The theory that explains gravity is a. special relativity b. general relativity c. quantum mechanics
Gravity is a. the strongest force b. the second strongest force c. the weakest force
The electromagnetic force a. changes particle types b. holds particles together in the nucleus of an atom c. controls the attraction and repulsion of charged particles
Discussion/essay questions
Unifying the forces is one part of a big problem for scientists. Scientists use two theories to explain the universe: relativity and quantum theory. These theories have different laws. Scientists hope to find a “theory of everything” that uses the same laws to explain all things. Do you think it is possible for humans to discover the theory of everything? Why or why not?
Transcript
The fundamental forces are the four basic forces that control interactions of matter. The most well-known force is gravity. This is the force that draws large objects together. The theory that explains gravity is Einstein’s theory of general relativity. General relativity states that massive objects bend space and time, which causes other objects to fall toward them. However, gravity is the weakest force. The other forces are the electromagnetic force, the weak nuclear force, and the strong nuclear force. These forces work on small particles. The electromagnetic force controls the attraction and repulsion of charged particles, like protons and electrons. The weak nuclear force can change one particle into another type of particle. The strong nuclear force holds particles together in the nucleus of an atom. Scientists believe that at the beginning of time, all four forces were unified. This is difficult to prove, because the laws of general relativity don’t work at small scales. This means that there is no current theory that can unify gravity with the other forces.
The escape velocity is a. the maximum mass of an object travelling into space b. the minimum mass of an object to be a strong source of gravity c. the minimum constant speed of an object travelling into space
The escape velocity of Earth is about a. 9.8 km/s b. 11.2 km/s c. 40,000 km/s
It would be easiest to launch an object from a. Earth b. the Moon c. a black hole
Discussion/essay questions
Reaching outer space was an important achievement in human history. What kinds of space exploration do you think will be possible in the future?
Transcript
Every source of gravity in the universe has an escape velocity. This is the minimum constant speed that an object has to travel to fully escape from a planet or star and enter outer space. For an object of any mass to be launched into space from Earth, it must be travelling at about 11.2 km/s, or 40,000 km/h. To determine escape velocity, scientists need to know the mass and radius of the source of gravity. Escape velocity increases for planets and stars with more mass. It would be easier to launch something from the Moon than from Earth. For a black hole, which has infinite density, the escape velocity is greater than the speed of light. This is why nothing can possibly escape from its gravity.
Dark energy is a force that exists throughout the universe. It is believed to make up about 68% of everything that exists, and it affects the way the universe is expanding. have known about the expansion of the universe since 1929. But for many years, most believed that the force of gravity would eventually slow down this expansion. However, in the 1990s, a team of astronomers that the universe was actually expanding than it had been years before. They came to the conclusion that there was another force, called dark energy, that was causing the expansion to accelerate. Dark energy is even than gravity, and scientists still don’t know much about it. It has often been called the universe’s greatest mystery.
Comprehension questions
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Discussion/essay questions
There is a lot to learn about the universe. If you could ask an astronomer any question, what would you ask?
Transcript
Dark energy is a mysterious force that exists throughout the universe. It is believed to make up about 68% of everything that exists, and it affects the way the universe is expanding. Scientists have known about the expansion of the universe since 1929. But for many years, most believed that the force of gravity would eventually slow down this expansion. However, in the 1990s, a team of astronomers observed that the universe was actually expanding faster than it had been years before. They came to the conclusion that there was another force, called dark energy, that was causing the expansion to accelerate. Dark energy is even stronger than gravity, and scientists still don’t know much about it. It has often been called the universe’s greatest mystery.
One of Newton’s most famous quotes is “if I have seen further it is by standing on the shoulders of giants”. What do you think he meant by this?
Transcript
Isaac Newton was an English physicist and mathematician. He was born in 1643 in Woolsthorpe, England. In 1661, he moved to Cambridge to study at Trinity College. During his studies, Newton went into quarantine because of an outbreak of the plague. He made some of his most important scientific discoveries while working from home. Newton is best known for developing the theory of gravity and writing the three laws of motion. However, he made many other contributions to math and science, including the invention of calculus. He also published multiple books about his discoveries. Newton died in 1727, at the age of 84. He is still considered one of the greatest scientists of all time.
