Gravity Affects Motion - Middle School Earth and Space Science

1. Identify the force that causes a projectile to curve downward after it is launched.

   Gravity. Gravity continuously pulls projectiles downward during flight.

2. Which quantity stays the same on the Moon: mass or weight?

   Mass. Mass is intrinsic; weight depends on local gravity.

3. What is the direction of gravitational force between two objects?

   Along the line joining them, toward each other's centers of mass. Gravity always attracts, never repels.

4. What is an orbit in terms of motion and gravity?

   Continuous free fall around a body due to gravity. Object falls toward center but horizontal velocity keeps it circling.

5. Which path best describes an object launched horizontally: straight line or parabola?

   Parabola (curved downward due to gravity). Horizontal velocity stays constant while gravity curves path downward.

6. Find the new force if $F = 12\ \text{N}$ at distance $r$, then distance becomes $3r$.

   $\frac{12}{9}\ \text{N}$. Force decreases by $r^2$: $F/3^2 = 12/9$.

7. State the relationship between orbital period and orbital radius (same central mass).

   Larger radius gives a longer orbital period. Kepler's third law: $T^2 \propto r^3$.

8. Which falls faster in a vacuum: a heavy object or a light object?

   Neither; both fall at the same rate. Without air resistance, all objects accelerate equally at $g$.

9. If $g$ decreases, what happens to an object's weight while its mass stays the same?

   Weight decreases; mass stays constant. Weight depends on $g$; mass is an intrinsic property.

10. What is inertia's role in an orbit around a planet?

    Inertia keeps forward motion while gravity bends the path into orbit. Without inertia, objects would fall straight down.

11. State the relationship between orbital speed and orbital radius (same central mass).

    Larger radius requires lower orbital speed. Need less centripetal force at larger distances.

12. Find the weight of a $2\ \text{kg}$ object on Earth using $g = 9.8\ \text{m/s}^2$.

    $19.6\ \text{N}$. Apply $W = mg$: $2 \times 9.8 = 19.6$.

13. What is the approximate gravitational acceleration near Earth's surface?

    $g \approx 9.8\ \text{m/s}^2$ downward. Standard value for calculations near Earth.

14. Ignoring air resistance, what is the acceleration of all falling objects near Earth?

    The same: $g$ downward. All objects fall at same rate regardless of mass in vacuum.

15. Which option best explains why astronauts feel weightless in orbit?

    They are in continuous free fall with the spacecraft. No contact forces in free fall creates weightless sensation.

16. At which scale does gravity dominate motion: atomic scale or planetary scale?

    Planetary scale (gravity is negligible at atomic scale). Gravity too weak to affect atoms but dominates large-scale motion.

17. What is the definition of weight in terms of gravity?

    Weight is gravitational force on an object: $W = mg$. Mass times gravitational acceleration.

18. Identify the scale where gravity mainly controls motion: atoms, people, or planets?

    Planets (and other large astronomical bodies). Gravity dominates motion at astronomical scales.

19. What is the relationship between orbital speed and orbital radius for a circular orbit?

    Larger radius means lower orbital speed. Weaker gravity at larger distances requires slower speed to maintain orbit.

20. Which option best describes tides: Moon's gravity is strongest on which part of Earth?

    On the near side (and also relatively stronger on the far side than the center). Differential pull creates bulges on both sides.

21. What is an orbit in terms of gravity and motion?

    Continuous free fall around a body due to gravity. Object falls toward center but horizontal velocity keeps it circling.

22. Identify the best description of tides: caused mainly by Earth's gravity or the Moon's gravity?

    Mainly the Moon's gravity (with the Sun also contributing). Moon's gravity pulls ocean water, creating bulges as Earth rotates.

23. What provides the centripetal force that keeps a moon or satellite in orbit?

    Gravity. Gravitational attraction provides inward force for circular motion.

24. What is the definition of an orbit in terms of gravity and motion?

    Continuous free fall around a body due to gravity. Object falls toward center but misses due to sideways motion.

25. Which object exerts the greater gravitational force: Earth on you or you on Earth?

    They are equal in magnitude. Newton's third law: forces always come in equal and opposite pairs.

26. What is the approximate value of Earth's gravitational field strength at the surface?

    About $9.8\ \text{N/kg}$ (about $9.8\ \text{m/s}^2$). This value means 1 kg experiences 9.8 N of gravitational force.

27. Which option describes free fall correctly (ignore air resistance)?

    Objects accelerate downward at $g$ regardless of mass. Galileo showed all objects fall at same rate without air.

28. Identify the main force that provides the centripetal force for planets in orbit.

    Gravity. Gravitational attraction provides the inward pull for circular motion.

29. What is the direction of the gravitational force on an object near a spherical planet?

    Toward the planet's center of mass. Gravity always pulls objects toward the center of spherical bodies.

30. What happens to gravitational force when one mass doubles (distance unchanged)?

    It doubles. Force is directly proportional to each mass.

31. Which scale best matches gravity as the dominant force: atomic scale or planetary scale?

    Planetary scale. Gravity dominates motion of planets, moons, and stars.

32. Identify the direction of gravitational force near Earth: upward, downward, or sideways.

    Downward, toward Earth's center. Gravity always pulls toward the center of mass.

33. What happens to gravitational force when distance doubles (masses unchanged)?

    It becomes $\frac{1}{4}$ as strong. Force follows inverse square law: $2^2 = 4$ times weaker.

34. Identify the correct cause of falling objects accelerating: gravity or an initial push?

    Gravity causes the acceleration. Gravity provides the downward force for acceleration.

35. What is the definition of gravity in Earth and space science?

    An attractive force between objects with mass. Gravity pulls all matter together, stronger for more massive objects.

36. What is the main reason astronauts feel weightless while orbiting Earth?

    They are in continuous free fall with their spacecraft. Both astronaut and spacecraft fall together, creating apparent weightlessness.

37. What happens to orbital speed when a satellite orbits closer to Earth (lower orbit)?

    Orbital speed increases. Closer orbits require higher speeds to balance stronger gravity.

38. What is the difference between mass and weight?

    Mass is matter; weight is gravitational force on mass. Mass is constant everywhere; weight varies with gravitational field strength.

39. What is free fall?

    Motion when gravity is the only significant force. No other forces act, so objects accelerate purely due to gravity.

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