Wednesday, 4 June 2014

Centre of mass & stability

Equipment

2 litre straight sided plastic drinks bottle with lid
Ruler
Protractor
Water
Wooden board with wooden lolly stick glued on

Method

Place the empty bottle on the wooden board so that the edge of the base buts up against the lolly stick so it does not slide.
Align the centre of the protractor with the edge of the board and slowly raise the opposite side so that the bottle starts to lean.
When the bottle falls read off the angle on the protractor. Repeat this at least twice more.
Add 5cm depth of water to the bottle using the ruler to measure.
Screw the lid on again tightly and repeat the tipping and recording of the topple angle.
Continue to add 5cm dept of water and repeat the tipping until the bottle is full.

Plot a graph of water height vs toppling angle. Why does it have this shape?

Risk assessment

Ensure lid is screwed on tightly when carrying out this experiment. Any spills should be mopped up straight away. As the bottle fills it will become heavier and could hurt feet if it rolls off the table, to reduce the chance of this happening carry out the experiment in the middle of the table and have a second person ready to catch the bottle as it falls.

Energy released from fuels

Equipment

Spirit burners with different fuels in (e.g. Ethanol, Propanol, Butanol)
Top pan balance (0.01g accuracy)
Boiling tube
Clamp and stand
Thermometer
Stopclock
Measuring cylinder
Goggles

Method

Place 50ml of water into the boiling tube and place into the clamp. Measure the water temperature.
Place spirit burner on the balance and record the initial mass.
Next place the spirit burner under the boiling tube, light it and start the stop clock, ensuring that the tip of the flame is just beneath the boiling tube.
After 2 minutes have passed snuff out the spirit burner and record the temperature of the water.
Place spirit burner on the balance and record the final mass.
Repeat this twice more using a fresh boiling tube and fresh water and then calculate the average temperature rise divided by the average change in mass.
Repeat the whole experiment three times for each fuel.

Risk assessment

Care should be taken with the spirit burner to ensure you do not spill any fuel. Goggles should be worn when heating liquids. When replacing the boiling tube take care as it will be hot - it should be left in a test tube rack to cool slowly so as not to crack the glass.

Plant growth and crop density

Equipment

Sunflower seeds
Plot of soil 10m long and 50cm wide
Metre stick

Method

Mark out 5 points in the centre of the width of the planting bed that are 2 m apart.
Around each point mark a 10 square centimetre box.
In the first box plant one sunflower seed, two in the second etc until there are five seeds in the last box.
Water in all the seeds and continue to water every couple days.
Ensure when choosing the planting direction that the plants in one box will not cast a shadow on the plants in another box as they grow.
Allow the plants to grow for one month and then record the height of each plant.
Where there is more than one plant in a box work out the average plant height.

Risk assessment

Ensure hands are washed after working with soil.

Temperature and rate of reaction

Equipment

Water bath
Sodium Thiosulphate solution
Hydrochloric Acid
Measuring cylinders
Boiling tube
Test tube
Led torch
Light sensor & datalogger
Thermometer
Clamps and stands
Goggles

Method

Add 10ml of the Sodium Thiosulphate solution to the boiling tube and place in the water bath set to 25 degrees C.
Add 5ml of the acid to a test tube and also place this in the water bath.
Set up a clamp and stand to hold the boiling tube with the LED torch on one side of it and the light sensor on the other. Set the datalogger to measure light intensity vs time.
When both liquids are at the correct temperature take them out of the water bath, fix the boiling tube into the clamp stand between the torch and the sensor, so that the sensor is against the tube and the light shines through the liquid then tip in the acid.
When the light intensity measured stops changing stop the datalogger.
Repeat the experiment using temperatures of 30, 35, 40, 45 and 50 degrees C.

Risk assessment

Be careful when clamping the boiling tube so that it does not get crushed. Clear up spills straight away. Goggles should be work when pouring liquids.


Monday, 2 June 2014

Polymer strength testing

Equipment

Clamp and stand
Slotted masses (100g) and hanger
Strips of plastic bag of different widths (1 to 5cm in 1cm intervals)
Sticky tape
Ruler

Method

Take a strip of plastic bag and use the tape to secure the end into a loop.
Hang the loop with the taped end over the clamp and secure the loop using some more tape. Use the ruler to measure the unstretched length of the bag.
Add the masses 100g at a time until the loop breaks or until you reach 1kg and record the mass. If you reach 1kg without the loop breaking measure the length to which the loop has now stretched.
Repeat this three times for each width of loop.

Risk assessment

The bag can break suddenly so care should be taken to stand clear when adding masses so that they do not fall onto the floor and land on the feet of the experimenter. The experiment should be set up in the middle of a table so that it does not risk tipping over . The Bag loop should be suspended over the base of the stand to ensure the experiment remains stable.


Rate of reaction, concentration & temperature

Equipment

2cm strips of Mg ribbon
Different concentrations of Hydrochloric acid (0.1, 0.5, 1 and 2 molar)
Test tubes
Test tube rack
Measuring cylinder
Thermometer
Stopclock
Goggles

Method

Place 10ml of the first concentration of acid to be used into a test tube. Place in the thermometer and record the temperature of the acid.
Drop in one of the Mg ribbon strips and start the stopclock.
Observe the reaction, looking for gas being produced. When the reaction stops stop the stopclock. If there is any of the Mg ribbon left this should be noted in an observations column. Note the end temperature.
Repeat this twice more using the same concentration of acid. Repeat the whole process of three tests with each different concentration of acid.

Safety

Goggles should be worn throughout the experiment. Spills should be mopped up straight away. Extra care should be taken when handling the most concentrated acid.

Analysis

The rate of reaction is affected by both concentration and temperature. Does the heating effect of the reaction affect it's rate? How could the above exepriment be adapted to eliminate the heating effect of the reaction and that there may not be enough reactants to complete the reaction?


Thursday, 29 May 2014

Centripetal force vs speed of rotation

Equipment

Glass tube 15cm length with ends flamed so that they are smooth.
1.5m length of string
Hooked mass hanger for 100g slotted masses
Large rubber bung with home through centre
Marker pen
Stopclock

Method

Tie the bung to one end of the string. then measure 60cm from the centre of the bung along the string and make a mark with the pen.
Run the string through the tube and tie a loop at the end to hang the masses from.
Hang the mass hanger and spin the bung at the correct speed to keep the pen mark at the top of the tube.
Start the stopclock and time how long it takes for 10 swings of the bung. Take two more readings of the time for 10 swings to calculate an average and check for anomalies.
Add a mass to the hanger and repeat the swinging and timing being careful to ensure that the pen mark stays at the top of the tube. It is important that the radius of the swing does not change as this is another factor that affects the centripetal force needed and so will affect the speed you measure.
Continue adding masses and timing 10 swings until you have 500g on the hanger.

Calculate the centripetal force applied by multiplying the mass used by the gravitational field strength.
Calculate the average speed by taking the circumference of the circle the bung travels in and dividing by the average time for one swing.

Plot a graph of centripetal force vs speed of motion.

Risk assessment

Ensure you are working in a clear area before starting to swing. After each repeat check the string to make sure it is not beginning to fray. There is still a risk of the string breaking and the bung flying free. As such only rubber bungs should be used. Do not attach a metal mass to the swinging end. Goggles should be work to protect eyes from any possible flying bungs. As you are using a glass tube care should be taken not to grip it too tightly as this increases the chance of the tube breaking. The tube should also be well supported at the rotating string end to prevent any extra stress on the tube increasing the risk of it breaking.