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Pages

1Where is Mars?2How long will it take to get to Mars?3Getting to Mars4How do rockets get off the ground?5Producing Thrust6What happens when rocket fuel burns?7Your mission to Mars!8Our need for oxygen9How oxygen gets to our cells10The effects of gravity11How low gravity affects bones12Preventing bones and muscles from becoming weak13Living and working in space14What do astronomers know about Mars?15A space-craft view of Mars16Exploring Mars17Energy for exploration18The rocky surface of Mars19More about the surface of Mars20The Martian atmosphere21The importance of water22The water cycle on Earth23Is there water on Mars?24Surviving on Mars25Your Martian home26Farming on Mars27Soil on Mars28Plants for Mars29Getting energy on Mars30Where will you go next?

Practicals

1Modelling the solar system in the school yard2Rocket Practical3Investigate the Energy in Fuels4Making a Telescope5What factors affect the output of a solar cell?6Modelling Diffusion7Examining Slides of Blood8What bones are like without calcium salts9Flame Test to Identify Metals10The Different States of Water11Water Purification for Human Consumption12Factors Affecting Germination13Solar Cells for Devices14Mars Bingo
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Bone Salts

When in space, in most parts of your spacecraft, you would float from place to place (though your spacecraft would be quite small, so you would not float very far!). Therefore, you wouldn’t need to stand upright, and you wouldn’t need your bones so much for support. In this situation, your bones become thinner and weaker.

What materials in our bones make them strong?
bone salts, mainly calcium carbonate and calcium phosphate (ie. calcium salts)

What bones are like without calcium salts

View Practical >

Without gravity, bones start to lose their salts (demineralization). The size of the bone may remain the same, but the bone salts are more spread out inside the bone: this means that the bones become less dense (or, put another way, the density of bone decreases).

Density

What is density?
The mass of material in a given volume

Imagine that you had in front of you three plastic cubes of identical size, but each is filled with a different material: lead, cork and air.

Which cube would be heaviest?
The cube containing lead. Even though the cube is exactly the same size as the other two, and holds the same volume, lead is denser than cork or air (there are more atoms of lead present), so this would be the heaviest.
Which cube would have the lowest density, and how do you know?
The cube containing air, because it would be the lightest (ie. with the lowest mass).

When bones lose bone salts, the appearance of the bone changes, and you can see this in the image below. It shows pieces (sections) of bone from different people, each of whom have different levels of bone salts. Use the picture to answer the questions which follow:

Llun Gwyddoniaeth / Science Image
1
Which of the bone sections above shows the highest loss of bone salts? How do you know?
The picture on the far right, because the holes inside the bone are big (there are holes in the bones to the left, also, but these are much smaller - this is normal).
2
Which of the bone sections shows the highest bone density?
The picture on the far left, because there is more material (bone salts) within an equivalent volume of bone
3
Osteoporosis is a condition which affects bone density. Explain what happens to bones affected by this condition, and also find out who is likely to suffer from this condition.
When people suffer from osteoporosis, bone salts are lost from their bones quite rapidly, so their bone density decreases, and their bones become weak. This condition often affects elderly women, and may lead to more bone fractures or breakages.

We can calculate the density of any material using the formula below:

density = mass ÷ volume

Imagine that you are a pathologist in a hospital (examining dead bodies!). You have been given a sample of bone, and you need to find its density. The volume of the bone is 10 cm3, and its mass is 15g. The worked example below shows you how to calculate the value of density:

volume is 10 cm3; mass is 15g. 
density = mass ÷ volume
density = 15 ÷ 10
density = 1.5 g/cm3
You are given a small sample of bone from an astronaut from the International Space Station, and you need to find out if the bone density has become dangerously low. The volume is 5cm3, and the mass is 5g. What is the value of density?
1g/cm3
(This is a bit lower than the person in the worked example, but not dangerously low)

More Information!

Want to know more about density?

Find Out More >

Data Analysis

The table below shows predicted values of bone density for an astronaut who spends five years on the International Space Station. The first measurement was taken before arriving at the space station (ie. when the astronaut was still on Earth):

Draw a graph to show the trend in bone density over time

If you needed to draw a graph to show the trend in bone density over time, would you plot time or bone density on the horizontal axis?
time (this is the independent variable; it doesn’t depend on anything – this always goes on the horizontal axis)
Which variable (ie. time, or bone density) would you plot on the vertical axis?
bone density (this is the dependent variable; the density of the bone depends on how much time the astronaut has been in space. The dependent variable always goes on the vertical axis)

Now, using graph paper, draw your graph, starting with the axes