Motion and Time – Time and Speed
* An object that covers less distance in a given time is said to be moving slow.
* The one that covers more distance in the same time is said to be moving fast.
* Speed is the distance covered by an object in unit time.
* An object moving along a straight line with a variation in speed is said to be in non – uniform motion.
* An object that maintains the same speed throughout the distance covered along a straight line is said to be in uniform motion.
* The speed of an object is calculated using the formula:
Speed = \frac{Distance \thinspace \thinspace covered}{Time \thinspace \thinspace taken}
* In ancient times, sundials, water clocks and sand clocks were used to measure time.
* All mechanical clocks use some kind of periodic/ oscillatory motion to show time.
* The time taken for one full oscillation is called the time period of the pendulum.
* A speedometer is a device used in vehicles to show the speed when the vehicle is in motion.
* An odometer is a device that is fixed in vehicles to show the distance covered by the vehicle.
* The unit of speed is metre per second, but generally, large speeds are measured in kilometre per hour.
International System of Units
* A unit is an internationally accepted basic reference standard against which the measurements of any physical quantity are compared.
* The units of fundamental or base quantities are called base units or fundamental units.
* The units of derived quantities, expressed as a combination of base units, are called derived units.
* The system of units is a generally accepted set of units of measurement which comprises base and derived units.