Motion and Time - Class 7 Science

Motion and Time

Important Points

Motion is always relative to a stationary point

To measure slow and fast motion, time is needed

SI unit of time is s(second)

Speed is the distance travelled by a body in a unit time.
SI unit of speed is m/s
Speed = Distance covered / Time taken

A uniform motion is when a body covers equal distance in equal intervals of time

A non-uniform motion is when a body covers unequal distances in equal intervals of time

Speed can be calculated from a distance-time graph by calculating its slope

The time period of a simple pendulum is the time taken to complete one oscillation
The time period of a simple pendulum does not depend upon the mass of the body

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Simple Pendulum

A simple pendulum contains a small mass(called bob), suspended from a fixed point through a long string or rod
The bob moves freely under gravity
The motion of pendulum is called oscillatory motion
When the bob of pendulum moves from one point, goes on the opposite side and comes back to its original position, it is said to complete one oscillation
The time taken by the pendulum to complete one oscillation is called its time period
The time period is independent of the mass of the bob
The time period of a pendulum depends upon the length of the string from which the bob is suspended. Longer the string, greater is the time period

Units of Time

60 seconds(s) = 1 minute(min)
60 min = 1 hour(hr)
24 hrs = 1 day
30 days = 1 month
365 days = 1 year
12 months = 1 year
10 years = 1 decade
100 years = 1 century
1000 years = 1 millineum

Practice Time

1. Fill in the blanks.
1. The speed of a body is distace covered in unit time.
2. To compare slow and fast motions, time needs to be measured.
3. Speed can be calculated from slope of a distance-time graph.
4. The SI unit of speed is m/s.
5. When a body covers equal distance in equal intervals of time, its motion is called uniform motion.
2. True or False.
1. A sand clock gives most accurate time
2. Motion of Earth around the sun is a non-uniform motion
3. Motion of a pendulum is a periodic motion
4. In a graph, the independent variable is plotted on X-axis
5. The time period of a simple pendulum changes with the length of the string
3. Choose the correct answers.
1. In a distance-time graph, distance is plotted on the
2. Among two moving objects, the object with higher speed will cover
3. The SI unit of speed is
4. A car moving on a highway with different speeds at different time. Its motion will be
5. A boy sitting in a moving car is in motion with respect to
4. Answer the following in one sentence
1. Name the axes of a graph
2. Give two examples of uniform motion
3. Give two examples of non-uniform motion
4. Which type of motion is shown by a pendulum?
5. Mention two ways in which the speed of an object can be increased.
5. Answer the following in brief
1. A toy train covers 240m distance in 2 minutes. Calculate its speed in m/s
2. A car was moving at a speed of 50km/hr. Calculate the distance covered by the car in 15 minutes.
6. Define the following in one sentence
1. Speed
2. Uniform motion
3. Time period of a pendulum
4. Slope of a graph
7. Define the following in detail
1. With the help of an example, explain how will you calculate the speed from a distance-time graph?
2. Explain the difference between uniform and non-uniform motion with examples
3. Discuss how man started measuring time
8. HOTS
1. Draw the distance time graph of a ball thrown upwards
2. Draw a rough distance-time graph of a ball thrown upwards
3. What type of motion is shown in the following graph? Explain your answer