talking about science: floating and sinking … the edges of the tube, a little roughness actually...

Talking about science: Floating and Sinking

FEAST workshop – Talking about science -‐ science center NEMO – 6 November 2012 1

EXPERIMENTS TO TRY AT HOME Did you and your child enjoy experimenting together today? Are you both thirsty to do some more experiments? Then this hand-out may be helpful! It’s very likely that not all your questions have been answered, or perhaps some steps or experiments weren’t completely clear. Most answers will lead to more questions, and this is a normal part of the learning process. We want to give you a few tips and suggestions to take home with you so you can continue your experiments with the subject of sinking and floating. Always remember that there’s not really a ‘wrong’ or ‘right’ way to experiment: the point is to keep on asking questions! THINGS YOU WILL NEED:

• Clear plastic container. Water is heavy, so it has to be strong. Simple storage boxes work really well. Plastic has the advantage of being cheap and light weight, and you can quite easily make a hole in the side if you plan on making an overflow to measure water displacement. We recommend a volume of at least 10 liters.

• A digital or analog scale, with at minimum 1-gram precision. A kitchen scale works very well. If you can’t reset your analog scale after putting on your empty cup or bowl, you can use tape or a pen to mark the ‘zero’ weight position.

• A beaker or measuring cup to catch displaced water. You can also use a bowl or cooking pot. • A small tube for your overflow. Non-flexible electrical tubing is a good choice. Make sure it is not

too small, a diameter of at least 1 cm should be sufficient. • Construction materials (string, tape or glue, scissors). Useful to combine different types of

materials into one object to experiment. Clay can also be used as a material to make watertight seals.

• Paper tape and/or a marker to mark the water level in your container. • Objects to test out! Be as creative as you want to and try to surprise yourself. Try to test things

that you can manipulate or alter so that you can change its buoyancy. Things like plastic soda or shampoo bottles are excellent because you can empty and close them, and then fill them with water to make them sink. Test objects of which you don’t know it they will float or sink, but also objects of which you are absolutely certain how they will react. You may find the results can be surprising!

• Clay is a really good material if you want something flexible: it’s cheap, fun for kids, it sinks on its own but can be easily manipulated and reshaped.

• Different fluids to make things float in. A bit more tricky, but cooking oil is relatively cheap and available, and safe to play with. You can also change the density of water (and therefore its buoyancy) by adding and dissolving salt.

• Pen and paper to write down your results.



MAKING A CONTAINER WITH AN OVERFLOW

1. To investigate the amount of water displaced by an object you will need a container with an overflow. A plastic container is very suitable.

2. Carefully use a sharp knife to make a hole in the side, about three quarters from the bottom. The hole should be a little bigger than the tube you plan to use, so just over 1cm diameter. If you are not sure how to make a hole, ask someone who is good with tools to help you.

3. Experiment with how you orientate the tube. We found it works best to make an angle of about 45º, with the exit of the tube pointing down towards your cup and scale. Don’t sand or smooth the edges of the tube, a little roughness actually works better to ensure reliable water flow.



4. Use clay on the inside and outside to make a watertight seal around the tube.

5. Now fill the container with water. Make sure you have enough space under the overflow to place a scale and a bowl to collect water.

6. Fill the container until the water starts to flow through the tube. Now wait until the water stops dripping completely. Be patient! Remove the water from the bowl or beaker, reset the scale to zero and you are ready to experiment!



7. From now on, be very careful when handling the experiment. Any disturbance of the water will cause some to overflow and this will make your results less accurate.

8. After measuring each object, always return the water to the container (step 5 and 6), making sure the water is level with the tube entrance.

THINGS YOU CAN INVESTIGATE: In our workshop and experiments we have tried to figure out why objects float or sink. This has resulted in a general principle (Archimedes’ Principle) that allows us to make predictions. Once we are comfortable with our understanding of these ideas it becomes interesting to ask more complicated questions. Below we give a few suggestions to start with, but the possibilities are virtually endless!

• We have done most of our experiments with water, and one with cooking oil. Using your new knowledge and testing method, can you explain why the water balloon floated in water but sank rapidly in oil?

• We have seen situations where the displaced water weighed less or exactly the same as the object. What would happen if the displaced water weighed more than the object? Can you imagine a situation where this would be the case?

• Can you explain how a submarine works? How is it that a submarine can change its buoyancy, or: how does it dive and resurface?

• Archimedes’ Principle can also be applied to gasses. Try to imagine a balloon and see if you can figure out why and how they float through the air. What is special about helium and hot air balloons?

• A brain bending question: imagine you are in a swimming pool. In the pool, a rubber boat is floating on the surface. In the boat lies a large and heavy brick. Now we take the brick out of the boat and drop it in the water. It of course sinks to the bottom of the pool. What happens to the water level of the swimming pool?

• The human body has an average density that is almost exactly the same as that of ordinary water. You can experiment with this the next time you are going swimming. Take a deep breath, hold it, and try to stay as still as possible not using your arms or legs. You will find out that you will slowly rise to the surface: you’re floating! Now release all the air from your lungs….. What can you feel happening? Can you explain it?

• Now you know that human body parts have the same density as water, can you figure out a way to measure the weight of just your head, arm, leg or any other part of your body?

• Ice is just frozen water. But if it is the same material, why does ice float in water? Will it float in other liquids as well?

• If you use a measuring cup or beaker to collect the displaced water, you can make accurate measurements of both weight and volume. With these two properties you can determine the density of objects and materials. Make a list of the densities of all the objects and materials you have experimented with and arrange them in order. Also calculate the density of water.



CONSIDERATIONS FOR PARENTS: When playing and experimenting with your child it is important to keep a few things in mind:

• The purpose of our workshop is not to teach specific facts or knowledge. The purpose is to learn how to experiment and challenge your own ideas. We have seen that everybody is continuously making their own ‘scientific theories’, this is a natural part of learning. Most of these ideas are not formal and based on experience. If we want to challenge or improve on our current ideas, it is important to first figure out what those ideas and informal theories are.

• This can be done by asking questions like the one we saw in our workshop. Ask your child to make a prediction about a certain phenomenon, and then ask why he or she thinks a certain result will happen (“I think the block will sink because…”).

• It is very important not to correct or value the ideas your child comes up with at this time, although you can help in rephrasing or simplifying the initial predictions.

• When you do the experiment, the child will either see his theory confirmed or challenged. Now you can see if the theory needs any adjustments and make a new prediction.

• The parents’ role is to guide the child through these steps, not to take the steps for them. • The concepts of ‘right’ and ‘wrong’ answers are not really relevant (at this moment). The point is

to make explicit your informal theories and challenge them. Even ideas that are technically incorrect can lead to new knowledge. As long as you keep experimenting and asking questions, there’s really no way you can ‘fail’ in science!

• Always be honest. If your child asks a question to which you don’t know the answer, say so. This will be a starting point for new questions, new predictions which can be experimented with. Every child has a natural curiosity and drive to always ask more questions, so it is pretty much inevitable that this situation will happen. Then try to think of questions that can help you fill in gaps in your ideas and theories. Make use of internet, schools, libraries, teachers, museums, anything you can think of to gain more knowledge.

• We have focused on the parent-child relationship, but the ideas can be applied to other groups as well. You can stimulate your child to experiment and play with friends, or at school. The general principle of making a prediction (hypothesis), experimenting, challenging and adjusting your ideas can be used in any situation!

talking about science: floating and sinking … the edges of the tube, a little roughness actually...

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