I can't see a force - so it isn't there
Teaching Guidance for 5-11 11-14
Wrong Track: How can the table push up on the book? It's not alive is it?
Right Lines: A force can be exerted by any object whether living, dead or never lived.
Thinking about the learning
Pupils are often unable to associate a force with an inanimate object. People can apply a force to objects – they make a decision to lift a bag of shopping or to push a motor car. However what about a book resting on a table? How can the table be forcing the book? The table is not alive. This is indeed a tricky situation. There is no easy practical activity which can immediately unravel this dilemma. However, a useful way of thinking about and explaining support forces is presented at the start of episode 02.
Here are some children trying to identify forces. These clips are worth watching several times. Particularly interesting, at this stage, is to think about how you can put them in a position where they can work out how to identify the forces, rather than just telling them the answers.
A force is what is known in science as a vector quantity. To communicate the idea of forces, learners are expected to annotate diagrams using arrows. To build confidence in doing this it is important to offer learners an experience with a number of force-related situations. Invite learners to explore the language of forces, and experiment using force arrows. There are teaching activities here designed to support such learning.
Thinking about the teaching
Being able to see that a force is acting and also where a force is acting is a skill to be developed. Being able to identify, describe and label forces is part of being able to model the real world as a scientist might. Learners need to be given the key to a language which will help them to describe forces. Here are three guiding principles:
- The first is that in every situation they meet, the vertical force due to gravity is present. Many start their description with this force.
- Secondly, look carefully at the selected object. It will be interacting with local things in its environment, and perhaps with other things not so close. Each of these kinds of interaction will be replaced with a force arrow. Use the kinds of interactions to identify the force arrows.
- Finally, the phrases
exerted byare critical to talking about forces. For example:
a force exerted by that thing acts on this object.