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SCIENCE

GRINDING CHALK

Objectives

  • To investigate methods of grinding chalk to produce a powder.
  • To appreciate the use of grinding as a method of creating powders in industry.

Curriculum links

English National Curriculum: Science 1: 1b, 2c, 2d & 3: 3a

Gateway story

Grinding is an important process within the colour industry, ranging from grinding raw materials through to grinding lumps of coloured pigment after being 'baked' at high temperature. Grinding occurs on a small scale in the laboratory and on a large scale in the production areas.

Gateway elements

This gateway consists of:

  • Pestles and mortars
  • Large scale grinding equipment
  • Animation.

Pestles and mortars: Both automated and hand-held pestles and mortars are used in the colour industry's laboratories. They are used to grind small samples of pigment for testing.

Animation: The chameleon takes a heavy-footed approach to grinding!

Approximate time required: 60 minutes

Resources needed

Per group:

Grinding Chalk sheet
Packet of chalk sticks
Sieve
Tea-strainer
Pestle & mortar
Plastic food bag
Rolling pin
Grater
Plastic jar or bottle (e.g. 250 ml pop bottle)
40 - 50 marbles or small stones (enough to fill about half the bottle)
Stop watch/clock.

SAFETY NOTE

Children should not grip the chalk stick too close to the grater (say, 1 cm, or a 'thumbnail' away).

Suggested organisation

Children can try this activity as part of a circus of related activities where they move on, in mixed ability groups, from one to the next in rotation.

Carrying out the activity

The class are given copies of the Grinding Chalk sheet. Ask them to discuss:

  • the merits of the different grinding options listed
  • an additional method, if they feel they have a good idea
  • criteria required for an 'effective' grinding method
  • the methods they feel offer the best grinding options.

Decide how many grinding methods each group will test. This choice will depend upon the equipment and time available, and the teaching approach taken (e.g. circus of activities, whole class teaching).

The children then consider ensuring a fair test, including the measurement of variables. Children of this age should be encouraged to state more than 'we will use the same amount of chalk'. They should be able to state the quantity of chalk they will use, and the reason why keeping this the same is important. For example, if measuring the time taken to grind the chalk, the amount of chalk ground is important, in order to compare the times taken for different methods. However, if the time taken to grind the chalk is not considered important, but simply the quality of the powder, then the amount of chalk used is relatively unimportant.

Children may choose to measure the quality of the chalk powder, by passing it through a sieve and/or a tea-strainer.

The table provided for children to record their results has been left open-ended to some extent, to allow for different measurement options.

Background information

Grinding is a process which is used extensively in the colour industry. It is used to grind ingredients which arrive in solid forms and it is used to grind pigments after they have been baked in large ovens, when they need to be broken down from bricks or large lumps into powder.

One of the most common grinding methods used in industry uses a large rotating drum which is filled with stones.

Extensions / links

Science
Children can design their own investigation into the best methods to use to turn other materials into powder, e.g. granulated sugar into icing sugar.

Science
Hand lenses can be used to examine a range of commonly used 'powders', such as sugars, flours of different kinds, talcum powder, salt, etc. to make observations on the similarities and differences.