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Related Concept Videos

Mass and Weight01:19

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Mass and weight are often used interchangeably in everyday conversation. For example,  medical records often show our weight in kilograms, but never in the correct units of newtons. In physics, however, there is an important distinction. Weight is the pull of the Earth on an object. It depends on the distance from the center of the Earth. Weight dramatically varies if we leave the Earth's surface, unlike mass, which does not vary with location. On the Moon, for example, the...
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According to Albert Einstein (1897-1955), free-falling and feeling weightless are intrinsically linked. If a person were in free-fall under gravity, for example, diving towards the Earth from an airplane, they would feel completely weightless. Similarly, a person descending in a lift may feel partially weightless. Broadly speaking, it is assumed that an object in a uniform gravitational field and an object undergoing constant acceleration in the absence of gravity are under the same...
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Variation in Acceleration due to Gravity near the Earth's Surface01:20

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An object's apparent weight is its weight measured by a spring balance at its location. It is different from its true weight, the force with which the Earth pulls it, because of the Earth's rotation. Mathematically, an object's apparent weight equals its true weight minus the centripetal force that keeps it in a circular motion along with the Earth's surface every 24 hours.
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Weightlessness01:01

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When an object is dropped, it accelerates toward the center of the Earth. If the net external force on the object is its weight, it is said to be in free fall; that is, the only force acting on the object is gravity. Galileo was instrumental in showing that, in the absence of air resistance, all objects fall with the same acceleration g. However, when objects on the Earth fall downward, they are never truly in free fall, because there is always some upward resistance force from the air acting...
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A rocket's velocity in the presence of a gravitational field is decreased by the amount of force exerted by Earth's gravitational field, which opposes the motion of the rocket. If we consider thrust, that is, the force exerted on a rocket by the exhaust gases, then a rocket's thrust is greater in outer space than in the atmosphere or on a launch pad. In fact, gases are easier to expel in a vacuum.
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The gravitational acceleration of an object near the Earth's surface is called the acceleration due to gravity. It can be measured by conducting simple experiments on Earth. However, such an experiment is impossible to conduct on the surface of other planets.
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Body mass changes during long-duration spaceflight.

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Astronauts lost significant body mass in space due to insufficient caloric intake. Monitoring body mass using devices like the Russian BMMD and NASA

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Area of Science:

  • Space medicine
  • Human physiology in microgravity

Background:

  • Maintaining crew body mass is critical for health and research during spaceflight.
  • Accurate body mass measurement is challenging in microgravity environments.
  • Previous spaceflights show crewmembers often fail to meet caloric needs, leading to body mass loss.

Purpose of the Study:

  • To assess body mass changes in astronauts during spaceflight.
  • To compare the efficacy of two different body mass measurement devices.
  • To correlate body mass changes with in-flight dietary intake.

Main Methods:

  • Utilized two International Space Station (ISS) devices: Russian body mass measuring device (BMMD) and NASA's Space Linear Acceleration Mass Measurement Device (SLAMMD).
  • Collected data from 25 crewmembers, comparing in-flight measurements to pre-flight gravimetric data.
  • Analyzed device accuracy by comparing measurements taken within a close timeframe.

Main Results:

  • Significant body mass loss observed: -4.4% (BMMD) and -2.8% (SLAMMD) compared to pre-flight.
  • Body mass stabilized after an initial 30-day loss, regardless of the device used.
  • Average difference between BMMD and SLAMMD measurements was 1.1 kg.
  • In-flight dietary intake averaged 80% of WHO estimated requirements, closely correlating with body mass decrease.

Conclusions:

  • Body mass monitoring is essential for astronaut health and ensuring adequate energy consumption during space missions.
  • Both BMMD and SLAMMD provide valuable data for tracking body mass in microgravity.
  • Low caloric intake is a primary driver of body mass loss in spaceflight.