0.2 Tg physical science - chapter contexts  (Page 6/10)

Motion in one dimension

This section explains how things move in a straight line or scientifically move in one dimension. Three ideas describe exactly how an object moves.

They are:

1. Position or displacement which tells us exactly where the object is;
2. Speed or velocity which tells us exactly how fast the object's position is changing or more familiarly, how fast the object is moving; and
3. Acceleration, which tells us exactly how fast the object's velocity is changing.

When studying motion, you need to know where you are, your position relative to a known reference point. The concept frame of reference, defined as a reference point combined with a set of directions (east, west, up down), is explained with illustrated examples. The illustrations on position are linked with learners’ everyday experience, making it easy for them to describe position and to understand that position can be positive or negative, relative to a reference point. The displacement of an object is defined as its change in position, a vector quantity, mathematically described as ∆x. In Mathematics and Science the symbol ∆ (delta) indicates a change in a certain quantity. For example, if the initial position of a car is $x_i$ and it moves to a final position of $x_f$ , then the displacement is $x_f–x_i$ . Displacement is written as:

$∆x=x_f-x_i$

Each of the concepts: speed, average velocity, instantaneous velocity and acceleration that describe motion are developed in words; definitions are stated, and suitable examples are discussed using illustrations. Equations are also used to interpret motion and to solve problems. Graphs, another way of describing motion, is also introduced in this section. The three graphs of motion: position vs. time, velocity vs. time and acceleration vs. time are discussed and presented simultaneously, starting with a stationary object. Learners will benefit by the way in which the content is developed, showing that graphs are just another way of representing the same motions previously described in words and diagrams. The text guides learners to extract information about movement from graphs by calculating the gradient of a straight line and the area under a graph.

The multiple examples discussed will clarify concepts developed, and by doing the exercises learners can assess their understanding. This section ends with the equations of motion, another way to describe motion. The curriculum prescribes that learners must be able to solve problems set on motion at constant acceleration. The text familiarise learners with these equations, and provides ample examples and exercises of problems to solve, set on real life experiences.

Mechanical energy

This section revises the concepts weight and mass, and explores the difference between mass and weight as an introduction to the energy concepts.

Gravitational potential energy is defined as the energy of an object due to its position above the surface of the Earth. In equation form gravitational potential energy is defined as:

$E_P=\mathrm{mgh}$

m = mass (measured in kg), g = gravitational acceleration (9; $\mathrm{8m}·s^{-2}$ ) and h = perpendicular height from the reference point (measured in m).