<h2>Answer: Gravitational attraction
</h2>
Gravity force causes the clouds of dust and gas to form a protostar. As this <u>attraction force</u> is responsible for gathering and compressing the existing elements in the cloud of gas and dust, heating them during this process.
Then, when the amount of material accumulated by gravitational contraction is large enough, and the temperature and pressure reached high enough, the <u>nuclear fusion</u> process will begin.
To understand it better: The hydrogen nuclei will begin to fuse, generating helium nuclei in the process and releasing huge amounts of energy.
It should be noted that the protostars radiate half of the energy contributed by the gravitational collapse and the other half is invested in heating its core.
A type O star is likely to appear blue.
66° N and 90° N
the area of the artic circle in the northern hemisphere
<h3>
Answer:</h3>
Input work
<h3>
Explanation:</h3>
Concept being tested: Efficiency of machines
Therefore we need to know what is the efficiency of a machine
- Efficiency of a machine is the ratio of work output of machine to the work input expressed as a percentage.
Efficiency = (Work output ÷ Work input) × 100%
- Therefore, if the work input is equal to the work output then the efficiency of the machine will be 100%.
- Most machines are not 100% efficient due to loss of energy in form of heat due to friction of the moving parts of the machine.
