Wednesday, 10 October 2012

Viscosity of oils

Information

This method uses an instrument known as a cup viscometer to measure the viscosity of a fluid.  A cup viscometer is essentially just a smooth sided cup with a hole in the bottom. A preliminary experiment may be required if you are making a cup viscometer to determine the correct volume of oil and hole size to use. You need to be able to use the same cup for all your oil samples and it should be set up such that the oil does not drain so quickly it is difficult to time, nor that it takes so long as to be impractical to complete multiple tests in a reasonable period of time.

Equipment

Clamp and stand
Cup viscometer
Bung for hole in viscometer
Collecting beaker
Measuring cylinder
Stopclock
Samples of different oils

Method

Set up the viscometer in the clamp and stand so that the beaker can be placed below it and you can see the oil flow.
Place a known volume of oil into the viscometer with the bung in the hole.
Place the collecting beaker under the hole.
Start a stopclock as you remove the bung and wait for the oil to drain.
When the oil has finished draining stop the clock and record the time.
Repeat twice more for this oil sample and repeat the whole process for each oil sample to be tested.

Sometimes very viscous oils will start to drip during the final parts of draining. If this is the case it is suggested that you time until each oil first starts to drip.

Try to ensure that the room temperature and thus oil temperature remains constant as the temperature of the oil affects the flow rate.

Energy stored in food 2

Equipment

Bunsen burner
Clamp & stand
Metal tin
Cork & pin
Measuring cylinder (25ml)
Datalogger and temperature probe
Top pan balance
Food samples

Method

Set the metal tin up above the cork and pin using the clamp and stand to hold it in place.

Add 20 ml of water to the tin and place the temperature probe, connected to the datalogger, into the tin.

Measure out 5g of the food sample and attach to the pin. Start the datalogger, get the food sample burning and ensure it is placed directly under the tin. Use the datalogger to record the maximum temperature of water reached.

Empty the tin and repeat twice more with fresh water for the first food sample. Repeat the whole process for each food sample you have.

Use the data from the datalogger to analyse how much energy is contained in each food sample. The larger the temperature rise the greater the energy contained within the food. You may also look at the graph the datalogger produces to determine the rate at which this temperature rise occurred.

Choice Chambers 1 - Light & dark

Equipment

Choice chamber
Paper to black out half of the choice chamber
Woodlice (At least 10)
Container to store woodlice with bark/leaf mould

Method

Set up the choice chamber so that half of it is dark and half of it is open to the light. Taping paper to the lid, base and around the sides may be a good way to do this.

Introduce a known number of woodlice, at least ten, to the center of the choice chamber and replace the lid, ensuring the covered halves line up.

Start a stopclock and on the minute for ten minutes count the number of woodlice in the exposed half. Note down any behaviour you notice too, for example how far into the light half do the woodlice tend to go.

Repeat the experiment three times, if possible with different woodlice.

Ensure at all times that you are extremely careful with handling the woodlice and that they have as natural an environment as possible when not within the choice chamber. Also ensure you thoroughly wash your hands after the experiment has been concluded and you no longer need to handle the woodlice.

Monday, 8 October 2012

Energy stored in food

Equipment

Boiling tube
Thermometer
Clamp & stand
Cork and pin
Measuring cylinder (25ml)
Bunsen
Goggles
Top pan balance
Flammable food samples

Method

Set up the clamp and stand to hold the boiling tube a known distance above the cork and pin to ensure the same level of heat flow into the boiling tube with each test.
Measure out 20ml of water and place it in the boiling tube and clamp into place.
Add the thermometer to the tube and note the water temperature.
Find the mass of the food sample you are using, note this down and then place it on the pin.
Light the food sample and then quickly position it under the boiling tube.
Once the food sample has finished burning record the temperature of the water.
Repeat three times for each food sample with fresh water.

Safety

Be careful of all hot materials, such as the pin and boiling tube. If the water temperature has raised significantly collect a fresh boiling tube rather than putting cold water in to a hot tube as it could shatter.

