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Physics

Physics. PHS 5043 Forces & Energy Gravitational attraction. Force: Any agent capable of changing the shape of an object or changing its state of rest or motion Symbol: F Units: N (newton). PHS 5043 Forces & Energy Gravitational attraction. There two main types of forces:

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Physics

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  1. Physics

  2. PHS 5043 Forces & EnergyGravitational attraction Force: Any agent capable of changing the shape of an object or changing its state of rest or motion Symbol: F Units: N (newton)

  3. PHS 5043 Forces & EnergyGravitational attraction There two main types of forces: _Forces acting at a distance _Forces acting upon contact

  4. PHS 5043 Forces & EnergyGravitational attraction Main forces acting at a distance: _Gravitational force _Electromagnetic force _Weak nuclear force _Strong nuclear force

  5. PHS 5043 Forces & EnergyGravitational attraction Law of universal gravitation: “Every object in the universe attracts every other object with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres”

  6. PHS 5043 Forces & EnergyGravitational attraction Gravitational attraction Fg : (Gravitational force) Fg = G m1 m2 / d2 _Fg is gravitational attraction force (unit : N) _m1& m2are the masses of the two objects (unit: kg) _ d is the distance between the centers of each object (unit: m) _ G is the universal gravitational constant (value: 6.67 * 10 -11 unit: Nm2/kg2)

  7. PHS 5043 Forces & EnergyGravitational attraction Example: Calculate the gravitational force between two people with masses of 60 and 70 kg respectively, separated by a distance of 2 meters. Fg = G m1 m2 / d2 Fg = (6.67 * 10 -11Nm2/kg2) (60kg) (70kg) / (2m)2 Fg = 7 * 10 -8 N

  8. PHS 5043 Forces & EnergyMass & Weight Mass of an object: Amount of matter an object contains Symbol: m Units: kg *The mass of an object does not change

  9. PHS 5043 Forces & EnergyMass & Weight Weight of an object: (universal gravitation) Defined by the product of the mass of the object and the strength of the gravitational field (g) in which it is located Symbol: Fg Formula Fg= m g Units: N *The weight of an object changes with its location

  10. PHS 5043 Forces & EnergyMass & Weight Obtaining “g”: Measuring the weight of an object, is measuring the gravitational attraction that Earths exerts on it. Thus: Fg = G m1 m2 / d2 Fg = m2 (G m1/ d2 ) m1: mass of Earth (5.98*1024 kg) d: radius of Earth (6.38 * 106 m) G:universal gravitational constant (6.67 * 10-11Nm2/kg2) Fg = m2 (6.67 * 10-11Nm2/kg2) (5.98*1024 kg) / (6.38 * 106 m)2 Fg = m2 (9.8 N/kg) Fg = m2 g

  11. PHS 5043 Forces & EnergyMass & Weight The weight of an object changes with its location: Fg= mg _Higher latitudes, higher “g” since Earth radius is smaller, therefore objects are heavier _Higher altitudes, lower “g” since longer distance between object and Earth center, therefore objects are lighter _Planets with more mass than Earth will have higher “g”, therefore objects are heavier _Planets smaller than Earth will have higher “g” since their radii would be smaller, therefore objects are heavier

  12. PHS 5043 Forces & EnergyMass & Weight Weightlessness: State by which objects appear to have no weight, due to continuous falling (free fall). Example: astronauts in space stations Regardless of appearances objects in state of weightlessness are acted on by gravitational forces (by Earth or other planets)

  13. PHS 5043 Forces & EnergyMass & Weight Weightlessness: PROS: Can produce interesting results for scientific research (e.g. crystallization and synthesis) due to the lack of gravity CONS: Affects blood circulation, and the structure of bones and muscles

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