## Sunday, 5 August 2018

## Sunday, 29 July 2018

## Liquid expansion: Real and apparent expansion, cubic expansivity.

Like solid, liquid expands on heating and contracts on
cooling, because liquid is always held in a container, the expansion of liquid
is always complicated because of the expansion of the container itself.

## Monday, 23 July 2018

## Friday, 6 July 2018

## Principles of Expansion: Advantages,Bimetallic strip, Uses in Electric iron, Fire alarm and thermostat

**Expansion of objects**

**The expansion of an object is the process of increasing in size, amount or number. It is relative, when we tall about expansivity.**

## Sunday, 30 July 2017

## Physics: static electricity, electric charges and law of charges.

##
**What is electricity?**

The is a form of energy that occurs when electrons flows through a conductor.### Areas Covered

- Definition of static electricity
- Nature of atoms of static electricity
- Electricity charges
- Law of charges
- Conductor and insulator

### Definition of static electricity

Static electricity is produced by the friction between two materials. For example, when rod is rubbed with silk.

## Sunday, 26 March 2017

## Physics: Introduction to radioactivity,types and properties.

It is a spontaneous emission of radiation from a substance usually an unstable .This process is also known as nuclear or radioactive decay).
In the year 1896, Henri Becquerel a French scientist working with phosphorescent materials discovered that a uranium compound placed on a
photographic plate which was covered with light black paper causing the plate to
be exposed by blackening the pate itself. This implied that some sort of radiation was coming from the
uranium which could pass through. The material was radioactive given-off
radiation. Other scientists that researched on radioactivity were;v This radioactivity was spontaneous with the radiation being omitted
without anything causing it apparently.

###
Types of radioactivity

From several experiments that have been carried out, it has
shown that there are three different types of radioactive emission called;

**Alpha particles ;**whose emission is easily stopped by paper or thick card

**Beta particles ;**whose emission is easily stopped by aluminium sheet of different thickness and are negatively charged.

####
Properties of alpha particles

1) Alpha rays are deflected by magnetic field.

2)
The direction of deflection of alpha rays shows
that they are positively charged

3)
They are relatively massive and so have more
momentum and tend to continue in their direction of travel.

4)
Alpha particles are absorbed by paper and air
and are easily stopped aluminium thin sheet.

5)
They have little penetrating power, travelling
no more than 5cm. Being large, it is soon stopped by air molecules.

6)
They are capable of stripping electrons from
their atoms because alpha particles have comparatively large mass and momentum.

####
Properties of beta particles

1)
There are also deflected by magnetic field but
in the opposite direction to alpha particles.

2)
The direction of deflection of beta rays shows
that they are negatively charged with –e .

3)
They are relatively light and as a result easily
deflected.

4)
They are deflected by different amount showing
that they have varying speed..

5)
They have good penetrating power of about 1
metre.

6)
They can penetrate a few millimetre of
aluminium.

7)
They produce less ionisation in air than alpha
particles.

####

####
Properties of gamma rays

1)
They are electromagnetic waves similar to light
wave but of very short wavelength.

2)
They are electrically uncharged since they are
not deflected by a magnetic field.

3)
They are highly penetrative compared to the
other two types and can only be stopped by thick lead blocks.

4)
They have high penetrating power compared to the
other two types.

5)
They have much less ionisation than alpha rays.

## Sunday, 12 March 2017

## Friday, 7 October 2016

## Physics: Equations of Motion, derivation, Questions and solutions

In my last article, The definition and types of Motion were discussed. Now this is an article to better understand Equations of motion with several questions solved.

**Related Terms**

**Displacement:**It is the distance moved in a specified direction. It is a vector quantity.**Distance:**It is the magnitude of separation between two points. It is a scalar quantity.**Speed:**It is the rate of change of distance with time. It is a scalar quantity.**Velocity:**It is the rate of change of displacement with time. It is a vector quantity.

**Acceleration:**It is the increasing rate of change of velocity with time. It is a vector quantity.**Retardation:**It is the decreasing rate of change of velocity with time.

**Equations of motion**

1)

3)

4)

**Derivation**

**Average speed = s/t**

(V+u)/2 =s/t

where, V =final velocity

U = Initial velocity

S = Distance

T = time

Make "s" subject of the formula.

..........(1)

Average acceleration= change in Velocity/time

a = (v-u)/t

at = (v-u)

V = U + at ...........(2)

Substitute (2) in (1)

S =[ (u + at +u)/2]t.

S =[(2u+at)/2]t

........(3)

From (2)

V = u + at

t =(v-u)/a

Substitute the value of t in (1)

S = (v+u)/2 x (v-u)/a

.....(4)

**Question 1**:

A car travels with a uniform velocity of 30m/s for 5s and then comes to a rest in the next 10s with a uniform deceleration.

Find,

a) deceleration

b) total distance travelled.

Solution,

a) using, V = u + at

Deceleration= -a

0 = 30m/s - a(10)

10a = 30

a = 3m/s/s

b) Let, "Stage A" be the period before deceleration.

"Stage B" be the period after deceleration.

At Stage A,

U= 30m/s

t1= 5s

S1= Distance travelled at stage A ?

Using,

From the V-T graph,

Initial Velocity (U) = S1/T1

S1 = ( 30 x 5) m

S1 = 150 m

At Stage B,

U= 30 m/s

V = 0

T2 = 10s

S2 = Distance travelled at stage B ?

Using,

0 = (30)(30) + 2(-3)(s2)

900 = 6(s2)

S2 =150m

Total distance travelled (S) = S1 + S2

S = (150 + 150) m/s

S = 300m.

**Question 2:**

**A bus moves from rest with an initial acceleration of 2m/s^2 for the first 10 s. It then accelerates at a uniform rate of 1m/s^2 for another 15s. It continues at a constant speed for 70s and finally comes to a rest in 20s by a uniform deceleration. From the graph calculate.**

I)Total distance travelled

II) Average speed for the journey

III) Average retardation as it is brought to rest.

IV) Maximum speed attained by the motion.

Solution,

From the V-T graph

I). for the first 10s,

U= 0

a = 2m/s/s

t1 = 10s

Velocity (V)= u + at

V = 0 + (2)(10)

V = 20m/s

Distance (S1) = [(v +u)/2] t

S1 = [ (20 +0)/2] x 10

S1 = [10 x 10] = 100m

For the second 15s

U= 20m/s

t2 = 15s

Velocity (v) = ( 20 + 15) m/s

V = 35 m/s

Distance (S2) = [(v +u)/2] t

S2 = [ (35 +20)/2] x 10

S2 = [41.25 x 10] = 412.5m

For the third 70s,

V = constant at 35m/s

t3 = 70s

V = S3/t3

S3 = (35 x 70) m

S3 = 2450m

For the last 20s (Retardation or deceleration).

V = 0

U = 35m/s

t4 = 20s

S4 = [(v +u)/2] t4

S2 = [ (0 +35)/2] x 20

S2 = [35 x 10] = 350m

Total distance travelled(S)= S1 + S2 + S3 + S4

S = [ 100 + 412.5 + 2450 + 350]

S = 3312.5m

II) Average velocity = S / T

T = [ 10 + 15 + 70 + 20] s

T = 115s

V = 3312.5/115 = 28.8 m/s

Average velocity spent for the journey = 28.8m/s

III) Average Retardation = (v-u)/t4

V = 0

U = 35m/s

AR = (0 - 35)/20

AR = 1.75 m/ s (square)

Average Retardation as it's brought to rest = 1.75m/s^2

**Motion under gravity**

**Motion under the influence of gravity is based on acceleration due to gravity(g) of a free falling object and +/- g sign conventions.**

__Formula__

**Question 1**

**A cricket ball is thrown vertically upwards with an initial velocity of 40m/s . Find,**

I) it's velocity after 3s

II) Maximum height attained and the time it

III) The total time taken for the ball to return to the ground again.

Solution,

I) V = u - gt

V = 40 - 10 (3)

V = 40 -30 = 10m/s

II) using,

V = 0

U = 40m/s

g = 10m/s/s

From formula,

(40)(40) = 2 (10) h

1600 = 20 h

h =80 m

Therefore,

80 = 40t - 5t^2 ( it is now a quadratic equation)

16 = 8t - t^2

t^2 - 8t + 16 = 0

(t - 4)(t - 4) = 0

t = 4s

**Conclusion**

####
Basic equations of motion was broken down here. If you have any questions, suggestions or feedback write them below. All comments are appreciated.

Save this image below for future reference.

## Physics: All about Acceleration due to gravity (g)

### Acceleration due to gravity

Acceleration due to gravity (g) is known when a free falling object from a certain is attains a final velocity. Then take g=9.81m/s/s because this will give you a more accurate answer.The second decimal place in this numerical value are dependent primarily upon on altitude, that is why g = 9.8m/s/s sometimes. Take it as 9.8 or 10m/s/s if you are given in the question.