Topic 7Astronomy - Session 2

Gravity and Orbits

10X2 Physics Mr Ram Week beginning 27th April 2020 (week 4)

Aims of session 2

• Recall the factors that affect the strength of the gravitational field.

• Explain why g has different values on different bodies in the Solar System.

• Describe the orbits of moons, planets, comets and artificial satellites.

• Explain why the velocity of a planet changes even if orbiting at a steady speed.

• Describe how changing the speed of an orbiting body affects the radius of its orbit.

Quick Re-cap (answer in your book)

1. What is the geocentric model of the Solar System?

2. Who suggested the geocentric model?

3. What is the heliocentric model?

4. Who is best known for suggesting the heliocentric model?

5. Name the planets in order, starting with the one nearest the Sun.

6. Put these in order of size, starting with the smallest: dwarf planet, planet, asteroid

7. Why are some telescopes put onto satellites?

8. Suggest one way in which our current model of the solar system is different to Copernicus’

Quick Re-cap: Answers1 What is the geocentric model of the Solar System?

the idea that the Sun and all the planets are moving around the Earth

2 Who suggested the geocentric model?

Ptolemy

3 What is the heliocentric model?

the idea that everything in the Solar System orbits the Sun

4 Who is best known for suggesting the heliocentric model?

Copernicus

5 Name the planets in order, starting with the one nearest the Sun.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

6 Put these in order of size, starting with the smallest: dwarf planet, planet, asteroid

asteroid, dwarf planet, planet

7 Why are some telescopes put onto satellites?

because the Earth’s atmosphere absorbs some wavelengths of EM radiation / to put them above the clouds or dust in atmosphere

8 Suggest one way in which our current model of the solar system is different to Copernicus’

more planets / Stars not fixed / Elliptical orbits

Title - Types of Orbits

The orbits of planets around the sun are not completely c____________. We describe their orbits as being e______________.

C________have h_________ e___________ orbits.

Orbits of planets

Task 1:-Copy above diagram and copy and complete gap fill below into your book.

https://www.youtube.com/watch?v=bA-V2DixZBk

Sub-title Artificial Satellites of Earth and Their Orbits

Task 2:-Watch the video clip below and copy and complete the table in your book.

Low earth orbit (LEO) Medium earth orbit (MEO)

Geostationary orbit (GSO)

Distance from Earth

Orbital speed

Main uses

Task 3:-Use the information on the diagram to answer the question below. (answer on the next slide)

Answer to Task 3

At low orbits, the force of ______ is

________, so the satellite has to move

________ to remain in orbit.

At high orbits, the force of ______ is

________, so the satellite moves at

________ speeds to remain in orbit

high speed

low speed

Task 4:-Use the information on the diagram to complete the gap fill.

Copy diagram into your bookWordlist – lower, stronger, weaker, gravity, faster.

Task 5:-Copy and answer question. This is a 3 mark question, check your answer with the model answer on the next slide.

As the satellite speeds up, the force of gravity will not be able to hold it in its current orbit (1)

This causes it to move further away from Earth (1)

As it moves further away, it will slow down, until it is in a higher orbit (1)

Check your answer

Sub-title What keeps bodies in orbit? • A planet in a circular orbit has a constant speed as it travels.

• But, its d__________ is constantly changing.

• So its v_________ will also be constantly changing since it is a v________ quantity.

• This means the body will be a____________, so therefore there must be a r____________ force acting on the body.

• This force is due to the g____________ attraction between the sun and the planet.

• The force acting on a body following a circular path is called the c__________ force.

Task 6:-Use the information on the diagram to help you complete the gap fill (copy into your book) answer on the next slide.

Sub-title What keeps bodies in orbit?

• A planet in a circular orbit has a constant speed as it travels.

• But, its direction is constantly changing. • So its velocity will also be constantly

changing since it is a vector quantity. • This means the body will be

acceleration, so therefore there must be a resultant force acting on the body.

• This force is due to the gravitationalattraction between the sun and the planet.

• The force acting on a body following a circular path is called the centripetal force.

Check your answers

Difference between mass and weight?

Task 7:- Copy this table into your book and learn the differences

Sub-title Relationship between weight and mass

weight (N) = mass (kg) x gravitational field strength (N/kg)

w = mg

The value of g depends upon:-

1. The mass of the body

2. The radius of the body

You will need to learn this equation

Task 8:- Copy all the highlighted text on this slide and make sure you understand the factors that g depends upon.

Task 9:- Answer exam-style question in your book

Task 10:- Check your answer and make any corrections.

Task 11:- Plenary – copy and complete the worksheet

Task 12 – check your answers