A useful diagram turns words into a picture with labels, values and directions. Drawing it first tells you which quantities are given, which are missing and which formula to use.
This page is for students who read a long problem and freeze. It is one of the help pages for SPM Physics.
What does this sound like?
A student might say, “I read the question three times and still do not know what to do.” Or, “I start writing formulas as soon as I see numbers.”
A problem in words hides the structure that a picture shows. The sketch is where the structure appears.
What usually causes it?
Three academic causes are common.
- The question is read once for the story and not scanned for values and directions.
- A force diagram is drawn from memory of a textbook picture, not from the forces in this problem.
- The diagram is drawn and then forgotten, so the calculation does not use it.
A worked example
A 12 kg crate is pushed along a floor by a horizontal force of 50 N. Friction of 20 N acts against the motion. Find the acceleration.
- Object: draw a box for the crate and write its mass, 12 kg.
- Forces: draw a 50 N arrow to the right, marked “push”, and a 20 N arrow to the left, marked “friction”. Add weight down and the normal reaction up, and note that they balance.
- Direction: take the direction of motion, to the right, as positive.
- Read off the physics: the net force is 50 − 20 = 30 N to the right, so a = F ÷ m = 30 ÷ 12 = 2.5 m s⁻².
The picture made the net force easy to see, and it showed that weight and normal reaction could be left out of the calculation.
What can you do on your own?
Use the same four steps every time.
| Step | What to do | What it prevents |
|---|---|---|
| Object | Draw and label it | Forgetting the mass |
| Forces | Draw each arrow with a name and value | Missing a force |
| Direction | Choose and mark the positive direction | Sign errors |
| Read off | Use the diagram for the formula | Choosing a formula by guesswork |
Underline the task in the question before drawing, as in finding the task in a question. The chapter lesson on drawing force diagrams covers the conventions, and I know the Physics formula but cannot choose one continues from the diagram to the equation.
When might one-to-one tuition help?
Drawing is a skill that improves by doing it, and you can check your sketch against the question’s words. If your diagrams often miss a force or confuse directions, it may help to have someone compare your sketch with the problem.
A one-to-one teacher can look at your diagram and ask what each arrow acts on. This catches errors like a force drawn on the wrong object. See online one-to-one Physics tuition or the one-hour trial class (from RM50).
What to read next
From the diagram, go on to choosing the equation in I know the Physics formula but cannot choose one.