“We must trust to nothing but facts: These are presented to us by Nature, and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation.” ― Antoine Lavoisier, Elements of Chemistry

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## Saturday, 29 November 2014

### Slides: Kinetic Theory of Particle Presentation (ppt)

Here are the slides of Particulate of Matter (Kinetic Theory of Particle)

Link to download : Particulate of Matter - part 1

Particulate of Matter - part2

### TURNING ON A PIVOT worksheet (ANSWER)

1. Calculate the moment of this force. Show your working.

Moment = F x D
= 100N  x  0.3m
= 30Nm

2.   This system is balanced
a)      Calculate the size of the clockwise moment
Clockwise moment    = (20N x 3m)  +  (25N x (3m + 1m))
= 60 Nm  + 100 Nm
= 160 Nm

b)      State the size of the anticlockwise moment
Anti-clockwise moment        = X N  x 2m
= 2X m

c)      Calculate the size of force X
Clockwise moment    =  Anti-clockwise moment
160 Nm      =  2X m
160 : 2 = X
80 = X

3.  A pivoted uniform bar is in equilibrium under the action of the forces shown.
What is the magnitude of the force F?
Anti -Clockwise moment  =  Clockwise moment
10N  x  4m                    =  (F x 2m) + (6N x (2m+2m))
40 Nm   =  2F m + 24 Nm
40 Nm – 24 Nm    = 2F m
16 Nm         = 2F m
16 Nm : 2 m              = F
8 N      = F

4.   A uniform beam AB of mass 20kg and length 3m rests in equilibrium in a horizontal position. The beam is supported by a single pivot at C and a particle of mass 6kg is attached at B.

Calculate the distance AC.
Assume:    AC is X meter, so CB is (3 – X) meter
Anti -Clockwise moment  =  Clockwise moment
20 kg  x  X                    =  6 kg  x  (3 – X)
20X                    = 18 – 6X
20X + 6X           = 18
26X        = 18
X        = 18 : 26
X        = 0.69 meter

5.    a uniform metre rule, freely pivoted at a point 20 cm from end P.

The rule is kept horizontal by means of a 120g mass suspended 5.0 cm from end P. Use the principle of moments to help you determine the mass of the metre rule.
Anti -Clockwise moment  =  Clockwise moment
120 x 15                        =  MASS x 30
1800                 = MASS x 30
1800 : 30          = MASS

60 gram            = MASS

6.   Look at this example of a balanced system

a)      Calculate the size of the clockwise moment
Clockwise  Moment = F x D
= 10N  x  4.5m
= 45Nm

b)      State the size of the anticlockwise moment
Anti-clockwise  Moment       = F x D
= 15N  x  Xm
= 15XNm

c)      Calculate the distance x.
Clockwise moment      = Anti-clockwise moment
10N  x  4.5m =  15N  x  Xm
45 Nm = 15X Nm
X = 45 : 15
X = 3 m

## Tuesday, 25 November 2014

### WORKSHEET expansion

EXPANSION GRAPHS
http://www.4shared.com/rar/6mPL_1zsce/Documents.html

## Thursday, 13 November 2014

### PHYSICS: Moment worksheet

1. The diagram shows the electromagnet just above an iron rod, which is pivoted at one end. A box is hanging from the other end.

Ignore the mass of the rod in the following questions.

a) What is the mass of the box?
b) What is the force produced by the electromagnet?

2.   A beam of wood is balanced on a brick. A girl  stands at a point 50 cm from the centre. Ten 2 kg masses are placed on the plank 2.5 m from  the centre on the opposite side and the beam balances. What is the mass of the girl?

3. Henry uses the light seesaw shown below to measure Mary's mass.

Use the information in the diagram to calculate Mary's mass. Show your working.

4. An empty wheelbarrow, which weighs 65.5 N. The operator pulls upwards on the handles with a force of 20 N to keep the handles horizontal. The point marked M is the centre of mass of the wheelbarrow.

Determine: the distance between points A and M.

### Review: Acids and Bases for Checkpoint

Acids
¢  An acid is a compound/substance that produces hydrogen ions (H+) when dissolved in water
¢  Acids taste sour.
¢  Acids turn indicators red
¢  An acid has pH lower than 7

Bases
¢  Bases are ionic compounds that produce hydroxide ions (OH-) when dissolved in water .
¢  Bases taste bitter and feel slippery
¢  Bases turn indicators blue
¢  Bases release hydroxide ions in water solutions (the more released, the stronger the base)
¢  Has pH more than 7; pH range  7-14

Indicators
¢  Indicators are weak organic acids or bases which have the property of changing color in solution when the hydrogen ion concentration reaches a definite value.
¢  The most used indicator is litmus (extracted from lichens)
¢  Blue paper litmus changes color to red in acid solution
¢  Red paper litmus turns blue in alkali solution
Acids Affect Indicators, by changing their color

Blue litmus paper turns  red  in contact with an acid  (and red paper stays red).

Bases Affect Indicators
Red litmus paper turns  blue  in contact with a base (and blue paper stays blue).
Phenolphthalein turns purple in a base.
The pH scale
¢  The pH scale is a measure of the hydrogen ion concentration, the scale runs from 0 to 14
¢  Acids have pH less than 7, more strength acid, the lower the pH
¢  Neutral substances have a pH of 7
¢  Bases have pH 7 to 14, more alkaline in solution, the higher the pH
¢  The pH of a solution can be measured by universal indicator paper and pH meter

More on pH
¢  If you add an acid to water, the concentration of hydrogen ions increases and the concentration of hydroxide decreases.
¢  The lower the pH value, the greater the hydrogen ion concentration.
¢  If you add base to water the concentration of hydroxide increases and the hydrogen ion concentration decreases.

¢  The higher the pH value, the lower the hydrogen ion concentration.

Common Acids and Bases

Acids
¢  Hydrochloric acid   HCl
¢  Nitric acid                            HNO3
¢  Sulphuric acid                    H2SO4
Bases
¢  Sodium hydroxide   NaOH
¢  Calcium hydroxide Ca(OH)2
¢  Magnesium hydroxide   Mg(OH)2
¢  Ammonium hydroxide  NH4OH

WORKSHEET

1.       Name 2 acids and their uses.

2.       Name 2 bases and their uses.

3.       Describe one way you can safely determine whether an unknown solution is an acid or base?

4.     How can an acid be neutralized?

## Tuesday, 11 November 2014

### Experiment: The Effect of Sulfur Dioxide (IGCSE class)

Guide Questions:

1. What are the sources of sulfur dioxide gas?
2. Describe the effect of sulfur dioxide to our environment?