IB Physics Sub-topic A1 Notes

Properties of motion

In Topic A.1, you need to focus on kinematics - the movement of objects, or motion. This is a fundamental concept in physics, and can be described with several terms:

1. distance (d) – the amount of space travelled, measured in m.
2. displacement (s) – the net distance an object has travelled from its starting point in a direction, measured in m.

1. speed (v or u) – the distance travelled per unit time, measured in m s^-1. v refers to the final speed and u to the initial speed.
2. velocity (v or u) – the displacement per unit time, measured in m s^-1. v refers to the final velocity and u to the initial velocity.
3. acceleration (a) – the velocity travelled per unit time or displacement travelled per square unit time, measured in m s^-2.

The matching equations are:

1. $\textrm{velocity (v)} = \frac{\textrm{displacement(s)}}{\textrm{time(t)}}$
2. $\textrm{speed (v)} = \frac{\textrm{distance(s)}}{\textrm{time(t)}}$
3. $\textrm{acceleration (a)} = \frac{\text{velocity (t)}}{\text{time (t)}} = \frac{\text{displacement (s)}}{\text{time (t)}^{2}}$

Remember that displacement, velocity, and acceleration are vectors, whereas speed is a scalar and is directionless.

An object’s measured velocity is also dependent on how it is measured and what it is measured in reference to. In motion experiments, velocity or acceleration are measured via:

1. light gates – a gate emits a beam of light and can calculate the average speed of the object based on how long it breaks the beam or how long it takes to travel between two gates.
2. strobe photography – light flashes at a set rate in front of a camera, capturing the object’s motion in pictures.