Motion And Time

CloseIn the SI system, the standard unit for measuring speed is metre per second, written as m/s. Here, metre is the unit of distance and second is the unit of time. Speed tells us how much distance is covered in one second, so metre per second is the most fundamental unit.

CloseFirst convert time into second. 2 minute = 2 × 60 = 120 second. Then speed = distance/time = 240 metre / 120 second = 2 metre per second. Always check that units are consistent before dividing.

CloseA renewable resource is one that can be used repeatedly and is naturally replenished on a human timescale, like energy from the sun. Coal, natural gas, and oil take millions of years to form and are non-renewable.

CloseIn a simple pendulum, a small heavy object called the bob is tied to a light string or thread. The other end of the string is fixed at a support. When the bob is pulled and released, it swings back and forth.

CloseWhen the bob moves from its mean position to one extreme, then to the other extreme, and back to the mean position, it completes one oscillation. This is also called one full swing.

CloseThe time period is the time required for one complete oscillation. For example, if a pendulum takes 2 second to swing back and forth once, its time period is 2 second. Its symbol is T, and unit is second.

CloseTime period = total time / number of oscillations = 40 second / 20 = 2 second. This means each oscillation takes 2 second.

CloseOscillatory motion is a back-and-forth or to-and-fro motion repeated regularly about a mean position. The pendulum bob moves left and right repeatedly, so it is oscillatory motion.

CloseMetre is a unit of length or distance, not time. Second, hour, and minute are all units used to measure time. The SI unit of time is second.

CloseSpeed tells us how fast an object moves. It is the distance covered per unit time. Mathematically, speed = distance / time. If an object covers more distance in the same time, it has higher speed.

CloseIn the SI system, each unit has a standard symbol. The symbol for second is s (always written in lowercase and singular). It is not written as sec or any other form.

CloseThe SI symbol for metre is m. It is written in lowercase and singular. For example, 5 metre is written as 5 m, not 5 ms or 5 M.

CloseKilometre is written with a small k and small m: km. Here k stands for kilo (meaning thousand) and m stands for metre. So 1 km = 1000 m.

CloseA stopwatch can measure time intervals up to a fraction of a second, such as 0.1 second or 0.01 second. It is used in experiments like finding the time period of a pendulum.

CloseSpeed = distance/time = 360 km / 6 h = 60 km/h. This means the bus covers 60 kilometre in one hour. The symbol km/h is read as kilometre per hour.

CloseFor a small bob, the time period depends mainly on the length of the pendulum. Longer the string, greater the time period. It does not depend on the mass of the bob.

CloseA longer pendulum takes more time to complete one oscillation because the bob has to travel a longer path. So time period increases with increase in length.

CloseFrequency is the number of oscillations per second. It is the reciprocal of time period. If time period is 0.5 second, frequency is 2 oscillations per second. Unit of frequency is hertz (Hz).

CloseA swing moves back and forth about a fixed position, just like a pendulum. That is oscillatory motion. A rotating fan has circular motion; a moving train has linear motion; a falling stone has rectilinear motion.

CloseTo convert m/s to km/h, multiply by 18/5. So 15 × (18/5) = 15 × 3.6 = 54 km/h. This is because 1 m/s = 3.6 km/h.

CloseA pendulum clock uses a swinging pendulum whose time period is constant for a fixed length. The movement of the pendulum is linked to gears that move the clock hands.

CloseUniform motion means the object covers equal distances in equal intervals of time. For example, a car moving at 20 metre per second without changing speed has uniform motion.

CloseAn odometer is a device in vehicles that shows the total distance travelled by the vehicle, usually in kilometre. It does not measure speed or time directly.

CloseTime period = total time / number of oscillations = 32 second / 16 = 2 second. Each oscillation takes exactly 2 second.

CloseSecond is the smallest unit among hour, minute, second, and day. 1 minute = 60 second, 1 hour = 3600 second, 1 day = 86400 second. The SI base unit of time is the second.

