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7.6Physics 01. Forces And Energy

Understand that there is no air resistance to oppose movement in a… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 7 of 12 1 quiz

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Lesson summary

7.6 Movement in space: no air resistance in a vacuum — CHECKPOINT - Lower Secondary Science 0893 notes: Understand that there is no air resistance to oppose movement in a vacuum, and describe how gravity keeps planets in orbit.Air resistance — a force that acts against the moveme…

  • Speed in space
  • Large mass
  • Strength of gravity
  • Decreases with distance
  • Force towards the Sun
  • Only force

Section 1 of 8Air resistance

Air resistance
  • Air resistance a force that acts against the movement of an object through air.
  • It is caused by the moving object pushing against the particles in the air.
  • It acts in the opposite direction to the movement.
Speed
  • Speed the faster an object moves, the greater the air resistance.
Uses
  • Uses an aeroplane wing can change shape to produce extra air resistance and help slow the plane down after landing.

Section 2 of 8Vacuum

Vacuum
  • Vacuum a space where there are no particles.
  • Space is a vacuum, with very few particles.
No air resistance
  • No air resistance in a vacuum there is nothing to oppose the movement.
Speed in space
  • Speed in space objects in space do not slow down as they do on Earth.
  • The Juno probe reached a very high speed near Jupiter, which would not be possible on Earth.

Section 3 of 8Gravity of the Sun

Large mass
  • Large mass the Sun has the largest mass in the Solar System, more than all the planets together.
Strength of gravity
  • Strength of gravity the Sun's gravity is 27 times stronger than the Earth's gravity.
Decreases with distance
  • Decreases with distance the pull weakens as the distance from the Sun increases.

Section 4 of 8Orbits

Orbit
  • Orbit the almost circular path of a planet around the Sun.
Force towards the Sun
  • Force towards the Sun the force of gravity from the Sun always acts towards the Sun and turns the planet in a circle.
  • Without it the planet would move off in a straight line into space.
Only force
  • Only force the only force acting on a planet is gravity because there is no air resistance.

Section 5 of 8Speed of planets

PlanetSpeed of orbit in km/s
Mercury48
Earth30
Jupiter13
Neptune5
  • Trend
    • the further a planet is from the Sun, the slower its orbital speed.
    • Mercury is closest to the Sun, has the strongest pull and moves fastest.

Section 6 of 8Moving objects on Earth and in space

PlaceForces that slow movementResult
On EarthAir resistance and frictionMoving objects slow down
In spaceNoneObjects keep moving at constant speed

Section 7 of 8Key terms

TermMeaning
Air resistanceForce opposing the movement of an object through air.
VacuumA space with no particles.
OrbitThe path of one object around another.
Force of gravityAn attraction between objects with mass.
SpeedDistance travelled in a given time.

Section 8 of 8Exam technique

1
Planets keep moving because of a push — there is no force to slow them down in a vacuum.
2
There is air in space — space is almost a vacuum.
3
Gravity is zero in space — gravity from the Sun and planets acts throughout space.
4
Orbits are exact circles — they are almost circular.

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