Analysis

Work out the temperature rise and multiply this by 84J per degree to get the energy transferred. Divide this answer by the mass of food sample used to find the energy per gram of food.

Hard water testing method

Equipment list

Measuring cylinder (10ml, 50ml)
Boiling tubes
Bungs to fit boiling tube
Rack
Stopclock
Ruler
Soap solution
Selection of waters to test.

Method

Measure out 25ml of water to be tested and pour into the boiling tube.
Measure out 2ml of soap solution and add to the boiling tube.
Insert the bung and put your thumb over the top.
Use the stopclock to time vigorously shaking the tube for 15 seconds.
Place the tube into the rack and note the height of the foam formed from the water surface to the top of the lather.
Repeat three times for each water sample to find a mean.

Safety

Ensure the bung does not slip out during the shaking. This could go into the eyes or could leave a slip hazard. Should any tubes be droped and broken any spills should be cleared up straight away.

Results

The hardest water should produce the least bubbles and also produce a soap scum (Calcium Stearate)


Water hardness - bulk test


What is hard water?

 The hardness of water has a direct effect on the ability to form a lather when mixed with soap. This means that you will end up using more soap to achieve the same froth and get the same cleaning effect as in a soft water area. It also leaves a soap scum which does no occur as much in softer water areas. Typically soft water is found in areas such as Cornwall where the underlying rock is granite. In areas such as Hampshire the the water passes through chalk deposits on its way to aquifers, and this is where the additional calcium ions that make the water hard are picked up.

Testing for water hardness.

As indicated above, testing for water hardness is relatively simple. All you need is a sealable and see through container such as an empty drinks bottle. Half fill it with water and add a few drops of washing up liquid, close the lid and shake vigorously. The less foam produced and the more milky looking scum on the surface the harder the water you have.

Some forms of hard water can be 'cured' by boiling the water, but this only works if the Calcium present is in a hydrogen carbonate form. Other sorts of calcium salts mean that the water is permanently hard and will not be softened by boiling.

Pendulum length and period

Equipment

Clamp & stand
Cotton or string
Plasticine
Stopclock

Method

Depending on the height of your stand set the range of lengths of string you will test - 5 to 50 cm is a suggested value.

Clamp the string at the desired length and raise the pendulum, keeping the string taut.

Release the pendulum and start the stopclock. Time how long it takes for 10 swings to complete, remembering that one swing is a complete motion from left to right and back to the left again. Timing 10 swings (or more if you wish) will help reduce the error per swing.

An alternate method to improve the timing would be to set the pendulum up with a light gate and datalogger, so that the pendulum bob breaks the beam of the light gate. This would only time one swing.

Take three or more sets of results for each length to enable errors to be spotted and eliminated when you calculate the mean value for one swing at each length.

This experiment is generally safe, with the only real hazard being knocking over the clamp stand. This can be avoided by placing it in the middle of the bench, or alternatively using a g-clamp to secure it. It is advised that large mass bobs are not used as this will also affect the stability of the experiment.

Finally plot your results on a graph. If you have time you may wish to play a second graph of bob length against period squared - this second graph will end up as a directly proportional line if you have made your measurements carefully enough.

Damping of pendulum motion

Introduction

This experiment aims to find the relationship between surface area of a pendulum bob and the time taken for the pendulum to come to rest.

Equipment

Clamp & stand
Fine wire or fishing line
Pendulum bobs of differing cross sectional area (spherical or cylindrical bobs will work best)
Stopclock
Ruler

Method

The pendulum should be set up with a known length of wire, e.g. 50cm between pivot and the centre of mass of the bob.

The bob should be raised to one side such that it is elevated 10cm from its rest position and the line is taut.

As the bob is released the stopclock should be started and the pendulum should be observed until it comes to rest, at which point the stopclock should be stopped and time recorded.
The experiment should be repeated three times with each bob.

Care should be taken to ensure that the centre of mass is at the same distance from the pivot so that the effective length of the pendulum remains constant.

Analysis

The cross sectional surface area of the bob should be plotted against the time taken for the bob to come to rest.