AIMS: To produce a set of meaningful data to inform experimental results. To prove that even small objects can cause serious damage if they are moving fast enough. That an object's kinetic energy is related to its mass and speed.

OVERVIEW: The last experiment enabled you to see that there was a relationship between the size of a crater, and the mass and speed of the "meteorite". This module aims to give you the tools to actually calculate the energy that a moving body has, and to show that even microscopic particles can present a hazard to the space station.

MATERIALS: Gelatin powder, straight-sided clear plastic beaker or measuring jug (15 cms deep at least ), centimetre scale, metre scale, measuring tape, step ladder, graph paper, 8-10 equally-sized ball- bearings.

EXPERIMENT: 1. 24 hours beforehand, make up the gelatin in the beaker/jug. Note that you may want to make three loads, one according to the instructions, and the other two with progressively less water in them (about 350 ml. to one pack may work well, but that depends on the pack). Cover the gelatin with food wrap and leave it to set overnight. 2. Make a centimetre scale and tape it carefully to the side of the jug. 3.Drop a ball-bearing into the gelatin from a height of 25 cms. Record how far it sinks. Repeat for heights of 50, 75, 100, 125, 150, 175 and 200 cms. Record all the depths.

INVESTIGATION:

1. As the height increases, what happens to the depth the bearing sinks into the gelatin?

2. What factors can affect the depth?

3. To get real data, we need to make our figures mean something. So the first thing we do is weigh the eight ball-bearings together, and divide by eight, to get the mass, m, of one ballbearing.

4. To get the velocity, v, of the ball-bearing, falling from a height, d, of 150cms, with the acceleration, a, being 980 cm/sec^-2, use the following formula: v=root 2ad.

5. To get the kinetic energy, or energy of movement, of the ball-bearing at the point of impact, use this formula: KE =1/2mv², putting in the figures for m and v that you have found.

6. An object has potential energy by virtue of its height. When it starts to fall, this becomes kinetic energy. Again, taking the height to be 150 cms, use the followuing formula to get the ball-bearing's potential energy. PE = m x g x h.

7. Now look at your figures for your experiments. How does the depth of the ball-bearing compare with its kinetic energy? Plot a graph of kinetic energy (ergs) on the x-axis, and depth on the y-axis. Then plot another graph with impact speed (cm/s) on the x-axis, and kinetic energy on the y-axis. What do you notice about the two graphs? Which one shows the importance of velocity in these calculations?

8. A very small meteoroid travelling very fast can cause more damage than a more massive object which is moving more slowly. For example, which has the greater kinetic energy, a grain of 0.2 gm sandgrain moving at 9000 metres per second, or an 8 gm pebble travelling at 400 metres per second? Use the formula for kinetic energy. Are you surprised by the results?

In space, meteoroids travel at speeds between 11 and 72 kms/sec; orbital debris orbits the Earth in low orbits at relative speeds between 1 and 14 kms/sec, depending on the height of its orbit. Which orbit will give the greater velocity/ Why do you think this is? Can you find out in which direction most of the debris is moving? What are the implications for the space station?

What danger do you thnk the space station is in.

What steps do you think you could take to protect the space station and its occupants from the possible danger of micrometeoroid impact? Remember, any protection has to be light in weight. You might want to research into bulletproof vests.

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