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Weight and mass

Weight and mass. T.H. What units are used by this weighing scale?. The scale on the left uses newtons. The scale on the right uses kilograms (in red) and stones (in black). Compare the readings. Newtons are much smaller than kilograms. How many newtons are there in a kilogram?.

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Weight and mass

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  1. Weight and mass T.H. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan

  2. What units are used by this weighing scale? PDST Resources for Leaving Certificate Physics2

  3. The scale on the left uses newtons. The scale on the right uses kilograms (in red) and stones (in black). Compare the readings. PDST Resources for Leaving Certificate Physics3

  4. Newtons are much smaller than kilograms. How many newtons are there in a kilogram? PDST Resources for Leaving Certificate Physics4

  5. It depends what planet you’re on! On the moon, 1 kg has a weight of only 1.6 N On earth, 1 kg has a weight of 9.8 N PDST Resources for Leaving Certificate Physics5

  6. On Earth Sean reads 69 kg or 676 N. PDST Resources for Leaving Certificate Physics6

  7. On the moon, Sean would still have a mass of 69 kg, but his weight would be only 110 N.So, one way to lose weight is to go to the moon. PDST Resources for Leaving Certificate Physics7

  8. Is mass the same as weight? • What’s your opinion? • Can you think of any differences between the two quantities? PDST Resources for Leaving Certificate Physics8

  9. Mass and weight • The weight of an object is due to the force of gravity acting on it. It is measured in newtons. A body’s weight can change depending on whether it’s on earth, the moon, mars and so on. • Mass is measured in kilograms. According to one definition, it is a measure of the resistance of a body to motion. Unlike your weight, your mass won’t change if you move to another planet. PDST Resources for Leaving Certificate Physics9

  10. W = mg • Weight = mass multiplied by the acceleration due to gravity • Jane has a mass of 58 kg. Find her weight on each of the following: PDST Resources for Leaving Certificate Physics10

  11. Answers PDST Resources for Leaving Certificate Physics11

  12. A Final Question • Is g = 9.8 m s–2 everywhere on earth? PDST Resources for Leaving Certificate Physics12

  13. Answer • No. Comparing cities, it is lowest in Mexico City (9.779 m s–2) and highest in Oslo (Norway) and Helsinki (Finland) (9.819 m s–2). • Standard gravity, or standard acceleration due to free fall, usually denoted by g0 or gn, is the nominal acceleration of body in a vacuum near the surface of the earth. It is defined to be precisely 9.80665 m s–2. PDST Resources for Leaving Certificate Physics13

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