Purpose: To help build on the idea that it is not only the weight of an object but also its size that influences the difficulty of a lift. Have students lift objects of various sizes and weights and emphasize proper lifting techniques.
Suggested objects to lift include:
- Several text books (small and heavy)
- The same pile of books, placed on a tray
- Empty box of similar size to the pile of text books (small and light)
- Roll of posters (long and light)
- Chair (medium weight, awkward)
Ask the student to record how much effort it takes to lift these objects.
What should the students observe?
The learners should notice that the easiest way to carry an object is to hold it waist high and as close to the body as possible. Any time you cannot hold the object in this position, the amount of effort required increases.
In this example, the chair feels heavier to lift than its actual weight because the learner likely has to hold his/her arms away from his/her body in order to lift it. The pile of books is heavier to lift when on the tray because the learner's arms are forced away from his/her body.