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Inertia, Mass, Weight

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Inertia

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Inertia

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What is Inertia? a property of matter.
a measure of an object’s resistance to changes in its motion. resistance to changes in speed and/or direction. directly proportional to an object’s mass. more massive objects have more inertia.

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Mass and Weight How are they different?

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Mass is … the amount of matter in an object.
a measure of the inertia of an object. measured in units of kilograms. constant everywhere. No matter where I take you, your mass doesn’t change. Figure 58: Sample Scale (63k) This lightweight (230 gram) but durable scale was flown on Apollo 14 thru 17. The readings are given in terrestrial pounds.

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Weight is … another name for the force of gravity which the planet exerts on an object near its surface. We typically speak of our weight on Earth so we are talking about the force of gravity that the Earth exerts on us. a force. dependant on BOTH your mass and the planet which you are on or near. Figure 58: Sample Scale (63k) This lightweight (230 gram) but durable scale was flown on Apollo 14 thru 17. The readings are given in terrestrial pounds.

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How do you “weigh” an astronaut?
Out in Space How do you “weigh” an astronaut?

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How to “Weigh” an Astronaut
An astronaut onboard the space shuttle measures his “weight” (actually his mass) with a Body Mass Measurement Device. Right: From Biomedical Results from SkyLab, Ch. 19, sect. 3, “Physiological Mass Measurements in SkyLab,” 27 October 2008.

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Weight Calculations Weight = Mass * (Gravitational Field Strength)
Gravitational Field Strength depends on the planet and the exact location. On Earth, gravitational field strength = g= 9.8N/kg. In other words, the earth exerts 9.8N of force on you for every 1 kg of mass. On Earth, Weight (in Newtons) = Mass (in kilograms) * 9.8N/kg

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English versus Metric Units
English Units Mass Kilograms Slugs Weight Newtons Pounds (lbs) Note: 9.8 Newtons = 2.2 lbs

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Question #1 Determine the weight (in Newtons) of a 64 kg object on planet Earth.

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Question #2 Determine the mass (in kilograms) of an object which weighs 200 N on planet earth.

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