Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

PHYSICS · Stage 7 · Chapter 5: The Earth in Space

Physics Stage 7 Comprehensive Review

5 min read 5 parts Lesson 11 of 11

0%read
Lesson summary

Physics Stage 7 Comprehensive Review — Alhussan International Academy — Physics (Stages 7–9) notes: Summarise Stage 7 ideas on gravity, falling objects, static charge, exoplanets and models of the Universe.Gravity between all masses — There is a force of gravity between any two o…

  • Air resistance
  • Large and small leaf
  • Charging by rubbing
  • Balloon and wall
  • 51 Pegasi b
  • Geocentric model

Section 1 of 5Gravity

1Gravity between all masses3 points
  • There is a force of gravity between any two objects with mass, including a person and a chair.
  • The force is only noticeable when at least one object has a very large mass, such as a planet.
  • Between a person and a chair the force is tiny because the masses are small.
2Weight2 points
  • Weight = mass × gravitational field strength (W = m × g).
  • On Earth g is about 10 N/kg.

Section 2 of 5Falling objects and air resistance

  • Air resistance
    • This is a friction force on an object moving through air.
  • Large and small leaf
    • A small leaf dropped with a large leaf hits the ground first.
    • The large leaf has a bigger surface area, so it experiences more air resistance.
    • In a vacuum both would fall together.

Section 3 of 5Static electricity

  • Charging by rubbing
    • Rubbing transfers electrons, and the total charge stays the same.
  • Balloon and wall
    • A positively charged balloon attracts electrons in the surface of the wall, so the wall surface becomes negatively charged.
    • Unlike charges attract, so the balloon is pulled towards the wall.

Section 4 of 5Exoplanets and surface temperature

  • Exoplanet = a planet orbiting a star other than the Sun.
  • 51 Pegasi b
    • The first exoplanet found around a Sun-like star.
    • It orbits extremely close to its star, completing an orbit in about four days.
    • It receives far more energy than the Earth, so its surface temperature is much higher.

Section 5 of 5Models of the Universe

  • Geocentric model
    • The Earth is at the centre and the Sun, Moon, planets and stars orbit it.
  • Heliocentric model
    • The Sun is at the centre of the Solar System and the Earth is a planet that orbits it.
  • Backward motion of planets
    • The heliocentric model explains this more simply.
Stage in developing the modelExample
QuestionWhy do planets sometimes seem to move backwards?
EvidenceObservations of planets and Galileo's telescope views of Jupiter's moons
ExplanationPlanets orbit the Sun (heliocentric model)

Last updated: