Tuesday, 28 April 2015

Fatigue, lactic acid build up and recovery time

Equipment

Stopclock

Method

Start the stopcock and clench and unclench hand fully as rapidly as possible until the burning sensation becomes too great. Stop the stopcock.
Wait for 1 minute then repeat the test.
Increase the wait time by 1 minute and repeat again, and continue up until a 10 minute interval between exercises.

Produce a plot of interval between exercise vs time to onset of fatigue.


Exercise rate, breathing rate and fatigue

Equipment

Treadmill
Spirometer
Stopclock

Method

Place the spirometer mouthpiece in the test subjects mouth and clip their nose so all air goes through the mouth.
Get the person on the treadmill and slowly increase speed until it reaches 4m/s. Time how long it takes for the person running to feel fatigued and unable to carry on. They should then lift off the treadmill by pushing up on the sides and the treadmill should be slowed.
Repeat at intervals of 0.5m/s up to 8m/s.
The spirometer reading can give an indication of the breathing rate and volume during the test.

The runner will need adequate time for recovery between tests.
The runner will also need to be provided with an glucose drink prior to the experiment to ensure that  blood sugar levels do not affect the onset of fatigue.


Wind turbine blades numbers vs output voltage

Equipment

Hairdryer
Clamp & stand x 2
Motor/generator
Connecting leads
Voltmeter
Ruler
Stiff card
Compass
Glue
Scissors

Method

Using the compass mark a circle of 12cm diameter on the card and another of 3cm diameter in the middle, then cut out the large circle.
Mark points around the edge of the circle at the 12, 3, 6 and 9 o'clock positions, mark again at the midpoint between these, and again at the midpoint between the last set of points. You will have 16 points marked around the edge. Use a ruler to mark a line joining opposite points.
Attach the centre of the circle to the motor/generator spindle firmly using glue.
Cut from the edge to the inner circle at the 12 and 6 o'clock positions to make a turbine with 2 blades - you may need to gently curve the card.
Attach the wind turbine to the clamp stand, with the hairdryer in the other so that there is 10cm between the hairdryer nozzle and the turbine blades.
Connect the turbine to the voltmeter.
Turn on the hairdryer and record the reading shown on the voltmeter.

Adjust the turbine blades, cutting it so that it now has 4 evenly spaced elements. Repeat the measurement of the output, ensuring that the distance o the hairdryer remains at 10cm.

Repeat twice more, with 8 blades and 16 blades on the turbine.

Safety

The hairdryer may get hot after prolonged use. The turbine blades could get caught up in long hair, so it should be tied back.



Wind speed & electricity generation

This experiment will let you investigate how wind speed affects the amount of electricity produced by a wind turbine.

Equipment

Fan attached to variable power supply (0-12V)
Motor/generator with fan blades attached
Voltmeter (0-5V analogue)
Connecting leads
Clamp & stand
Metre stick.

Method

Place the fan on the desktop.
Mount the turbine using the clamp and stand so that the centre of it is in line with the centre of the fan ensuring that the blades can rotate freely.
Make sure that the fan blades and the turbine blades are 10cm apart.
Connect the turbine to the voltmeter.

Adjust the setting on the power supply up by 1V at a time until the turbine blades start to spin.
Record the reading on the voltmeter.
Continue to increase the setting on the power supply by 1V at a time and record the reading on the voltmeter.

Safety

Spinning fan blades can cause damage. Fingers should be kept clear as should long hair or any loose clothing. Ensure the clamp and stand is stable, if you need to mount the generator high on the stand then you may need a g clamp to secure it to the bench.

Sunday, 26 April 2015

Comparing antibiotic effectiveness

Different antibiotics work in many different ways to kill bacteria, but not all antibiotics work on all bacteria.


Equipment

Poured plates containing different bacteria types (1 type per plate)
Solutions of different antibiotics
Filter paper discs
Tweezers
Ruler

Method

Number the disks with a pencil.
Soak discs numbered 1 in the first solution, 2 in the next etc.
Place a disc numbered 1 on the agar in each plate.
Repeat with the other discs.
Place the lids on the dishes, tape down in 4 places. Do not open the plates again.

Incubate for up to a week to allow the bacteria colonies to reproduce and become visible.

Measure the distance from the edge of each disc to the nearest bacteria colony.

Compare the data to see which antibiotic affects which bacteria type the most.

Safety.

All equipment should be kept sterile. Wash your hands before and after using an antibacterial hand wash - gloves may also be worn. Plates will need to be autoclaved once they have been examined.

Investigating antibiotic properties

This experiment investigates how some common household items can work as antibacterial agents.

Risks

Any experimentation with living bacteria requires strict aseptic technique. It is assumed you will be familiar with these techniques prior to completing this experiment - if not advice can be found at http://www.microbiologyonline.org.uk.

In general ensure that hands are washed before and after completing any work with bacteria and that all implements used are sterile. Additionally plates should not be opened once incubated and should be disposed of in an autoclave.

Method.

Use a poured plate with the bacterial strain being used already present in the agar.

Select a number of household items, such as hand soap, dish soap, bleach, mouthwash and use forceps to dip a small disk (up to 1cm diameter maximum) into the liquid and place on the surface of the agar. A disk dipped in boiled water should also be used as a control. To allow easy identification use a pencil to number the disks prior to dipping.

Set up three plates in exactly the same way, then leave to incubate for up to a week.

Measure the furthest distance from the edge of each disk to the bacteria now visible to determine the most effective antibacterial substance.

Metals, acids, reactivity and energy

Reacting metals with an acid produces Hydrogen gas. These reactions are also exothermic, the energy released in the reaction is related to the relative reactivity of the chemicals used.

Equipment

Samples of powdered metal.
Hydrochloric, Sulphuric and Nitric acids - 1 molar
Boiling tubes
Top pan balance - 0.01g resolution
Digital thermometer - 0.1 degree C resolution
Measuring cylinder - 10 ml

Method

Measure 10ml of acid into the boiling tube.
Measure 0.5g of the metal powder.
Record the temperature of the acid using the digital thermometer, then add the metal powder to the acid.
Record the highest temperature reached.
Repeat for each metal, with each acid.

Risks

Some reactions will produce a lot of energy and get very hot so care should be taken when touching the bottom of the boiling tube. The reaction evolves Hydrogen gas which can cause the liquid to bubble up the boiling tube and spill over. care should be taken when clearing up spills. Goggles should be worn at all times during the experiment.

Metal Reactivity with Acid

The purpose of this experiment is to investigate the relative reactivity of a variety of metals. Extension ideas are provided to allow generalisation across acids and to also investigate the effect of acid concentration.

The more reactive a metal is, the faster it should react and thus the quicker it should evolve a set volume of Hydrogen.

Equipment

50ml measuring cylinders
Top pan balance with 0.01g resolution
Stop clock
Powdered samples of 4 different metals (e.g. Magnesium, Zinc, Copper, Iron)
Hydrochloric Acid
Conical flask
Bung with delivery tube
Water trough
Goggles

Method

Note - you will need to perform a preliminary test to find a suitable volume and concentration of acid and mass of metal to use to ensure a sufficient volume of gas is produced.

Set up the water trough with the 50ml measuring cylinder upturned to collect the gas produced over water.
Measure out your acid and place in the conical flask. Weigh out your metal powder and set to one side.
When you are ready tip the metal powder into the acid and place the bung with delivery tube into the conical flask, then start the stopclock.
Time how long it takes the metal to produce 25ml gas.
Repeat the test twice more, then repeat using a different metal.

To ensure that the effect you are seeing is just down to the metal you will need to ensure that some control variables are maintained. The mass of metal used, volume of acid used and concentration of acid used should all be the same. Additionally the metal powders should ideally have the same size of grain. Finally you should also try to control the temperature. There will be a heating effect due to the reaction and this in turn affects the rate at which the reaction occurs.

Safety

Do not use highly concentrated acid for this experiment as spills may cause damage to surfaces or burns to skin. Goggles should be worn at all times when working with liquid chemicals. The reaction produces Hydrogen gas which is explosive, so care should be taken that no naked flames are present during this experiment.