group 9 time rate and speed

Measuring Time



Time is the duration of an event.the SI unit of time is secongs(s),milliseconds(ms),minute(min) and hours(h).
The everyday instruments we use to measure time are watches and clocks.To measure a short period of time accurately, we use a stopwatch.there are two types: the mechanical and the electronic one.

The mechanical stopwatch has a minute scale and a second scale. The smaest divisi on the mechanical stopwatch is0.1ecs.Hence it is accurate to 01s.


how to use a mechanical stopwatch:
1.Press the operating button to start the stopwatch.
  Press the opearating button again to stop the timing.

2.press this button to reset the stopwatch.


ELECTRONIC STOPWATCH

The electronic stopwatch is more accurate then the mechanical stopwatch.It can measure time intervals accurate to 0.01 s.

It is better than the mechanical stopwatch as the readings are easily read off the digital display.

how to use a electronic stopwatch:
1. Press the "start/stop" button to start the stopwatch. Press the button again to stop the timing.
2.Press the "lap/split" button to reset the stopwatch.

WHAT IS RATE?

When we use the word rate, we usually mean how one quantity changes with time.Rates are useful  for making fair comparisons.

SPEED

the avg. sd =total distance travelled /total time taken
 When we say someone is moving too fast or too slow, we are making a statement about that person's speed.Speed is a rate of how fast or slow an object or person is moving.We use average speed to simplify calculations.the SI unit fof length is the metre,while the S.I unit of speed is metre per second(m/s).Other common units of speed are centimetre per seconds and kilometre per hour(km/h).

credits to :
stephanie,Wendy Gao and ashley yip and hui jin