Test: Measurement of Time and Motion - Class 7 MCQ

"Ghatika" is an old unit of time used in India, equal to 24 minutes. It was used in ancient timekeeping devices like water clocks.

Atomic clocks are modern devices that measure time very accurately using atoms, unlike older methods like water clocks, hourglasses, and candle clocks.

Uniform linear motion happens when an object moves at a constant speed along a straight path.

A speedometer shows the speed at which the vehicle is moving.

Non-uniform motion occurs when the speed changes, like when a bike accelerates downhill.

A sundial measures time by using the shadow of a stick (gnomon) that changes position as the Sun moves across the sky.

Sports events, especially races, use very precise timers to measure times down to fractions of a second.

Uniform motion happens at a constant speed, while non-uniform motion involves changes in speed.

Average speed is calculated by dividing the total distance by the total time taken.

Ancient people measured time by observing natural events, like the rising and setting of the Sun or the phases of the Moon.

Speed, distance, and time are related by the formula: Distance = Speed × Time. This helps in calculating any one of these if you know the other two.

A water clock measures time by allowing water to flow into or out of a container at a steady rate.

The time period of a simple pendulum is not affected by the mass of the bob but depends on the length of the string and gravity.

Speed is defined as the distance traveled divided by the time it takes to cover that distance.

An odometer measures the total distance traveled by a vehicle.

The time period of a simple pendulum depends on the length of its string. A longer string makes the pendulum take more time to complete a swing.

Modern clocks, like atomic and quartz clocks, measure time very precisely using the vibrations of atoms or quartz crystals.

Speed is measured as distance per time, like meters per second (m/s) or kilometers per hour (km/h), not mass per time.

The SI (International System) unit for time is the second, represented as "s."

The correct answer is:

b) The force of gravity

Explanation:

A pendulum measures time because of the principle of isochronism — its time period depends mainly on the length of the string and the force of gravity, not on the mass of the bob.

• Force of gravity provides the restoring force that makes the pendulum swing back and forth.
• Length of the string affects the time period (longer string = slower swing, shorter string = faster swing).
• Mass of the pendulum does not affect the time period.

So the key principle that allows a pendulum to measure time is the force of gravity.