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.

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.

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.