Let's talk forces
Physics Narrative for 5-11 11-14
Pushing and pulling
I was sitting in a train by the seaside quite recently. We had come to a halt and a steam engine went by pushing a line of four or so carriages. A small child sitting nearby called out excitedly:
Engine push wagons, push, push wagons!
The child's mother responded:
Yes, that's right, the big engine is pushing the wagons.
Ideas of pushing and pulling are common in everyday talk and are used from an early age as this example demonstrates. The word
force is used in a whole range of different ways: people refer to
force of habit or
forcing things open or
armed forces. In a tight corner you might argue:
you can't force me to do that!
In the sciences the concept of force is used in a more limited way and the good news is that the scientific way of thinking about forces is pretty close to everyday understanding. For example, when young children say:
I am lifting the bag or
we are pushing the trolley, they are starting to use the language of forces in ways which any scientist would recognise.
From such starting points, pupils need help in developing and applying a scientific description. In one sense this is not difficult: we are not expecting essays. A good starting point is to recognise that in describing situations where forces are acting, it is helpful to focus on three facets:
- What is the force exerted by?
- What kind of force is acting?
- What is the force acting on?
Let's apply these three questions to the example: "The engine pushes the wagons."
- The force is exerted by the engine.
- The force is a push.
- The force acts on the wagons.
This simple statement might be expressed slightly differently:
The push exerted by the engine acts on the wagons.
acts on is a good way of linking the force to whatever it is that feels the action of that force. Alternatively you might choose to link to what is providing the force. We suggest the consistent use of the word
exerts, in which case:
The engine exerts a push on the wagons.
Let's look at a second example:
The woman pulls on the rope.
- What exerts the force? The woman.
- What kind of force is acting? A pull.
- What is the force acting on? The rope.
You can develop your understanding of the kinds of forces through these next three resources.
But for now expect to find a force wherever something affects an object and you might have the same effect by pushing or pulling. Your push or pull can be identical to the action of the inanimate surroundings (the environment of the object) exerting a force on an object.