This is a continuity note of Chapter 2 Force and Motion (Part 1) for Physics Form 4 syllabus. As mentioned in the previous note SPM Form 4 and 5 students need to have a good grasp of this chapter in Physics. Berry Berry Easy would like to present you Linear Motion which is provided by our new contributor, See Chee Keong. This subtopic is about the Distance and Displacemment in Form 4 SPM Physics syllabus. Most of the Pure Science Form 4 students would be curious to find out more about the distance and displacement of an object. Berry Berry Easy contributor will provide the further explanation on this matter.
SPM Physics Form 4 Notes – Force and Motion (Part 2)
Distance and displacement
Distance – the total length travels by the object. (Scalar quantity)
Displacement – the shortest distance between object and origin. (Vector quantity)
Figure 2.1 shows a circle with radius 7m, from the formula; we know that the circumference is 44m. A and B located at the same point. If an object move along the circumference from A to B,
- the distance in this travel is 44m
- the displacement in this travel 0m.
Since the A and B locate at same point, the shortest distance between object and origin is zero.
If a person move from point A to B then to C,
- the distance in this travel is 7m
- the displacement in this travel 5m.
Since the displacement is the shortest distance between object and origin that we can calculate the shortest distance which is CA by using Pythagorean theorem.
If a person moves from A to B then back to A and go to C. The total distance travel by the person is 5m, but the displacement is -1m. Since A is set as the origin, when the person moves from A to B, which can be said as the person moves in positive direction. When the person turns back from B to C, it is in the negative direction. Hence, students have to add the minus sign.
Displacement = 2m + (-2m) + (-1m) = -1m
“Please take note that not 2m – 2m – 1m but it should be 2m + (-2m) + (-1m), the reason for me to use + (- 2m) is that, in my view, there is no minus in dynamics; instead I will sum up everything. If it is in negative direction I will add a minus sign in front of the numeric value to indicate its direction.” – See Chee Keong