CloseWhen a ball bounces on the ground, it moves up and down repeatedly. This up-and-down motion about a mean position is oscillatory motion, though each bounce gets smaller.

CloseNon-uniform motion means the speed is changing. For example, a car starting from rest covers 5 metre in first second, 15 metre in next second, and so on. The distance covered in each second is different.

Close1 hour = 60 minute and 1 minute = 60 second. So 1 hour = 60 × 60 = 3600 second. This is useful when converting speed from km/h to m/s.

CloseThe upper end of the pendulum string is tied to a rigid support. This point remains fixed while the bob swings below it. It is also called the point of suspension.

CloseSpeed = distance / time = 600 metre / 30 second = 20 metre per second. This means the train covers 20 metre every second.

CloseTime period is a measure of time. Therefore its unit is second (s). It tells how many seconds one oscillation takes. It is not measured in metre (distance) or hertz (frequency).

CloseA pendulum wall clock has a visible swinging pendulum. The regular to-and-fro motion of the pendulum is used to control the movement of gears and thus measure time.

CloseAverage speed = total distance / total time = 90 km / 1.5 h = 60 km/h. Dividing 90 by 1.5 is same as 90 ÷ (3/2) = 90 × (2/3) = 60.

CloseWhen the pendulum bob is hanging straight down and not moving, it is at its mean position. From here, it swings to the left extreme, back to mean, to the right extreme, and back to mean.

CloseTime period is defined as the time for one oscillation. So if one oscillation takes 5 second, the time period is exactly 5 second. No calculation is needed.

CloseKilometre per hour (km/h) is a compound unit that measures how many kilometre are covered in one hour. That is exactly the definition of speed.

CloseThe time period of a pendulum also depends on gravity. On the Moon, gravity is weaker (about 1/6th of Earth’s gravity). A weaker gravity makes the pendulum swing more slowly, so time period increases.

CloseA sea-saw moves up and down repeatedly. One end goes up while the other goes down, and then they reverse. This back-and-forth motion is oscillatory.

CloseTo convert km/h to m/s, multiply by 5/18. So 72 × (5/18) = 72 × 5 ÷ 18 = 360 ÷ 18 = 20 m/s. Remember: multiply by 5/18 to go from km/h to m/s.

CloseSpeed is distance divided by time, so its unit is a unit of distance divided by a unit of time, like m/s, km/h, cm/s. s/m would be time per distance, which is not speed.

CloseThis is the definition of time period. Frequency is number of oscillations per second. Amplitude is the maximum displacement from mean position.

CloseSpeed = distance/time = 500 metre / 250 second = 2 metre per second. He walks 2 metre every second.

CloseWhen you pull the bob to one side, the distance from the mean position to that extreme point is the amplitude. Larger amplitude means the bob swings wider.

ClosePeriodic motion is any motion that repeats at regular intervals of time. Oscillatory motion is a type of periodic motion. The swinging of a pendulum is periodic.

CloseDistance = speed × time = 30 m/s × 10 s = 300 metre. If it moves at 30 metre per second, in 10 seconds it covers 300 metre.

CloseThe standard symbol for hour is h. It is written in lowercase and singular. For example, 3 hour is written as 3 h, not 3 hrs.

CloseUniform motion means constant speed in a straight line. A fan blade moves in a circle but at constant speed, so its speed is uniform. The other options involve changing speed.

CloseNumber of oscillations = total time / time period = 30 second / 1.5 second = 20. So in 30 second, it swings back and forth 20 times.

CloseThe SI symbol for metre per second is m/s. It is written with a forward slash. Do not write mps or m.s. The symbols m and s are both singular.

CloseMeasuring time for many oscillations reduces the error caused by human reaction time. For example, if you measure time for 20 oscillations, any small mistake gets divided by 20, giving a more accurate time period.