3N3

is unpredictable

Physics.
Teacher-in-charge: Mr chio
Students: Adlin, Diyanah, Elisa, Grace, Jermaine, Jingsheng, Pauline, Qianwei, Saiful, Tabatha, Vinis, Wende, Zongxian,

Speed, distance and time
The following is a basic but important formula which applies when speed is constant (in other words the speed doesn't change):Speed = distance/time

Remember, when using any formula, the units must all be consistent. For example speed could be measured in m/s, distance in metres and time in seconds.If speed does change, the average (mean) speed can be calculated:Average speed = total distance travelled/total time taken

Example:If a car travels at a speed of 10m/s for 3 minutes, how far will it travel?Firstly, change the 3 minutes into 180 seconds, so that the units are consistent. Now rearrange the first equation to get distance = speed × time.Therefore distance travelled = 10 × 180 = 1800m = 1.8km

Units
In calculations, units must be consistent, so if the units in the question are not all the same (e.g. m/s, m and s or km/h, km and h), change the units before starting, as above.

In line (1), we divide by 60 because there are 60 minutes in an hour. Often people have problems working out whether they need to divide or multiply by a certain number to change the units. If you think about it, in 1 minute, the object is going to travel less distance than in an hour. So we divide by 60, not multiply to get a smaller number.

Velocity and acceleration
Velocity is the speed of a particle and its direction of motion (therefore velocity is a vector quantity, whereas speed is a scalar quantity).When the velocity (speed) of a moving object is increasing we say that the object is accelerating. If the velocity decreases it is said to be decelerating. Acceleration is therefore the rate of change of velocity (change in velocity / time) and is measured in m/s².

Distance-time graphs
These have the distance from a certain point on the vertical axis and the time on the horizontal axis. The velocity can be calculated by finding the gradient of the graph. If the graph is curved, this can be done by drawing a chord and finding its gradient (this will give average velocity) or by finding the gradient of a tangent to the graph (this will give the velocity at the instant where the tangent is drawn).

Velocity-time graphs/speed-time graphs
A velocity-time graph has the velocity or speed of an object on the vertical axis and time on the horizontal axis. The distance travelled can be calculated by finding the area under a velocity-time graph. If the graph is curved, there are a number of ways of estimating the area (see trapezium rule below). Acceleration is the gradient of a velocity-time graph and on curves can be calculated using chords or tangents, as above.

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