How fast do the Planets move?

INVESTIGATION

What is the order of the planets, from closest to the sun to furthest away?

How fast are you travelling right now?

What information would a scientist need to investigate the speed of an object?1. Speed = Distance

Time2. Need to know: The orbital distance of eachPlanet and the time it takes for the planet tomove around the sun.

3. What units should we use to represent speed?

What´s appropriate?

An Astronomical Unit (AU)

One Astronomical Unit is the approximate

distance between the Earth and the Sun.

1 AU ≈ 149,600,000 km.

Why is 1 AU an approximate distance and not exact?

1.The Earth´s orbit is an ellipse not a perfect circle.

2.There are slight variations in the Earth´s Orbit.

Problem that we now face:

How do you find the circumference of an ellipse?

Formulae do exist but it requires advanced mathematical techniques to derive.

Are there any shapes that are slightly more simple than an ellipse that we do know how to find the circumference of?

Assumptions in Mathematics

Often Mathematicians cannot always find

exact answers to problems because it would

make the problem too difficult to solve.

In these cases, we make simpler assumptions.

We can assume that the orbit is circular to decrease the complexity of the problem and find an approximate answer.

Planet Mercury

Venus

Earth Mars

Jupiter

Saturn

Uranus

Neptune

Orbital Radius (AU)

0.38 0.72 1 1.52

5.2 9.45 19.2 30.06

Time to orbit Sun

88 days

225 day

s

365 .25

days

687 day

s

11.9 years

29.45

years

84 years

164.8 years

Data

Pair Challenge 1: a) The approximate speed of Mercury is 172800 km/h. Use the data to confirm this.b) Change your answer to part a) into km/s and then m/s. Write these answers to 3 significant figures.

Planet Mercury

Venus

Earth Mars

Jupiter

Saturn

Uranus

Neptune

Orbital Radius (AU)

0.38 0.72 1 1.52

5.2 9.45 19.2 30.06

Time to orbit Sun

88 days

225 day

s

365 .25

days

687 day

s

11.9 years

29.45

years

84 years

164.8 years

Data (1 AU = 149600000 km)

Pair Challenge 2: a) Use Excel to find the speeds of all the

planets in the solar system in km/h, km/s and in m/s.

b) Look at the answers you have in km/s. Do you notice anything? How could would represent this information in a more visual way?

Topics DiscussedContent1.12, 1.13 - Speed, Distance and Time6.3 - Circumference of Circles6.1 - Converting between measurements.11.3 - Scatter Graphs and Correlation.1.10 - Significant Figures1.9 – lead onto Standard form.SkillsSimplifying a problem by making

assumptions.Ways of displaying data.Appropriate Answers