Measurement of Time and Motion - Class 7 Science Free MCQ Test with solutions

• The primary function of a speedometer is to display the current speed of the vehicle.
• It provides real-time feedback to the driver, helping them maintain safe speeds.
• Speedometers typically measure speed in miles per hour (mph) or kilometers per hour (km/h).
• This information is crucial for adhering to speed limits and ensuring safe driving conditions.

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.

Explanation:

Measuring time with high precision is very important in activities where even a fraction of a second can make a huge difference. For example, in athletics, swimming, or car racing, the winner is often decided by milliseconds.

• Cooking: Usually does not need extremely high precision; approximate minutes are enough.
• Watching movies: Time is measured, but precision is not critical.
• Gardening: No need for very precise timing.
• Sports timing in races: Requires highly precise measurement of time, often using electronic sensors and photo-finish cameras.

Hence, sports timing in races is a real-life application of measuring time with high precision.

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.

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 measure time using the regular vibrations of atoms or quartz crystals, which produce a steady oscillation that can be counted to mark uniform time intervals.

Atomic clocks use extremely stable atomic transitions (for example, the hyperfine transition of cesium) and give the highest precision, while quartz clocks use the mechanical vibrations of a crystal and are very accurate for everyday purposes.

Ancient methods-such as sundials that used shadows, water clocks that measured the flow of water, and timekeeping by natural cycles like day-night or seasons-relied on environmental or slowly varying phenomena and so were much less precise.

Because atomic and quartz vibrations are highly regular, modern clocks provide far greater precision and stability than ancient methods.

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 time period of a pendulum (time for one complete swing) depends mainly on the length of the string and the acceleration due to gravity.

• The mass of the pendulum does not affect the time period.

• The force of gravity is constant on Earth and affects the pendulum’s motion, but for practical purposes, the length of the string is the primary factor that can be controlled to measure time accurately.

The main factor that allows a pendulum to measure time is the length of the string.

Correct answer: (B) Length of the string