Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

1.3Unit 3: The Solar System and energy

Movement in space

5 min read 7 parts Lesson 3 of 7 1 quiz

0%read
Lesson summary

1.3 Movement in space — CHECKPOINT EARTH AND SPACE 0893 notes: Explain how the Sun's gravity keeps the planets in orbit, why orbit speeds differ and why objects keep moving in space.Mass — the Sun has the largest mass in the Solar System, more than all the other planets added tog…

  • Holding planets
  • Orbit shape
  • Turning force
  • Without gravity
  • Other objects
  • Closest planet

Section 1 of 7The Sun and its gravity

  • Mass
    • the Sun has the largest mass in the Solar System, more than all the other planets added together
  • Strength
    • gravity on the Sun is 27 times stronger than on Earth
  • Holding planets
    • the Sun's gravity holds all the planets in their orbits
  • Distance
    • the Sun's gravity gets weaker as the distance from the Sun increases
  • Neptune
    • although it is 30 times further away than Earth, the Sun's gravity is still strong enough to hold it in orbit

Section 2 of 7Keeping a planet in orbit

  • Orbit shape
    • the orbits of the planets are almost circular
  • Turning force
    • any object moving in a circle needs a force that makes it turn
  • Direction
    • the Sun's gravity on a planet always acts towards the Sun
  • Without gravity
    • the planet would travel off in a straight line into space
  • Other objects
    • comets and asteroids are kept in orbit around the Sun by the same force

Section 3 of 7Speeds of the planets

  • Closest planet
    • Mercury feels the strongest pull from the Sun and moves fastest
  • Speed values
    • Mercury averages 170 000 km/h and Earth averages about 100 000 km/h
  • Trend
    • the further a planet is from the Sun, the slower it orbits
  • Orbit speeds (km/s)
    • Mercury 48, Venus 35, Earth 30, Mars 24, Jupiter 13, Saturn 10, Uranus 7, Neptune 5
  • Not exact circles
    • a planet moves slightly faster when it is nearer the Sun and slightly slower when further away

Section 4 of 7Air resistance on Earth

  • Air resistance = a force caused by a moving object pushing against the particles in the air
  • Direction
    • it acts in the opposite direction to the movement
  • Speed
    • the faster an object moves, the greater the air resistance
  • Use
    • an aeroplane wing can change shape to add air resistance and slow down faster after landing

Section 5 of 7Movement in a vacuum

  • Vacuum = a space with no particles in it
  • Space
    • there are very few particles in space, so there is almost no air resistance
  • Spacecraft
    • the Juno probe reached a very high speed near Jupiter that would be impossible on Earth because of air resistance
  • Planets
    • Earth and the other planets move in a vacuum, so nothing slows them down
  • Forces on a planet
    • the only force acting on a planet is gravity

Section 6 of 7Discovering Neptune

  • Observation
    • the measured orbit of Uranus differed from the calculated orbit
  • Explanation
    • scientists proposed that another source of gravity was pulling Uranus
  • Prediction
    • they used the orbit of Uranus to predict where an unknown planet should be
  • Result
    • Neptune was found in 1846 very close to the predicted place
  • Meaning
    • the discovery supported the prediction

Section 7 of 7More from the specification

  • Orbital speed and distance
    • Planets closer to the Sun experience stronger gravitational force and must orbit at higher speeds to maintain stable orbits.
  • Vacuum of space
    • Outer space is an almost complete vacuum with no air resistance or atmospheric friction to slow down moving spacecraft.
  • Interpreting planetary data graphs
    • Graphing planetary distance against orbital speed reveals a non-linear relationship where orbital velocity decreases outwards.
  • Secondary data analysis
    • Drawing evidence-based predictions and conclusions using published astronomical data tables and spacecraft telemetry.

Last updated: