be its mass if completely filled with acid of relative density 1.20?

Solution

m1, mass of empty bottle = 15.0g

m2, mass of bottle + water = 39.0g

Mass of acid = n – 15.0g

Mass of water = 39.0 – 15.0g

= 24.0g

R.D = 1.20

R.D = n – 15.0g

39.0 – 15.0g

1.20 = n –15.0

24.0

n- 15.0= 1.20x24.0

n- 15= 28.8

n =28.8+15

n=43.8g

NOTE: The hydrometer is an instrument used to measure the relative density of liquids

EVALUATION:    1. Define density

1. What does it mean by the statement that the density of gold is 19.3gcm-3
2. Differentiate between density & relative density
3. A glass block of length 100cm width 60cm and thickness 20cm has a mass of 4000g. Calculate the density of the glass
4. 40 m3 of liquid P is mixed with 60m3 of another liquid Q. if the density of P and Q are 1.00kgm-3 and 1.6kgm-3 respectively. What is the density of the mixture?
5. The density of 400cm3 of palm oil was 0.9gcm-3 before frying. If the density of the oil was 0.6cm-3 after frying, assuming no loss of oil due to spilling, its new volume was?

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively