Grade 10 Science – Unit 3 Lesson 9
Energy generated by the explosion
The atomic bomb dropped on Hiroshima, called Little Boy, generated a huge
amount of energy when it exploded. The amount of energy generated by the
bomb was equivalent to the amount of energy generated by a 15-kiloton TNT
The energy created by the atomic bomb was “consumed” in three ways:
Half of the energy was consumed when the explosion generated an ultra high
air pressure which resulted in very strong bomb blast (wind).
One-third of the energy was consumed when the explosion generated heat,
One-sixth of the energy was consumed when the explosion generated
Draw a Pie-Chart to illustrate the energy consumption.
On the ground, beneath the explosion centre (hypocentre), the temperature rose
to approximately 3,800 OC.
On the stairway of the entrance to a bank, which was 0.4 km from the explosion
centre, a man was sitting waiting for its opening. The surface of the stone
stairway was changed by the immense heat. The part where the man was sitting
remained unchanged because his body absorbed the heat.
Roof (ceramic) tiles on houses within two kilometre radius from the explosion
centre melted, and gray stones which contained silicon particles became white.
In that same area, the clothes which people wore were burnt by the heat.
An ultra high pressure was generated by the explosion. The wind velocity on the
ground beneath the explosion center was 1,580 km/hr, which is five times
stronger than the wind generated by strong hurricanes. The pressure was 3.5 kg
per square centi-metre (8,600 lb/ft2).
At a point 0.5 km from the explosion centre, the wind velocity was 1,000 km/hr.
Most of concrete buildings inside this range were completely destroyed.
Even two kilometres from the explosion centre where the wind velocity was 300
km/hr, all brick buildings were completely destroyed.
The explosion generated Alpha, Beta, Gamma and neutron rays. Alpha and Beta
rays were absorbed by the air and did not reach to the ground. Gamma and
neutron rays were strong enough to reach the ground; thus it was these rays that
Within 0.2 km radius from the explosion centre, most people died within a few
hours (even in the case where they were not directly exposed to the heat or
wind). Within a 0.8 km, most people died within 30 days after the explosion.
The people who entered the area within a half mile radius from the explosion
center in the first 100 hours after the explosion were also affected by the
remaining radiation on the ground.
Fortunately it has not been observed that the long term effects of radiation
affected A-bomb survivors nor that a radiation exposure caused genetic
Create a graph to represent the strength of the Bomb Blast from the centre of the
Research the Manhattan Project. What was it? How did it work? Describe it.
Grade 10 History – Unit 3 – Lesson 9
On 6 August 1945 at 08:15 (Japanese Standard Time), the nuclear bomb
Little Boy was dropped on Hiroshima.
The bomb was dropped by the USA B-52 bomber Enola Gay.
The strong wind generated by the bomb destroyed most of the houses
and buildings within a 1.5 miles radius. When the wind reached the
mountains, it was reflected and again hit the city. The wind caused the
most serious damage to the city. About 68% of the city’s buildings were
The blast killed directly an estimated 80,000 people. In the following
months, more people died from injuries or radiation poisoning. More than
140,000 people died within one year. In the end, the total number of
people who have died was over 200,000.
On 9 August 1945, a second atomic bomb, Fat Man, was dropped on
Nagasaki. This bomb was bigger, but due to geographic position of
Nagasaki on open plains, the damage was less and fewer people were
killed. At this site, 70,000 people died within one year.
Twenty-three American POWs were killed in the Hiroshima blast.
Was the Nuclear Bombing of Japan necessary?
The war in Europe ended May 1945, but Japan still fought frantically. Its
military was still very strong.
USA demanded the unconditional surrender of Japan. The Japanese
rejected the demand. They feared for their Emperor (…who was
considered a God…) in an unconditional surrender. The USA could have
offered to retain the Emperor as a peace condition.
USA desired revenge for Pearl Harbour. Within the USA military, there
was desire to test a new weapon and demonstrate military might to the
In 1938, the League of Nations established an international law
(Protection of Civilian Populations against Bombing from the Air in case of
War). Bombing of civilians was illegal. Recall, the USA, Germany and
Japan were not members of the League of Nations. USA President
Roosevelt noted that (1) bombing of civilians was barbaric and (2) Allied
forces should not undertake civilian bombings…if the same rules of
warfare are observed by the enemy.
In July 1945, Japan sought Russia’s help to end the war, but Russia
declared war on Japan. With Russia as its ally, the USA could have
threatened to invade Japan on two fronts.
The Japanese were never threatened with the atomic bomb (i.e.,
surrender or we will use it). The bomb was just dropped.
An American sea blockade had effectively stopped the flow of war
materials to Japan, and the USA bombings were destroying the Japanese
USA leaders wanted to minimize the loss of American lives in a prolonged
ground war. It was estimated another 500,000 American soldiers would
be killed in a prolonged fight with Japan. The estimate has since been
challenged and losses were set at 40,000 killed.
The USA dropped its second bomb only three days after the first bombing.
They did not wait very long to see if the first bombing would build
momentum for peace.
Within Japan, people seeking peace were often killed by the Japanese
military. Still, the “doves” would have fought if their Emperor was
Many American scientists working on the bomb petitioned the USA
Government not to use the weapon unless the Japanese Government was
fully advised of the bomb. The Director of the Project would not allow the
petition to be forwarded. (NOTE: His position on using the bomb
changed after WWII)
On 14 August 1945, the Japanese Emperor ordered his people…and thus,
the Government of Japan…to surrender.
Was it necessary? What were the outcomes in the world?
In 1955, 25 Japanese women disfigured by the blast and radiation went to
the USA for reconstructive surgery. The 25 women, called the Hiroshima
Maidens, underwent 138 surgeries. Their journey was sponsored by a