An astronaut inside a spacecraft orbiting the earth feels weightless because
- A.There is no gravity at that height
- B.The spacecraft and the astronaut are both in free fall around the earth
- C.The mass of the astronaut becomes zero
- D.The spacecraft is beyond the atmosphere
Correct answer
Explanation
The correct answer is B, the spacecraft and the astronaut are both in free fall around the earth. In orbit the gravitational pull of the earth is the very force that keeps the craft curving around the planet, and the craft, the astronaut and everything inside accelerate towards the earth at the same rate. Since the floor no longer pushes up on the astronaut, nothing presses on anything else and the sensation of weight disappears, although true weight is not zero.
Option A is a common misconception: gravity at the height of a low orbit is only slightly less than at the surface, certainly not absent. Option C is wrong because mass is the quantity of matter in a body and does not change with position; it is the apparent weight that vanishes. Option D is wrong because leaving the atmosphere has no bearing on gravitational force, which acts through empty space. The phrase to remember is that weightlessness is a state of free fall, not a state without gravity.
Read the full article: Gravitation and Pressure: Laws, Formulas and Facts
Practice Questions
View allWhat is the SI unit of pressure?
- A.Newton
- B.Pascal
- C.Joule
- D.Watt
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Pressure is thrust per unit area, so its unit is one newton per square metre, and this unit is named the pascal after Blaise Pascal.
Read the full explanation →The value of acceleration due to gravity on the earth is maximum at which of the following?
- A.The equator
- B.The poles
- C.The centre of the earth
- D.The top of Mount Everest
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The earth is flattened at the poles, so the distance from the centre is least there, and since g varies inversely as the square of that distance, g is largest at the poles.
Read the full explanation →The escape velocity from the surface of the earth is approximately
- A.7.9 kilometres per second
- B.9.8 kilometres per second
- C.11.2 kilometres per second
- D.24 kilometres per second
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Escape velocity is the minimum speed a body must be given so that it leaves the gravitational pull of the planet and never returns.
Read the full explanation →Hydraulic brakes used in automobiles work on which principle?
- A.Archimedes' principle
- B.Pascal's law
- C.Bernoulli's principle
- D.Newton's law of gravitation
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Pascal's law states that pressure applied to an enclosed fluid is transmitted undiminished in every direction to all parts of the fluid and to the walls of the container.
Read the full explanation →The upward force experienced by a body immersed in a fluid is equal to the weight of the fluid displaced by it. This statement is known as
- A.Pascal's law
- B.Archimedes' principle
- C.Hooke's law
- D.Boyle's law
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It states that a body immersed wholly or partly in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced, so the apparent loss in weight of the body equals the weight of the displaced fluid.
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