Fill in the Blanks Lesson 1.3a Fill-in-Blanks: Forces Within A StarOnline version Test your knowledge on the forces that act within a star! by Eric D Norman 1 star energy forces mass nuclear fusion gravity helium hydrogen core equilibrium inward Forces Within a Star There are several acting on a . Every object in the universe that has ( e . g . , atoms , planets , the Sun , yourself ) , generates , a force that attracts other objects and particles towards its center . This force is very weak , but the more mass an object has , the more gravity it generates . Inside a star , gravity pulls , trying to collapse the star in on itself . You can picture this by imagining your hands squeezing a stress - ball . When gravity pulls gas particles together inside a star , they collide more frequently and with more force , which leads to . A small percentage of the mass from the hydrogen gas is lost when it is fused into , because it is converted into tremendous amounts of . This net gain in energy from nuclear fusion in the pushes outward , trying to blast matter into space . Stars whose size changes relatively little have achieved a state of , which means that the forces pushing in and the forces pushing out are equal and balance each other out . As long as the star has enough hydrogen fuel in its core to continue fusion reactions , the star will maintain equilibrium and stay as a main sequence star . This means that when the star shrinks or expands , it is because the force of gravity that pushes inward and the internal fusion force that pushes outward are not equal anymore . In other words , the forces are not in equilibrium .
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